A plain-language glossary of file formats — what each one is and how to use an example of it for testing. Every entry links to real, downloadable example files in the library.
File format
3DS is the chunked binary scene format associated with the original 3D Studio. Every structure begins with a 16-bit chunk identifier and a 32-bit length, allowing readers to skip unknown chunks while extracting meshes, faces, texture coordinates, materials, cameras, and keyframe data within its historical naming and index limits.
File format
3GP is the mobile profile of the ISO base media file format, defined by 3GPP for 3G handsets and for video sent over MMS. It shares MP4's box structure and announces itself with an `ftyp` brand such as `3gp4` or `3gp6`, but wraps H.263, MPEG-4 Part 2, or H.264 video with AMR-NB, AMR-WB, or AAC audio at bitrates a 2000s cellular link could sustain. Almost every .3gp file in the wild is an old camera-phone capture; the near-identical .3g2 is 3GPP2's version for CDMA2000 networks.
File format
3MF (3D Manufacturing Format) is a modern XML-based 3D printing format packaged as a ZIP archive, designed to fix STL's limitations by including color, materials, units, and multiple objects. It carries full model and print metadata in a single file. It is increasingly the preferred format for 3D-print workflows.
File format
7z is the native archive format of 7-Zip, supporting high-ratio LZMA and LZMA2 compression, strong AES-256 encryption, and solid compression across multiple files. It bundles many files with a flexible header and typically outperforms ZIP on compression. It is popular for efficient archiving and distribution.
File format
AAC (Advanced Audio Coding) is a lossy audio format that generally outperforms MP3 at the same bitrate, standardized as part of MPEG-2 and MPEG-4. Raw AAC streams use ADTS framing, while AAC is also commonly wrapped in M4A or MP4 containers. It is the default audio codec for Apple, YouTube, and streaming.
File format
AC-3 (Dolby Digital) is a lossy multichannel audio codec designed for surround sound, supporting up to 5.1 channels. It is standard for DVDs, digital broadcast, and home-theater audio tracks. Raw AC-3 files carry the encoded surround bitstream directly.
File format
AsciiDoc is a lightweight plain-text markup language for writing documentation, articles, and books. It is more powerful than Markdown — with admonitions, includes, tables, and cross-references — and converts to HTML, PDF, DocBook, and man pages via tools like Asciidoctor. The .adoc extension is the common file type.
File format
AIFF (Audio Interchange File Format) is an Apple-originated container storing uncompressed big-endian linear PCM audio. It is functionally analogous to WAV but uses a different chunk layout and byte order, offering lossless high-fidelity sound. It is common in professional audio on macOS.
File format
AMF (Additive Manufacturing File Format) is an XML format for 3D-printing geometry and manufacturing metadata. It represents objects as vertices and triangular volumes and can also describe units, materials, colours, textures, constellations, and metadata without the ambiguity of a unitless STL file.
File format
AMR (Adaptive Multi-Rate) is a lossy speech codec optimized for narrowband human voice at very low bitrates, widely used in GSM and UMTS mobile telephony. It is efficient for spoken audio but poor for music. It commonly appears in voice recordings and MMS messages.
File format
APNG (Animated PNG) extends the PNG format with animation by adding frame-control chunks while remaining backward compatible with static PNG decoders. It supports full 24-bit color and 8-bit alpha per frame, unlike GIF's 256-color limit. It is used for high-quality short animations.
File format
The Unix ar archive (.ar/.a) is a simple concatenation format with a magic header and 60-byte member headers, used mainly for static libraries (libfoo.a) and Debian .deb packages. It stores files without compression.
File format
An ARB file (.arb, Application Resource Bundle) is a JSON-based localization format used by Flutter and Google tools. Alongside each key's translated string it stores metadata in a matching @key object — a description and typed placeholders — and uses ICU message syntax with {name} placeholders and plural/select rules.
File format
ASS (Advanced SubStation Alpha, .ass) is a feature-rich subtitle format that extends SSA with precise styling, positioning, fonts, colours, and animation override tags. It is the standard for fansubs and anime, and is rendered by libass in players like VLC and mpv.
File format
Atom is an XML-based web syndication format standardized by the IETF as a more rigorous alternative to RSS. It publishes entries with structured metadata including unique IDs, updated timestamps, and typed content. It is used for blogs, news, and API feeds.
File format
AU (Sun/NeXT audio) is a simple audio format with a short header followed by sample data, historically using 8-bit mu-law or linear PCM encoding. It is a legacy Unix-world format that is compact and easy to parse. It appears in older systems and Java audio contexts.
File format
AVI (Audio Video Interleave) is a legacy Microsoft multimedia container built on the RIFF structure that interleaves video and audio streams. It predates modern features, lacking robust support for advanced codecs, streaming, and multiple subtitle tracks. It remains common in older video files.
File format
AVIF is a raster image format that stores AV1-encoded still images inside an ISOBMFF container. It offers high compression efficiency with support for wide color gamut, HDR, alpha transparency, and animation. It is supported by most current browsers and delivers small files at high quality.
File format
Apache Avro (.avro) is a compact binary, row-oriented data format that stores its JSON schema in the file header alongside the records, enabling schema evolution. It is widely used with Kafka and Hadoop for message and data serialization.
File format
AZW is an early Amazon Kindle e-book container derived from the Palm Database and Mobipocket family. Unencrypted files combine a PalmDB record table with text, metadata, and optional image records; commercial AZW books may carry DRM, which a test fixture should not include or imply it can remove.
File format
AZW3 (.azw3, Kindle Format 8) is Amazon's e-book format based on EPUB-like HTML/CSS wrapped in a Mobipocket/PDB container, supporting richer layout than the older MOBI. It is used by Kindle devices and apps.
File format
BDF (Glyph Bitmap Distribution Format) is a plain-text format for bitmap fonts from the X11 world. Each glyph is described by a small grid of pixels given as hex rows, along with metrics and encoding. It is human-readable and was the standard way to ship fixed-size screen fonts before scalable outlines.
File format
BED is a tab-delimited format for genomic intervals. The first three columns — chromosome, 0-based start, and exclusive end — are required, and up to nine optional columns add name, score, strand, thick-drawn range, colour, and block (exon) structure. The half-open, zero-based coordinate convention is the single most common source of off-by-one errors when converting to or from GFF3 and other 1-based formats.
File format
BibTeX (.bib) is a plain-text bibliography database used with LaTeX and reference managers. Each entry has a type (@article, @book, @inproceedings), a citation key, and tagged fields like author, title, year, and journal. It is the standard citation format in academic writing.
File format
A .bin file is a generic binary blob with no specific format — raw bytes whose meaning depends entirely on the producing application (firmware images, memory dumps, serialized payloads). The extension signals only 'not text.'
File format
BMP (Windows Bitmap) is an uncompressed or lightly RLE-compressed raster format that stores pixels in a simple device-independent layout. Files are large because pixel data is typically stored raw, often bottom-up, with various bit depths from 1 to 32 bits per pixel. It is a legacy Windows format still useful as a lossless intermediate.
File format
BSON (Binary JSON, .bson) is the binary-encoded serialization MongoDB uses to store documents. It extends JSON with typed values (ObjectId, dates, binary, decimal128) and length-prefixed fields for fast traversal.
File format
BZ2 is a file compressed with bzip2, which uses the Burrows-Wheeler transform to achieve higher compression ratios than gzip at the cost of slower speed. Like gzip, it compresses a single stream rather than archiving multiple files. It is common for distributing large source and data files.
File format
C (.c) is a plain-text source file for the C programming language — a low-level, statically typed, compiled language that maps closely to hardware. It underpins operating systems, embedded firmware, and language runtimes, using manual memory management, pointers, structs, and the preprocessor.
File format
CAB is Microsoft's Cabinet archive format for bundling compressed files and installation resources. An MSCF header points to folder and file tables; data blocks may use no compression, MSZIP, Quantum, or LZX, and a cabinet can participate in a multi-volume set.
File format
CBOR (Concise Binary Object Representation, .cbor, RFC 8949) is a compact, self-describing binary data format modelled on JSON but extended with binary strings, tags, and streaming. It is used in IoT, COSE/WebAuthn, and constrained protocols.
File format
CBR is a comic-book archive convention: a RAR container whose member images are interpreted as ordered pages. The extension adds no new container structure, so page order depends on safe archive extraction and natural filename sorting, while metadata may live in an optional ComicInfo.xml member.
File format
CBZ (Comic Book ZIP) is a ZIP archive holding a sequence of image files, typically named so they sort into page order, used to distribute comics and manga. It carries no compression benefit beyond ZIP and relies on filename ordering for pagination. Readers display the images as consecutive pages.
File format
CIF (Crystallographic Information File) is the IUCr's standard text format for crystal structures. It is a tagged plain-text format in which `_data_name value` pairs and `loop_` blocks carry unit-cell parameters, symmetry operations, atom sites with fractional coordinates and occupancies, and full experimental provenance. mmCIF, its macromolecular profile, is now the archival format of the Protein Data Bank.
File format
Clojure (.clj) source files contain Lisp-dialect programs for the JVM, emphasizing immutable data and macros.
File format
A .conf text file here is an OpenSSH-style client configuration SAMPLE with Host stanzas for fictional hosts.
File format
A .cpg file is a one-line sidecar naming the character encoding used by a shapefile's .dbf attribute table — typically UTF-8, or a legacy code page such as ISO-8859-1 or CP1252. The dBase format has no reliable in-band encoding declaration, so without this file a reader has to guess, and non-ASCII attribute values come back as mojibake.
File format
cpio (.cpio) is a classic Unix archive format that concatenates files with per-file headers, used by initramfs images and RPM payloads. The 'newc' (SVR4) variant is the modern portable form.
File format
C++ (.cpp) is a plain-text source file for the C++ programming language — a statically typed, compiled language that extends C with classes, templates, operator overloading, the Standard Template Library, and RAII. It is used for high-performance applications, game engines, and systems software.
File format
A .crt file holds an X.509 certificate, most often PEM-encoded (Base64 text) though sometimes DER binary. The extension is a convention for the public certificate half of a TLS identity, as opposed to the private .key file. It carries the subject, issuer, validity window, public key, and signature.
File format
C# (.cs) is a plain-text source file for Microsoft's C# language — a statically typed, object-oriented language on .NET. It features classes, records, LINQ, async/await, and nullable reference types.
File format
A CSR (Certificate Signing Request, PKCS#10) is a PEM-encoded request a party sends to a certificate authority to be issued a certificate. It contains the subject distinguished name and public key, self-signed with the matching private key to prove possession, but has no validity dates or issuer.
File format
CSS (.css) is a plain-text stylesheet describing how HTML elements are presented — colors, layout, typography, and responsive behaviour. It uses selectors paired with declaration blocks, and modern CSS adds custom properties (variables), flexbox and grid layout, and media queries.
File format
CSV (Comma-Separated Values) is a plain-text tabular format where rows are lines and fields are separated by commas, with quoting rules for values that contain delimiters, quotes, or newlines. It has no formal type system and depends on encoding and dialect conventions. It is the most portable format for tabular data exchange.
File format
A CUE sheet is a plain-text description of tracks and index points within one or more audio files. FILE, TRACK, TITLE, PERFORMER, INDEX, and optional pregap directives describe how a continuous recording should be divided; INDEX times use minute:second:frame notation with 75 frames per second rather than video timecode.
File format
A cursor file (.cur) is a Windows mouse-pointer image using the same container structure as an .ico, distinguished by a type field and per-image hotspot coordinates that mark the cursor's active point. It holds one or more bitmap images at different sizes, typically 32×32.
File format
CWL (Common Workflow Language) is an open standard for describing command-line analysis workflows portably. A .cwl document is YAML (or JSON) declaring a cwlVersion and a class of CommandLineTool, Workflow, or ExpressionTool, with typed inputs and outputs, input bindings that map values onto command-line arguments, and — for workflows — steps wired together by source references. Requirements and hints declare the container image and resources a step needs.
File format
COLLADA (.dae, Digital Asset Exchange) is an XML-based 3D interchange format for meshes, materials, scenes, and animation. It was a common exchange format between DCC tools and early WebGL/AR pipelines.
File format
Dart (.dart) is a plain-text source file for the Dart language used by Flutter and Dart VM apps. It is object-oriented with sound null safety, async futures/streams, and a concise syntax.
File format
A dBASE table (.dbf) is a legacy binary tabular format with a fixed-width header describing columns (name, type, length) followed by fixed-length records. It persists today as the attribute table of GIS shapefiles and in legacy database exchange.
File format
DER (Distinguished Encoding Rules) is the binary encoding of an X.509 certificate (or other ASN.1 structure) — the same data a PEM file Base64-wraps, without the text armour. A .der certificate is compact and byte-exact, common in Java keystores and Windows tooling.
File format
DFXP (Distribution Format Exchange Profile, .dfxp) is the original name for what became TTML, and the extension is still in wide use — notably by Netflix, Adobe, and older captioning tool-chains. The bytes are TTML: the same tt root element, the same head/body/div/p structure, the same timing and region attributes. The extension signals provenance, not a different grammar.
File format
A .diff file records the difference between two versions of one or more text files. The unified format — the default almost everywhere — names the old and new files on `---` and `+++` lines, then lists hunks introduced by `@@ -old,count +new,count @@` in which context lines are unprefixed and changed lines are prefixed with `-` or `+`. Older context and normal diff formats exist but are rarely produced today.
File format
A .doc file is the legacy binary Microsoft Word format (Word 97–2003) using the OLE2 compound-file structure, distinct from the modern XML-based .docx. It is still encountered in archives and legacy document flows.
File format
A Dockerfile is a plain-text script of instructions that Docker reads to build a container image layer by layer, using directives like FROM, RUN, COPY, and CMD. Each instruction defines a step in assembling a reproducible image. It is the standard definition format for containerized applications.
File format
DOCX is the default Microsoft Word format, an Office Open XML document packaged as a ZIP archive of XML parts, media, and relationships. It stores structured text, styles, tables, images, and metadata. It is the dominant format for editable word-processing documents.
File format
A DOT file is a Graphviz graph described in the DOT language — nodes, edges, and attributes as plain text — which Graphviz lays out and renders to an image. It is a standard way to define directed and undirected graphs as code.
File format
A DRAWIO file is a diagram in draw.io / diagrams.net's native format — an XML document (mxGraphModel) describing shapes, styles, geometry, and connections. It is the working format the draw.io editor saves and re-opens.
File format
DRC is a common extension for a Google Draco compressed geometry stream. Draco entropy-encodes mesh or point-cloud connectivity and attributes such as position, normal, colour, and texture coordinates; the file is a compact geometry payload rather than a complete scene with materials and external resources.
File format
DTS is a framed perceptual audio bitstream used for multichannel cinema, disc, and media delivery. A stream carries sync words, frame headers, sample-rate and channel-mode information, and compressed audio blocks; byte order and padded variants mean a parser must inspect the bitstream rather than rely on the suffix.
File format
DXF (Drawing Exchange Format) is an Autodesk CAD interchange format, typically ASCII, that represents 2D and 3D drawing entities like lines, arcs, layers, and text. It was created to move drawings between CAD programs and is broadly supported. It stores vector CAD geometry rather than a rendered image.
File format
EDI (Electronic Data Interchange), in the ANSI X12 family, is a structured plain-text format for exchanging business documents like purchase orders (850) and invoices (810) between trading partners. It is built from segments (ISA, GS, ST, …) separated by delimiters, with tightly specified element positions. It underpins much of B2B supply-chain and retail commerce.
File format
EDL usually means a CMX 3600 edit decision list: a line-oriented interchange format that records reel names, edit numbers, source and record timecodes, track selection, and simple transition codes. It represents the editorial decisions rather than embedding media, so reel identifiers and frame-rate interpretation are essential to relinking the referenced clips.
File format
An EML file is a single email message stored in the RFC 822 / MIME format — plain-text headers (From, To, Subject, Date, Message-ID) followed by the body, which may be plain text, HTML, or a multipart structure with alternative bodies and file attachments encoded in base64.
File format
ENV files (dotenv) are plain-text lists of KEY=VALUE pairs used to define environment variables for an application, one per line with optional comments. They are conventionally excluded from version control because they often hold configuration and secrets. Parsing rules for quoting and interpolation vary by library.
File format
EPS (Encapsulated PostScript) is a single-page PostScript program restricted enough that another document can place it as a picture. The spec requires a `%!PS-Adobe-3.0 EPSF-3.0` header and a `%%BoundingBox` comment giving the artwork's extent, and forbids operators that would disturb the host page. Windows files often begin instead with a 30-byte binary header (`C5 D0 D3 C6`) indexing an appended TIFF or WMF preview — the reason a placed EPS looks coarse on screen yet prints sharply. Adobe now steers new work to PDF and SVG.
File format
EPUB is the open e-book standard, a ZIP archive containing XHTML content documents, CSS, images, and a package manifest describing reading order and metadata. It supports reflowable text that adapts to screen size and is supported by most e-readers except Kindle natively. It is the dominant format for distributable e-books.
File format
Elixir (.ex) is a plain-text source file for the Elixir language on the Erlang VM. It emphasises functional programming, pattern matching, and fault-tolerant concurrency via actors (processes).
File format
Fortran 90 (.f90) source files contain modern free-form Fortran programs used in numerical and scientific computing.
File format
FASTA is the plain-text format for biological sequences. Each record begins with a `>` header line carrying an identifier and free-form description, followed by the sequence itself wrapped over as many lines as needed using IUPAC single-letter codes for nucleotides or amino acids. It records no quality or alignment information, which is what keeps it universal.
File format
FASTQ pairs each sequence with per-base quality scores. A record is exactly four lines: a `@` header, the sequence, a `+` separator that may repeat the header, and a quality line of the same length whose characters encode Phred scores as ASCII with an offset — 33 in the Sanger/Illumina 1.8+ encoding, 64 in older Illumina data. Misidentifying that offset silently shifts every quality value by 31.
File format
FB2 (FictionBook) is an XML-based e-book format that stores an entire book, including metadata and embedded images, in a single well-structured XML file. It emphasizes semantic markup of book structure over fixed presentation. It is especially popular in the Russian-speaking e-book community.
File format
FBX is Autodesk's scene-interchange format for meshes, transforms, materials, animation, cameras, lights, and hierarchy. It has both text and binary encodings; the binary form begins with a recognizable header and stores a versioned tree of typed records whose connections define relationships between scene objects.
File format
FCPXML is Apple's XML interchange format for Final Cut Pro libraries, events, projects, timelines, resources, effects, and metadata. Time values are commonly expressed as rational seconds, resources are declared once and referenced by identifier, and the document version controls which elements and attributes an importer may accept.
File format
FDF (Forms Data Format) is Adobe's format for carrying the field values of a PDF form separately from the document itself. An FDF file lists each form field name and its value and can reference the PDF it belongs to, so form data can be exchanged, imported, and exported without resending the whole PDF. It is the classic companion to interactive AcroForm PDFs.
File format
Feather (.feather) is a fast on-disk representation of Apache Arrow tables designed for zero-copy, language-agnostic data exchange between Python (pandas/pyarrow) and R. It preserves column types and structure exactly.
File format
A .feature file holds a Gherkin specification: a business-readable, plain-text description of behaviour written as Feature, Background, Scenario, and Scenario Outline blocks whose steps begin with Given, When, Then, And, or But. Scenario Outlines are parameterised by an Examples table, and tags such as @smoke mark subsets of the suite. Cucumber, Behave, SpecFlow, and Behat all read the same grammar, with localised keyword sets available for non-English specifications.
File format
FITS (.fits, Flexible Image Transport System) is the standard binary format in astronomy. It pairs human-readable 80-character header cards (in 2880-byte blocks) with binary image or table data, storing pixel arrays, coordinates, and instrument metadata. It has been the astronomical archive format for decades.
File format
FLAC (Free Lossless Audio Codec) compresses PCM audio losslessly, typically to about half the size of the original with no quality loss. It supports metadata tags, embedded cover art, and fast seeking. It is favored for archival and audiophile music libraries.
File format
FLV (.flv, Flash Video) is a legacy container that carried H.264/VP6 video and MP3/AAC audio for Adobe Flash Player and RTMP streaming. Flash is retired, but FLV files persist in archives and legacy pipelines.
File format
Fluent (.ftl) is Mozilla's localization file format for natural-sounding translations with placeholders, plurals, and selectors. Catalogs are plain text and designed for readable, maintainable UI strings.
File format
GeoJSON is a JSON-based format for encoding geographic data structures such as points, lines, and polygons, along with their properties. It uses WGS84 longitude-latitude coordinates and standard feature and feature-collection objects. It is a common interchange format for web mapping and GIS.
File format
GEXF (Graph Exchange XML Format) is an XML format for graphs created for the Gephi network-analysis tool. It describes nodes and edges with attributes and also supports dynamic (time-evolving) graphs and visual properties like position and colour. It is a common interchange format alongside GraphML.
File format
GFF3 (General Feature Format version 3) is a tab-delimited format for genome annotations. Each line has nine columns — seqid, source, type, 1-based inclusive start and end, score, strand, phase, and a semicolon-separated attributes column — and parent/child relationships between genes, transcripts, and exons are expressed through ID and Parent attributes. Directives beginning with `##` carry metadata such as the sequence region.
File format
GIF (Graphics Interchange Format) is a raster format limited to a 256-color indexed palette per frame, using lossless LZW compression. It supports simple frame-based animation and a single fully transparent palette index. It is widely used for short looping animations and low-color graphics.
File format
A .gitattributes file assigns per-path attributes that change how Git handles matching files. It controls end-of-line normalisation (`text`, `-text`, `eol=lf`), diff and merge drivers, export filtering, `linguist-*` language hints, and Git LFS filters, using the same pattern syntax as .gitignore with attributes listed after each pattern.
File format
A .gitconfig file holds Git configuration in an INI-like syntax: bracketed section headers, optional subsection names in quotes, and `key = value` pairs. The same grammar serves the system, global, and per-repository files, which are layered in that order, and values may be booleans, integers with `k`/`m`/`g` suffixes, colours, or paths. Comments begin with `#` or `;`.
File format
A .gitignore file tells Git which untracked paths to leave alone. Each line is a pattern: a leading `/` anchors it to the containing directory, a trailing `/` restricts it to directories, `!` re-includes a previously excluded path, `**` matches across directory boundaries, and `#` introduces a comment. Rules are evaluated in order, with the last matching pattern winning, and nested .gitignore files layer on top of parent ones.
File format
A .gitmodules file records the submodules of a Git repository. It uses the same INI-like grammar as .gitconfig, with one `[submodule "name"]` section per entry holding the working-tree `path`, the `url` to clone from, and optionally `branch`, `update`, `shallow`, and `ignore` settings. It is tracked in the repository, unlike the resolved submodule state, which lives in the index as gitlink entries.
File format
GLB is the binary form of glTF, packaging 3D scene geometry, materials, textures, animations, and node hierarchy into a single self-contained file. It is optimized for efficient runtime loading and is often called the JPEG of 3D. It is widely used in web, AR, and real-time 3D applications.
File format
glTF (.gltf, GL Transmission Format) is the 'JPEG of 3D' — a JSON scene description referencing geometry, PBR materials, textures, and animation, with binary buffers stored alongside or as a .bin. It is the standard for web and real-time 3D.
File format
GML (Geography Markup Language) is the OGC's XML grammar for geographic features. Features carry typed properties and geometry elements such as gml:Point, gml:LineString, gml:Polygon, and their aggregates, with coordinates in gml:posList or gml:coordinates and the coordinate reference system named by an srsName attribute. It is the payload format of WFS services and the base of several national and INSPIRE data standards.
File format
Go (.go) is a plain-text source file for the Go programming language — a statically typed, compiled language from Google designed for simplicity and concurrency. It features goroutines and channels, a fast compiler, garbage collection, structs with methods, and interfaces, with a strict standard formatting.
File format
GeoPackage is an OGC standard that stores vector features, raster tiles, and their metadata inside a single SQLite database. Required tables such as gpkg_contents, gpkg_spatial_ref_sys, and gpkg_geometry_columns describe what the file holds, and feature geometries are stored in a standard binary header followed by Well-Known Binary. Being one self-contained file with real SQL indexing, it is the modern replacement for the multi-file shapefile.
File format
GPX (GPS Exchange Format) is an XML schema for GPS data, storing waypoints, routes, and tracks with coordinates, elevation, and timestamps. It is the standard interchange format for GPS devices and fitness and navigation apps. Track points capture recorded movement over time.
File format
A .gradle file is a Gradle build script written in the Groovy DSL. It configures a project through blocks such as plugins, repositories, dependencies, and tasks, where each block is really a Groovy closure evaluated against a delegate object — which is why a build script is executable code rather than static configuration. The Kotlin DSL equivalent uses the .gradle.kts extension.
File format
GraphML is an XML-based format for describing graphs — nodes, edges, and typed attributes (keys) on either. It supports directed and undirected graphs, and is widely read by network tools such as Gephi, NetworkX, and yEd. Being plain XML, it is human-readable and easy to transform.
File format
GraphQL files contain schema definitions or operations written in the GraphQL Schema Definition Language, describing types, fields, queries, and mutations. The schema defines a strongly typed API contract that clients query for exactly the data they need. It is a common alternative to REST for API design.
File format
GZ is a file compressed with gzip, using the DEFLATE algorithm within a simple single-stream container that stores one compressed file plus a small header and checksum. It compresses a single stream rather than bundling multiple files. It is ubiquitous for compressing logs, tarballs, and HTTP responses.
File format
HDF5 (.h5) is a binary container format for large, heterogeneous scientific data. It stores multidimensional arrays (datasets) in a hierarchical group structure with attributes and chunked, compressed storage, and is standard in ML, physics, and geoscience.
File format
HAR (HTTP Archive) is a JSON format that records a browser or client's network activity. A log object carries the creator, one or more pages, and an ordered list of entries, each holding a full request and response — method, URL, headers, cookies, query string, POST data, status, content, transfer sizes — plus per-phase timings for DNS, connect, send, wait, and receive. Every major browser's developer tools can export one.
File format
HCL (HashiCorp Configuration Language) is the block-structured configuration language behind Terraform, Packer, Nomad, Consul, and Vault. A document is a sequence of attributes (`name = expression`) and blocks (a type, zero or more string labels, and a braced body), with support for heredocs, function calls, conditionals, and for-expressions. It is designed to be both hand-written and machine-generated, and has a documented JSON-equivalent syntax.
File format
A .headers text fixture is a plain-text dump of HTTP response headers (CORS, CSP, HSTS, etc.) used for policy and scanner tests.
File format
HEIC is the HEIF container variant holding HEVC (H.265)-encoded still images, the default photo format on modern Apple devices. It offers strong compression with support for high bit depth, wide color, and image sequences or bursts. Decoding requires HEVC support, which is patent-encumbered and not universal.
File format
HEIF (High Efficiency Image Format) is an ISOBMFF-based container for storing images and image sequences, most often with HEVC-encoded content. It supports high bit depth, transparency, thumbnails, and multi-image collections. HEIC is its most common concrete variant.
File format
HL7 v2 is the dominant messaging standard for exchanging clinical and administrative data between healthcare systems. A message is plain text made of segments (one per line, e.g. MSH, PID, PV1), each split into fields by pipe (|) delimiters, with components separated by carets (^). It drives admissions, lab orders, and results across hospitals.
File format
Haskell (.hs) source files contain programs in the pure functional Haskell language, typically compiled with GHC.
File format
HTML (HyperText Markup Language) is the structural markup language of the web, using nested tags to define document content, semantics, and links. It is typically paired with CSS for presentation and JavaScript for behavior. It is the foundational format rendered by browsers.
File format
An .htpasswd file stores usernames and hashed passwords for HTTP Basic Authentication, one user per line as user:hash. The hash is typically bcrypt, Apache MD5 (apr1), or SHA — never plaintext. Apache and nginx read it to guard a directory or route.
File format
ICO is a Windows icon container that bundles multiple image sizes and bit depths in a single file so the system can pick the best resolution. Each entry is stored as a BMP-style bitmap or embedded PNG, commonly at sizes like 16, 32, and 48 pixels. It is the traditional format for application and website favicons.
File format
ICS (iCalendar) is a plain-text format for exchanging calendar data such as events, to-dos, and free/busy time, structured as nested VCALENDAR and VEVENT components with property lines. It encodes start and end times, recurrence rules, and reminders. It is the universal standard for calendar interchange and invitations.
File format
IGES (Initial Graphics Exchange Specification) is an older neutral CAD format for exchanging 2D and 3D geometry such as curves, surfaces, and wireframes as structured text records. It predates STEP and remains supported for legacy interoperability. It stores precise geometry rather than tessellated meshes.
File format
INI is an informal configuration format organizing key-value pairs under bracketed section headers, with comment lines and no strict standard. Parsing details like comment characters, quoting, and nesting vary between implementations. It is a long-standing choice for simple application and system configuration.
File format
An IPYNB file is a Jupyter notebook: a JSON document holding an ordered list of cells and, unusually for a source file, the output each code cell produced. Markdown cells hold prose; code cells carry `source` as an array of lines, an `execution_count`, and an `outputs` array of stdout streams, result values, base64 images, and tracebacks, while `metadata.kernelspec` names the interpreter. The extension survives from the 2011 IPython Notebook, which became Project Jupyter in 2014.
File format
ISO is a disc-image format containing a byte-for-byte copy of an optical disc filesystem, most often ISO 9660 or UDF. It packages an entire directory tree as a single mountable image used for CDs, DVDs, and installation media. It can be mounted as a virtual drive or written to physical media.
File format
JAR (Java Archive) is a ZIP-based package that bundles Java class files, resources, and a manifest into a single distributable unit. The manifest can declare an entry point and metadata, making the JAR executable or usable as a library. It is the standard packaging format for the Java ecosystem.
File format
Java (.java) is a plain-text source file for the Java programming language — a statically typed, class-based, object-oriented language that compiles to JVM bytecode. It is widely used for enterprise back-ends, Android apps, and large systems, and emphasises explicit types and classes.
File format
A Jenkinsfile defines a Jenkins pipeline as code. Declarative pipelines wrap a `pipeline` block containing agent, environment, options, stages, and post sections, while scripted pipelines are plain Groovy using `node` and `stage` steps; both are Groovy source, so the declarative form is validated against a schema before execution. It normally lives at the repository root with no file extension.
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Julia (.jl) source files contain programs written in the Julia language, used for scientific computing with multiple dispatch and high-performance numerics.
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JPEG is a lossy raster image format based on discrete cosine transform compression, identical in encoding to files using the .jpg extension. It stores 8-bit truecolor without transparency and supports both baseline and progressive scan encodings. It is the dominant format for photographic content.
File format
JPG is the common extension for JPEG, a lossy raster format that uses discrete cosine transform compression tuned for photographic images. It is 8-bit truecolor with no alpha channel, and quality is traded against file size via a compression factor. It is ubiquitous for photos on the web and from cameras.
File format
JavaScript (.js) is a plain-text source file for the JavaScript language — the scripting language of the web, also used server-side via Node.js. It is dynamically typed and event-driven, with first-class functions, prototypes, and (in modern syntax) modules, classes, and async/await.
File format
JSON (JavaScript Object Notation) is a lightweight, text-based data-interchange format representing objects, arrays, strings, numbers, booleans, and null. It is language-independent, human-readable, and the dominant format for web APIs and configuration. It requires a single well-formed root value.
File format
JSONL (JSON Lines) is a text format where each line is a complete, independent JSON value, allowing records to be streamed and appended without parsing the whole file. It is not itself a JSON array and each line must stand alone. It is common in logging, machine learning datasets, and data pipelines.
File format
A JWT (JSON Web Token) is a compact, URL-safe token made of three base64url-encoded parts — a header, a payload of claims, and a signature — separated by dots. It is widely used to carry authentication and authorisation claims between services.
File format
A .key file holds a private key, usually PEM-encoded in PKCS#8 (BEGIN PRIVATE KEY) or a key-type-specific format. It is the secret half of a TLS or SSH identity and must normally be protected — the examples here are published, sample-only keys that must never be used in production.
File format
KML (Keyhole Markup Language) is an XML format for representing geographic features, popularized by Google Earth and Google Maps. It supports placemarks, paths, polygons, styling, and overlays with WGS84 coordinates. It is widely used for sharing annotated maps and 3D geospatial content.
File format
KMZ is a ZIP archive containing a KML document and the resources it references. The main document is stored as doc.kml at the archive root, with icons, overlay images, models, and any additional KML files alongside it, so a single file carries an entire map presentation. Google Earth and most GIS tools read KMZ and KML interchangeably.
File format
Kotlin (.kt) is a plain-text source file for the Kotlin programming language — a statically typed, JVM language from JetBrains that interoperates with Java. It is the preferred language for modern Android development and features null safety, data classes, extension functions, and concise syntax.
File format
LCOV is a plain-text code-coverage tracefile format originally produced by the Linux Test Project's front end for gcov and now emitted by tooling across many languages. Records are grouped per source file between an `SF:` line and an `end_of_record` line, with `DA:` lines giving per-line hit counts, `FN:`/`FNDA:` lines covering functions, `BRDA:` lines covering branches, and `LF`/`LH`, `FNF`/`FNH`, `BRF`/`BRH` summary counters.
File format
A .lock file pins the exact dependency graph a package manager resolved, so a later install reproduces it byte for byte. Cargo.lock and Poetry's poetry.lock use TOML, Gemfile.lock and yarn.lock use their own line-oriented grammars, and all of them record resolved versions, source registries, integrity hashes, and the transitive edges between packages. It is committed alongside the human-edited manifest, which states ranges rather than exact versions.
File format
LOG files are plain-text records of events emitted by software, typically one entry per line with a timestamp, severity, and message. There is no single standard, so formats range from unstructured text to structured JSON lines. They are central to debugging, monitoring, and auditing.
File format
LRC (.lrc) is a plain-text lyric format that pairs each line of a song with a [mm:ss.xx] timestamp so players can highlight lyrics in sync with the music. Optional ID tags at the top ([ti], [ar], [al]) carry the title, artist, and album.
File format
Lua (.lua) is a lightweight embeddable scripting language source format common in games and configuration hosts.
File format
LWO is the LightWave Object format for polygonal geometry, surfaces, vertex maps, clips, and layer data. Modern LWO files use an IFF-style FORM container with big-endian chunk identifiers and lengths; geometry is split across point, polygon, tag, and surface chunks that a reader must reconnect.
File format
LZ4 (.lz4) is an extremely fast lossless compressor optimized for speed over ratio, common in databases, filesystems, and real-time pipelines where decompression throughput matters most.
File format
M3U (.m3u) is a plain-text media playlist: a list of track paths or URLs, one per line, optionally annotated with #EXTINF duration and title directives in the extended form. It is the most widely supported playlist format across audio and video players.
File format
M3U8 (.m3u8) is a UTF-8 M3U playlist, most importantly the backbone of HTTP Live Streaming (HLS). An HLS media playlist lists timed media segments with #EXTINF tags and directives like #EXT-X-TARGETDURATION, and a master playlist points to alternate bitrate renditions.
File format
M4A is an MPEG-4 audio container, essentially an MP4 file holding audio-only content, usually AAC or sometimes Apple Lossless (ALAC). It supports rich metadata and chapters and is the standard for iTunes and Apple Music downloads. The .m4a extension signals audio-only MP4 content.
File format
M4R is an Apple ringtone format that is technically an M4A/MP4 audio file with a renamed extension recognized by iOS and iTunes as a ringtone. It contains AAC audio, typically a short clip. The distinct extension is used purely to categorize the file as a ringtone.
File format
M4S is a CMAF/fragmented-MP4 media segment: a moof header plus an mdat payload covering a few seconds of one rendition. It is not a complete file — the codec configuration lives in a separate initialisation segment, so an .m4s on its own cannot be decoded and most players will refuse it outright.
File format
M4V (.m4v) is Apple's variant of the MP4 container, typically holding H.264 video and AAC audio and sometimes carrying FairPlay DRM. Without DRM it is essentially an MP4 and plays in most players.
File format
An MBOX file is a mailbox that stores many email messages concatenated into one plain-text file, each message preceded by a 'From ' separator line. It is the classic Unix mailbox format used by many mail clients for export and archival.
File format
MBTiles is a specification for storing map tiles in a SQLite database. A metadata table records the tile set's name, format, bounds, and zoom range, and a tiles table holds one row per tile keyed by zoom_level, tile_column, and tile_row with the tile image or vector payload as a blob. Crucially, tile_row uses the TMS convention, which is flipped vertically relative to the XYZ scheme most web maps use.
File format
Markdown (MD) is a lightweight plain-text markup language that uses simple punctuation conventions to denote headings, lists, links, emphasis, and code. It is designed to be readable as-is and to convert cleanly to HTML. It is widely used for documentation, READMEs, and content authoring.
File format
A .mk file is a makefile fragment — the same syntax as a Makefile, meant to be pulled in with `include`. Rules pair a target with its prerequisites and a recipe whose lines must be indented with a literal tab, not spaces; variables are assigned with `=` (recursive), `:=` (immediate), or `?=` (conditional) and expanded with `$(...)`; and pattern rules, automatic variables such as `$@` and `$<`, and phony targets round out the language.
File format
MKV (Matroska) is an open, codec-agnostic multimedia container that holds unlimited video, audio, subtitle, chapter, and attachment tracks in one file. Its structure is EBML, a binary tree of length-prefixed elements, and its attachments typically carry the fonts an ASS subtitle track needs. Because it constrains nothing about the streams inside, the extension says nothing about whether a player can decode them. Steve Lhomme started the project in 2002; WebM is the restricted profile of it that browsers accept.
File format
An MMD file holds a Mermaid diagram written as text (diagrams-as-code): a concise syntax that describes flowcharts, sequence, class, and other diagrams which a renderer turns into an image. It is widely embedded in Markdown and documentation.
File format
MMF commonly denotes Yamaha's SMAF mobile-music format, a binary multimedia container used for ringtones and handset audio. It is organized as typed chunks that can carry score data, sampled wave data, graphics, and control information, with device-era encoding constraints unlike a general WAV or MIDI file.
File format
A MO file (.mo, Machine Object) is the compiled binary form of a gettext PO catalog used at runtime by gettext libraries. It stores msgid/msgstr pairs in a compact hashed table for fast lookup.
File format
MOBI (.mobi, Mobipocket) is a legacy Kindle e-book format based on a PDB container with compressed HTML and a limited CSS subset. Amazon retired it in favour of AZW3/KFX, but MOBI files remain widespread.
File format
An MDL Molfile (.mol) is a plain-text chemical structure format describing a single molecule: a counts line, an atom block with element symbols and 2D or 3D coordinates, and a bond block listing connections and orders. It is a core part of the SDF format and is read by nearly every cheminformatics tool.
File format
MOV is Apple's QuickTime container, introduced in 1991 and the direct ancestor of MP4. ISO adopted its box structure as the basis of ISOBMFF, so the two are close relatives rather than rivals. Beyond video and audio it carries timecode tracks, edit lists, and reference movies — files of a few kilobytes that play only where the media they point at still lives. It also carries codecs MP4 does not, notably ProRes and Animation with a true alpha channel, which keeps it the working format of professional editing.
File format
MP3 (MPEG-1 Audio Layer III) is a lossy audio format using perceptual coding to discard inaudible detail at a chosen bitrate. It is extremely widely supported and commonly carries ID3 metadata tags for title, artist, and cover art. It remains a default for music distribution and playback.
File format
MP4 (MPEG-4 Part 14) is the dominant container for digital video, holding video, audio, subtitle, and metadata tracks in a tree of typed boxes. `ftyp` declares the brand, `moov` carries the sample tables that make seeking possible, and `mdat` holds the media; when an encoder writes `moov` last, playback cannot begin until the file has fully downloaded, which a faststart remux fixes. It derives from Apple's QuickTime format, generalized by ISO into the ISOBMFF base that MOV, 3GP, and HEIF share.
File format
MPD (Media Presentation Description, .mpd) is the XML manifest at the heart of MPEG-DASH adaptive streaming. It describes periods, adaptation sets, representations, and segment templates, telling a player which bitrate ladders exist and how to construct segment URLs. It is the DASH counterpart to an HLS .m3u8 playlist.
File format
MPG (.mpg/.mpeg) is an MPEG-1/MPEG-2 program-stream container — the format of Video CDs and early digital video — multiplexing MPEG video and MP2 audio into a single stream. It is a classic legacy interchange format.
File format
MessagePack (.msgpack) is a compact binary serialization format — like JSON but smaller and faster — that encodes maps, arrays, strings, numbers, and binary blobs in a self-describing byte stream. It is popular for caching, IPC, and network protocols.
File format
An MTL file (.mtl, Material Template Library) is the companion to a Wavefront OBJ — a plain-text list of named materials with colours, specular/opacity values, and texture-map references. The OBJ links to it via an mtllib line.
File format
TypeScript (.mts) is a plain-text source file for TypeScript — a statically typed superset of JavaScript that compiles to plain JS. The .mts extension specifically marks an ES-module TypeScript file. It adds interfaces, generics, enums, and type annotations on top of JavaScript syntax.
File format
Matrix Market (.mtx) is a plain-text exchange format for sparse and dense matrices from NIST. A banner line declares the object, format, field, and symmetry — for example `%%MatrixMarket matrix coordinate real general` — comment lines follow, and then a size line gives rows, columns, and the number of stored entries. Coordinate entries list a 1-based row, a 1-based column, and a value, with symmetric matrices storing only the lower triangle.
File format
NetCDF (.nc, Network Common Data Form) is a binary, self-describing format for array-oriented scientific data. It stores multidimensional variables (like temperature over latitude, longitude, and time) with named dimensions, units, and metadata attributes, and is a standard in climate, ocean, and geoscience.
File format
NDJSON (Newline-Delimited JSON) is a streaming format where each newline-separated line is a standalone JSON object, functionally equivalent to JSON Lines. It enables incremental processing of large datasets and streaming APIs. Each record is parsed independently of the rest.
File format
Nim (.nim) source files contain programs in the Nim systems language, which compiles to C/C++/JS with Python-like syntax.
File format
An .nmea file is a log of NMEA 0183 sentences, the ASCII protocol GPS and marine electronics use. Each line begins with `$` and a five-character talker-and-type identifier such as GPGGA, GPRMC, or GPGSV, carries comma-separated fields, and ends with `*` and a two-digit XOR checksum. Positions are encoded as degrees-and-decimal-minutes with a separate hemisphere field, not as decimal degrees.
File format
NPY is NumPy's native binary format for a single array. A short header records the dtype, shape, and memory order, followed by the raw array bytes, so an array round-trips exactly without any text parsing. It is the standard way to persist embeddings, tensors, and numeric matrices in the Python data stack.
File format
Newick is a compact parenthetical notation for trees, used across phylogenetics. Nested parentheses describe the topology, commas separate siblings, names label leaves and optionally internal nodes, a colon introduces a branch length, and a semicolon terminates the tree. Internal-node labels are frequently repurposed to carry bootstrap support values, which is why a parser must not assume a label is a taxon name.
File format
OBJ (Wavefront OBJ) is a text-based 3D geometry format defining vertices, texture coordinates, normals, and faces, and referencing materials through a companion MTL file. It is simple, widely supported, and can represent polygonal meshes with UV mapping. It is a common interchange format across 3D tools.
File format
ODP is the OpenDocument Presentation format, an ISO-standardized slide-deck document stored as a ZIP archive of XML. It is the native presentation format of LibreOffice and OpenOffice Impress, storing slides, shapes, media, and notes. It is the open-standard counterpart to PPTX.
File format
ODS is the OpenDocument Spreadsheet format, an ISO-standardized spreadsheet stored as a ZIP archive of XML. It is the native spreadsheet format of LibreOffice and OpenOffice Calc, supporting multiple sheets, formulas, and formatting. It is the open-standard counterpart to XLSX.
File format
ODT is the OpenDocument Text format, an ISO-standardized word-processing document stored as a ZIP archive of XML parts. It is the native format of LibreOffice and OpenOffice Writer and stores text, styles, tables, and images. It is the open-standard counterpart to DOCX.
File format
OFF (.off, Object File Format) is a simple ASCII 3D mesh format: a header, vertex and face counts, then a list of vertex coordinates and polygon indices. Its minimalism makes it a common teaching and geometry-processing format.
File format
OGG is a free open container format from Xiph, most commonly holding Vorbis-encoded lossy audio but also able to carry Opus, FLAC, or Theora video. It supports streaming, metadata, and multiple logical streams. It is widely used in games and open-source software.
File format
OGV is the video variant of the Ogg container, typically carrying Theora video with Vorbis or Opus audio in a free, open format. It was an early royalty-free option for HTML5 video before WebM and MP4 became dominant. It is now used mainly for open-format compatibility.
File format
ONNX (Open Neural Network Exchange) is a portable, protobuf-based graph format for machine-learning models. It records typed inputs and outputs, tensor initializers, operators, attributes, and an opset version so inference runtimes can exchange a model without sharing its training framework.
File format
OPML (Outline Processor Markup Language, .opml) is an XML format for nested outlines. Its most common use is exchanging feed subscription lists between RSS readers, where each outline element carries a feed title and xmlUrl, but it also serves for mind maps and document outlines.
File format
Opus is a highly efficient lossy audio codec standardized by the IETF, excelling across low-latency speech and high-quality music at a wide range of bitrates. Files typically use an Ogg container. It is the default audio codec for WebRTC and much modern streaming.
File format
Apache ORC (Optimized Row Columnar, .orc) is a binary columnar format from the Hadoop ecosystem. It stores data in stripes with lightweight indexes, per-column compression, and embedded statistics, and is common in Hive and big-data pipelines.
File format
An .osm file holds OpenStreetMap data in the project's XML schema. The document contains node, way, and relation elements, each with an id, version, and free-form tag children; ways reference their nodes in order, and relations reference members by type, id, and role. It is the format returned by the OSM API and by Overpass queries, and the input to most OSM-based routing and rendering toolchains.
File format
OTF (OpenType Font) is a scalable font format built on the TrueType structure but able to carry PostScript/CFF cubic-Bezier outlines and advanced typographic features like ligatures and alternates. It supports large Unicode glyph sets and rich layout tables. It is a professional-grade format for desktop and web.
File format
OpenTimelineIO (OTIO) is an open editorial interchange model for timelines, tracks, clips, transitions, gaps, markers, and external media references. Its JSON serialization stores schema-labelled objects and rational time values while adapters translate the same timeline model to and from application-specific formats.
File format
A .p12 file is a PKCS#12 (PFX) bundle — a password-protected binary archive that packages a certificate together with its private key (and optionally a chain) in one importable file. It is the standard way to move a complete TLS or client identity between systems.
File format
Apache Parquet (.parquet) is a binary, columnar storage format for analytical data. It stores each column separately with per-column compression and encoding, embeds a schema and statistics, and is the de-facto standard for data lakes and engines like Spark, DuckDB, and pandas/pyarrow.
File format
A .patch file is a unified diff packaged for transmission, most often as produced by `git format-patch`. Beyond the diff itself it carries an email-style header with the author, date, and commit subject, a commit message body, per-file `diff --git` headers recording renames and mode changes, and hunk headers of the form `@@ -old,count +new,count @@`. Applying it reconstructs a specific change against a specific before-state.
File format
A .pb file holds Protocol Buffers binary data — Google's compact, schema-driven serialization where field numbers and wire types encode the message. Without the matching .proto schema the bytes are opaque, which makes it efficient but not self-describing.
File format
PBM (Portable Bitmap) is the simplest Netpbm format, storing 1-bit black-and-white images as ASCII or packed binary bits after a short text header. It uses no compression and represents each pixel as a single on or off value. It is used for bilevel masks and toolchain intermediates.
File format
A PDB file (.pdb, Protein Data Bank format) is a plain-text format for 3D molecular structures, using fixed-column ATOM and HETATM records for atom coordinates plus CONECT records for bonds. It is the classic format for proteins and small molecules in structural biology.
File format
PDF (Portable Document Format) is a page-oriented format that fixes layout, fonts, and vector and raster graphics so a page renders identically anywhere. A `%PDF-` header is followed by numbered objects, a cross-reference table mapping each to a byte offset, and a trailer; edits append incremental updates rather than rewrite the file. Page content is a stream of drawing operators, so a PDF holds no words or paragraphs, only positioned glyph runs. Adobe released it in 1993 and gave it to ISO as ISO 32000-1 in 2008.
File format
PEM (Privacy-Enhanced Mail) is a text container that Base64-encodes DER binary data between BEGIN/END header lines, used to hold X.509 certificates, certificate requests, and keys. A single .pem file may contain a certificate, a chain, or a private key, which makes it the most common format for TLS material.
File format
PGM (Portable Graymap) is a Netpbm-family format storing single-channel greyscale images as ASCII or raw binary values with a simple text header. It uses no compression and supports 8- or 16-bit gray levels. It is frequently used in image processing and computer vision.
File format
PHP (.php) is a plain-text source file for the PHP language — a dynamically typed, server-side scripting language designed for web development, embeddable in HTML. Modern PHP supports classes, namespaces, type declarations, and closures, and powers a large share of web back-ends and CMS platforms.
File format
PLY (.ply, Polygon/Stanford Triangle Format) is a flexible 3D format storing a list of vertices and faces with arbitrary per-element properties (position, colour, normals, confidence), in ASCII or binary. It is standard for scanned meshes and point clouds.
File format
PNG (Portable Network Graphics) is a raster image format using lossless DEFLATE compression. It supports full 8- or 16-bit-per-channel truecolor, palette, and greyscale modes with an optional alpha channel, but no animation. It is the standard choice for screenshots, logos, and graphics with sharp edges or transparency.
File format
A PO file (.po, Portable Object) is a gettext translation catalog: a plain-text list of msgid (source string) and msgstr (translation) pairs, with a header defining the language and plural rules, source-location comments, and support for plural forms. It is the working file translators edit and is compiled to a binary .mo for runtime.
File format
A POT file (.pot, Portable Object Template) is a gettext template — a PO file with all msgstr values left empty. It is generated from source code by string extraction (xgettext) and is copied to start a new language's .po translation. Its header carries the plural-forms rule and project metadata.
File format
PPM (Portable Pixmap) is a deliberately simple truecolor image format from the Netpbm family, storing RGB pixels as either ASCII text or raw binary after a small text header. It uses no compression, making files large but trivial to parse. It is common in academic, scientific, and toolchain contexts.
File format
A .ppt file is the legacy binary Microsoft PowerPoint format (97–2003) built on the OLE2 compound-file structure, distinct from the modern .pptx. Legacy decks and templates still use it.
File format
PPTX is the default Microsoft PowerPoint format, an Office Open XML presentation packaged as a ZIP archive of slide XML, layouts, media, and themes. It stores slides, shapes, text, images, and speaker notes. It is the standard for editable slide decks.
File format
A .prj file is the coordinate-reference-system sidecar of an Esri shapefile. It contains a single line of Well-Known Text describing the CRS: for a projected system, the projection method, its parameters, the linear unit, and the geographic system it is based on; for a geographic system, the datum, spheroid, prime meridian, and angular unit. Without it a shapefile's coordinates are just numbers.
File format
A .prom file holds metrics in the Prometheus text exposition format, the same body a `/metrics` endpoint returns. Each metric family is introduced by `# HELP` and `# TYPE` comments and followed by one sample per line: a metric name, an optional brace-delimited label set, a value, and an optional millisecond timestamp. Counters, gauges, histograms (with `_bucket`, `_sum`, `_count` series and a `+Inf` bucket), and summaries with quantile labels all use this one grammar.
File format
A .properties file is the Java configuration format: one `key=value` or `key:value` pair per line, with `#` or `!` comments, backslash line continuations, and escapes for spaces, colons, and equals signs inside keys. Keys are conventionally dot-separated to imply hierarchy, though the format itself is flat. In its original definition the file is ISO-8859-1 with `\uXXXX` escapes for anything else; modern Java tooling also reads UTF-8.
File format
Proto files define Protocol Buffers schemas, Google's language-neutral interface definition language for serializing structured data. They declare typed messages, fields, and services that a compiler turns into efficient binary serialization code in many languages. They underpin gRPC and high-performance data interchange.
File format
A .pub file holds an SSH public key in the single-line OpenSSH format — an algorithm name (such as ssh-ed25519), a Base64-encoded key blob, and an optional comment. It is the shareable half of an SSH key pair, added to a server's authorized_keys to grant access.
File format
A PUML file contains a PlantUML diagram written as text — sequence, class, use-case, activity, and other UML diagrams described in a compact syntax that PlantUML renders to an image. It is a popular diagrams-as-code format.
File format
Python (.py) is a plain-text source file for the Python programming language — a dynamically typed, indentation-structured language widely used for scripting, data science, web back-ends, and automation. A .py file is compiled to bytecode and run by the Python interpreter.
File format
R (.r / .R) source files contain scripts for the R statistical computing language, including data frames and tidy pipelines.
File format
RAR is a proprietary archive format with several on-disk generations, solid compression, optional recovery records, encryption, split volumes, and Unicode names. Readers identify its signature and version before walking headers and compressed data; support for one generation does not guarantee support for another.
File format
Ruby (.rb) is a plain-text source file for the Ruby programming language — a dynamically typed, object-oriented scripting language known for expressive, readable syntax and blocks. Everything is an object, and it is widely used for web development (Rails), scripting, and automation.
File format
.resx is a .NET XML resource file that stores localizable strings (and other resources) as name/value data elements, with a standard header block declaring the ResX schema and reader/writer types. Per-culture files like Resources.es.resx provide translations that the .NET runtime resolves by culture.
File format
RIS is a plain-text citation format using two-letter tags (TY for type, AU for author, TI for title, PY for year) with each record ending in an ER tag. It is widely supported by reference managers and publisher databases for importing and exchanging citations.
File format
RM is the RealMedia container developed for early streaming audio and video. A file consists of typed objects for the file header, properties, media streams, content metadata, packet data, and an optional index; the contained RealAudio or RealVideo codecs are separate from the container and are rarely browser-playable today.
File format
A .robot file is a Robot Framework test suite written in the framework's plain-text tabular syntax. Sections introduced by headers such as *** Settings ***, *** Variables ***, *** Test Cases ***, and *** Keywords *** hold library imports, variable definitions, keyword-driven test cases, and user-defined keywords, with arguments separated by two or more spaces. Tags, documentation, setup, and teardown are declared inline as settings.
File format
Rust (.rs) is a plain-text source file for the Rust programming language — a statically typed, compiled systems language focused on memory safety without a garbage collector, enforced by its ownership and borrow checker. It features enums with data, pattern matching, traits, generics, and a strong type system.
File format
RSS (Really Simple Syndication) is an XML-based web feed format that publishes a channel of items with titles, links, descriptions, and publication dates. It lets readers and aggregators track updates to blogs, news, and podcasts. It is a long-established syndication standard.
File format
reStructuredText (reST) is a plain-text markup language from the Python community, used heavily for software documentation and by the Sphinx documentation generator. It uses indentation and simple punctuation for structure — headings, directives, roles, and cross-references. The .rst extension is standard.
File format
RTF (Rich Text Format) is a plain-text-based document format that encodes styling, fonts, and layout using backslash control words. It is human-readable in a text editor and broadly interoperable across word processors. It predates Office Open XML and remains a portable rich-text interchange format.
File format
safetensors is a simple, safe binary format for storing model weights. An 8-byte length precedes a JSON header that maps each tensor name to its dtype, shape, and byte offsets, followed by the raw tensor data — with no executable code, unlike Python pickles. It has become a common format for sharing model checkpoints.
File format
SAM (Sequence Alignment/Map) is the plain-text format for sequence alignments and the human-readable counterpart of binary BAM. An optional header of `@`-prefixed lines declares the sort order and reference sequences, and each alignment line has eleven mandatory tab-separated fields — including a bitwise FLAG, a 1-based position, a CIGAR string describing the match, and the sequence and its qualities — followed by optional typed TAG:TYPE:VALUE fields.
File format
SBV (.sbv) is the simple caption format used by YouTube's Studio. Each cue is a start,end timestamp line (H:MM:SS.mmm) followed by the caption text, with a blank line between cues. It has no styling — just timings and text.
File format
Scala (.scala) is a plain-text source file for Scala — a JVM language combining object-oriented and functional styles, with case classes, pattern matching, and a powerful type system.
File format
SCC (Scenarist Closed Captions, .scc) is the broadcast interchange format for CEA-608 captions. Each line is an SMPTE timecode followed by pairs of hexadecimal bytes that are the literal 608 control codes and characters, so caption positioning, roll-up versus pop-on style, and italics are all encoded as byte pairs rather than as markup. It is plain ASCII, but it is not human-readable prose.
File format
SDF (Structure-Data File) is MDL's multi-record chemistry format. Each record is a molfile — a counts line, an atom block, and a bond block — followed by tagged data fields written as `> <NAME>` lines with their values, and terminated by a `$$$$` delimiter. It is how compound libraries with per-molecule properties are shipped between cheminformatics tools.
File format
A shell script (.sh) is a plain-text program for a Unix shell such as bash — a sequence of commands with variables, conditionals, loops, functions, and pipelines. Scripts start with a shebang line (like #!/usr/bin/env bash) and are used for automation, builds, and system administration.
File format
The .shp file is the geometry component of an Esri shapefile. It stores a fixed 100-byte header followed by variable-length records, each holding one point, polyline, polygon, or multipoint feature as raw little-endian doubles. It is never usable alone: a shapefile is a set of sidecar files, minimally .shp with a .shx index and a .dbf attribute table, and usually a .prj holding the coordinate reference system.
File format
The .shx file is the positional index of an Esri shapefile. It repeats the .shp header and then stores one fixed 8-byte record per feature, giving the byte offset and content length of that feature in the .shp file, so a reader can seek directly to feature N instead of scanning from the start.
File format
A .smi file holds SMILES strings — a line notation that encodes a molecular graph as text. Atoms are written as element symbols, aromatic atoms in lower case, bonds as `-`, `=`, `#`, branches in parentheses, and rings as matching digit labels, with stereochemistry expressed by `/`, `\\`, and `@` markers. Files typically carry one SMILES per line with an optional whitespace-separated identifier, and a canonical SMILES is a unique string for a given structure.
File format
An .spdx file is an SPDX software bill of materials written in the specification's tag-value serialisation: plain-text `Tag: value` lines grouped into a document-creation block, one block per package, and optional file and relationship blocks. It records the document namespace and licence, package names, versions, suppliers, download locations, verification codes, declared and concluded licences, and the relationships that connect packages to each other.
File format
SQL files contain plain-text Structured Query Language statements, typically schema definitions, data inserts, or queries used to build or populate a database. Dialect details vary between engines such as PostgreSQL, MySQL, and SQLite. A dump file often recreates an entire database when executed.
File format
SQLite is a self-contained, serverless relational database stored as a single binary file holding tables, indexes, and schema in a defined page format. It is the most widely deployed database engine, embedded in browsers, phones, and applications. The file is a complete, transactional SQL database requiring no server.
File format
SRT (SubRip) is a plain-text subtitle format listing numbered cues, each with a start and end timecode and one or more lines of text. It is simple, human-readable, and extremely widely supported by players. It carries no styling metadata beyond basic inline tags.
File format
SSA (SubStation Alpha, .ssa) is the predecessor of ASS — a styled subtitle format with a Script Info header, a styles section, and timed Dialogue events. It supports fonts, colours, and positioning, and remains widely readable even though ASS has largely replaced it.
File format
STEP (Standard for the Exchange of Product model data) is an ISO 10303 CAD format that stores precise boundary-representation solid geometry and product data as structured text. Unlike mesh formats, it preserves exact curves and surfaces for engineering use. It is the leading neutral format for mechanical CAD interchange.
File format
STL (Stereolithography) is a 3D model format that represents a surface as an unstructured collection of triangular facets, each with a normal and three vertices. It stores only geometry with no color, texture, or units, and comes in ASCII and binary variants. It is the workhorse format for 3D printing.
File format
An Apple .strings file is a plain-text localization catalog used by iOS and macOS apps. Each line maps a quoted key to a quoted translated value with a trailing semicolon, optionally preceded by a comment, and placeholders use printf-style tokens like %@ and %d. It is typically stored per-locale in an .lproj folder.
File format
SVG (Scalable Vector Graphics) is an XML-based vector image format describing shapes, paths, text, and styling that scale losslessly to any resolution. It can embed CSS, scripting, and references, so it is both an image and an executable document. It is standard for icons, diagrams, and resolution-independent web graphics.
File format
Swift (.swift) is a plain-text source file for the Swift programming language — a statically typed, compiled language from Apple used for iOS, macOS, and server development. It emphasises safety with optionals and value types, and features structs, protocols, generics, and pattern matching.
File format
TAP (Test Anything Protocol) is a line-based plain-text format for reporting test results. A stream declares a plan such as `1..12` and then emits one `ok` or `not ok` line per test, optionally with a description, a `# SKIP` or `# TODO` directive, and an indented YAML block carrying diagnostic detail. It is deliberately simple enough that a test runner in any language can emit it and a harness can parse it line by line.
File format
TAR (Tape Archive) is a Unix archive format that concatenates files with their metadata into a single uncompressed stream of fixed-size blocks. It preserves permissions, ownership, and directory structure but applies no compression itself. It is usually paired with a compressor such as gzip or xz.
File format
TAR.BZ2 is a tar archive compressed as one bzip2 byte stream. The canonical compound suffix describes both layers; .tbz2 is a common alias for the same bytes. A converter must finish bzip2 decoding before it can validate tar headers, member paths, padding, and archive termination.
File format
TAR.XZ is a tar archive wrapped in an XZ stream, normally using LZMA2 compression. The .txz alias refers to the same layered format; XZ supplies stream checks and an index, while tar supplies filenames, metadata, member boundaries, and directory structure.
File format
TAR.ZST combines a POSIX tar member stream with Zstandard compression. The outer Zstandard frame must be decompressed before 512-byte tar headers, file payloads, padding, checksums, and end blocks can be interpreted; concatenated frames and long-path extensions make robust implementations treat compression and archive parsing as separate stages.
File format
TBZ2 is a shorthand extension for a TAR archive compressed with bzip2, equivalent to .tar.bz2. The tar step bundles files and metadata, then bzip2 compresses the combined stream for a higher ratio. It is used for distributing larger source and data archives.
File format
TeX/LaTeX is a plain-text typesetting language widely used for scientific and technical documents. A .tex source file describes structure (sections, lists, tables), mathematics, and references with markup commands, and a TeX engine compiles it — usually to PDF. It is the standard in mathematics, physics, and academic publishing.
File format
A .tf file is a Terraform configuration written in HCL. It declares infrastructure as blocks — terraform, provider, resource, data, variable, output, module, locals — whose bodies hold arguments and nested blocks, with values drawn from expressions, interpolation, and functions. Terraform reads every .tf file in a directory as one merged configuration, so ordering across files carries no meaning.
File format
A .tfvars file supplies values for the variables a Terraform configuration declares. It uses the same HCL grammar but permits only top-level `name = value` assignments — strings, numbers, booleans, lists, and objects — with no blocks or expressions. Files named terraform.tfvars or *.auto.tfvars are loaded automatically; others must be passed explicitly.
File format
TGA (Truevision Targa) is a raster format supporting 8- to 32-bit pixels with optional run-length encoding and an alpha channel. Long used in video, gaming, and 3D texturing, it stores simple uncompressed or RLE-compressed image data. It remains common as a texture and intermediate format.
File format
TGZ is a shorthand extension for a TAR archive compressed with gzip, equivalent to .tar.gz. The tar step bundles files and metadata, then gzip compresses the whole stream. It is one of the most common distribution formats for Unix software and datasets.
File format
TIFF (Tagged Image File Format) is a flexible container that stores one or more raster images with a rich tag-based header describing layout, compression, and color. It supports uncompressed, LZW, and other codecs, high bit depths, multiple pages, and CMYK, making it common in publishing, scanning, and archival workflows. Its flexibility means reader support varies.
File format
TMX (Translation Memory eXchange) is an XML standard for exchanging translation-memory segments between CAT tools. A TMX file holds translation units with aligned source and target segments plus metadata.
File format
TOML (Tom's Obvious Minimal Language) is a configuration format designed to be unambiguous and easy to read, with typed values, sections in bracketed tables, and clear date and number handling. It maps cleanly to hash tables. It is widely used for application and package configuration, such as Rust's Cargo and Python's pyproject.
File format
TopoJSON is an extension of GeoJSON that encodes topology. Shared boundaries are stored once as arcs and referenced by the geometries that use them, coordinates are quantised to an integer grid and delta-encoded, and a transform object records the scale and translation needed to recover real positions. For data with many adjacent polygons — administrative boundaries especially — files are dramatically smaller than the equivalent GeoJSON.
File format
TRX is the XML test-result format produced by the Visual Studio test platform and `dotnet test`. A TestRun element carries run metadata, a Times element with creation, queuing, start, and finish timestamps, a TestDefinitions section describing each test method, and UnitTestResult entries recording outcome, duration, output, and any error message and stack trace. A ResultSummary element aggregates the counts.
File format
TS (.ts) is an MPEG transport stream — the container used for broadcast and HTTP Live Streaming segments — carrying packetized, timestamped MPEG video/audio in fixed 188-byte packets designed to survive transmission errors. (This .ts is video, not TypeScript.)
File format
TSV (Tab-Separated Values) is a plain-text tabular format like CSV but using tab characters as field delimiters. Because tabs rarely appear in data, it often needs less quoting than CSV. It is common in bioinformatics, logs, and command-line data workflows.
File format
A TrueType Collection (.ttc) is a single file that bundles several related fonts, sharing common tables (like glyph outlines) to save space. It is used to ship font families or CJK fonts with many variants in one file. A font index selects which face inside the collection to use.
File format
TTF (TrueType Font) is a scalable outline font format developed by Apple and Microsoft that uses quadratic Bezier curves and includes hinting for sharp rendering at small sizes. It stores glyph outlines, metrics, and character mappings in a single file. It is one of the most widely supported desktop and web font formats.
File format
TTML (Timed Text Markup Language, .ttml, also called DFXP) is a W3C XML format for timed text and captions. It wraps timed paragraphs in a tt document with styling and layout regions, and underlies broadcast and streaming caption profiles like IMSC, SMPTE-TT, and EBU-TT.
File format
TXT is a plain-text file containing unformatted character data with no styling or structure beyond line breaks. Its interpretation depends on character encoding, most commonly UTF-8, and on line-ending convention. It is the most universal and portable text container.
File format
TXZ is a shorthand extension for a TAR archive compressed with xz (LZMA2), equivalent to .tar.xz. The tar step bundles files, then xz compresses the stream at a high ratio with integrity checking. It is common for Linux packages and large software releases.
File format
USDZ (.usdz) is Apple's zipped Universal Scene Description package — an uncompressed ZIP bundling a USD scene with its textures — used for AR Quick Look on iOS. USD itself is Pixar's scene-composition standard for film and 3D.
File format
VCF (vCard) is a plain-text format for electronic business cards, storing contact details like names, phone numbers, emails, and addresses as property lines within BEGIN and END VCARD blocks. Multiple vCards can be concatenated in one file. It is the standard for contact exchange across devices.
File format
VOX is MagicaVoxel's chunked binary voxel-scene format. A VOX header and version are followed by a MAIN container whose SIZE, XYZI, RGBA, palette, transform, group, and shape chunks describe voxel models and optional scene hierarchy using little-endian integers.
File format
The legacy VTK file format stores scientific visualization datasets such as polygonal meshes, structured grids, and unstructured grids in a compact header plus ASCII or binary data sections. DATASET selects the topology, while POINTS, CELLS, POLYGONS, and attribute blocks describe geometry and associated scalar or vector values.
File format
WebVTT (VTT) is the W3C subtitle and caption format used by the HTML5 <track> element for timed text on the web. It extends the SubRip model with cue settings, positioning, styling, and metadata, and requires a WEBVTT header. It is the standard format for browser-based captions.
File format
A WARC (Web ARChive) file stores one or more web resources — requests, responses, and metadata — concatenated as records with headers, in the standard format used by web crawlers and archives such as the Wayback Machine.
File format
WAV (Waveform Audio) is a RIFF-based container that typically holds uncompressed linear PCM audio, though it can wrap other codecs. Because samples are stored raw, files are large but lossless and simple to read, with configurable sample rate, bit depth, and channel count. It is the standard format for high-fidelity and intermediate audio.
File format
WebM is a deliberately narrow profile of Matroska, restricted to codecs anyone may implement royalty-free. It keeps Matroska's EBML structure but permits only VP8, VP9, or AV1 video with Vorbis or Opus audio, which is what made it the open counterpart to MP4 in an HTML5 `<video>` element. Google announced it at I/O in 2010 alongside the newly open-sourced VP8 and added VP9 and Opus in 2013. That restriction is also its limit: a WebM cannot carry H.264 or AAC at all.
File format
A web app manifest (.webmanifest) is a JSON file that describes a Progressive Web App to the browser, declaring its name, icons, theme colors, start URL, and display mode. It enables installation to a device home screen and standalone launching. It is linked from HTML via a manifest link element.
File format
WebP is a modern raster format from Google offering both lossy (VP8-based) and lossless compression, with alpha transparency and animation support. It typically produces smaller files than JPEG or PNG at comparable quality. It is widely supported by current browsers.
File format
WKT (Well-Known Text) is the OGC's human-readable encoding for geometry and for coordinate reference systems. Geometry WKT spells out a type and its coordinates — POINT, LINESTRING, POLYGON, and their MULTI and GEOMETRYCOLLECTION forms — while CRS WKT nests PROJCS, GEOGCS, DATUM, and PARAMETER clauses. Its binary counterpart, WKB, encodes the same geometry model compactly.
File format
WMA (Windows Media Audio) is a Microsoft lossy audio format stored in the ASF container, developed as a competitor to MP3. It supports several profiles including lossless and voice variants and historically carried DRM. It is a legacy Windows-ecosystem format with limited cross-platform support.
File format
WMV (.wmv, Windows Media Video) is Microsoft's video format inside the ASF container, pairing WMV/VC-1 video with WMA audio. It was ubiquitous on Windows and still appears in legacy corporate media.
File format
WOFF (Web Open Font Format) wraps TrueType or OpenType font data with compression and metadata specifically for efficient delivery over the web. It reduces download size and is recognized by all modern browsers via CSS @font-face. It is essentially a web-optimized container around an existing font.
File format
WOFF2 is the successor to WOFF, using Brotli compression to shrink web fonts substantially further than the original format. It wraps TrueType or OpenType outlines for efficient browser delivery and is the preferred modern web font format. It offers the smallest sizes with broad current-browser support.
File format
VRML (.wrl, Virtual Reality Modeling Language) is a text-based format for 3D scenes and worlds — nodes for geometry, materials, lighting, and interaction — that powered early web 3D before X3D and glTF. It remains a legacy interchange format.
File format
X3D (.x3d) is the XML-based successor to VRML — an ISO standard for interactive 3D scenes with geometry, appearance, animation, and scripting. It is used in web 3D, scientific visualization, and archival.
File format
XFDF (XML Forms Data Format) is the XML representation of PDF form data — the modern, human-readable successor to binary FDF. It records each field name and value as XML elements and references the source PDF, making it easy to generate, diff, and transform with standard XML tooling. It is widely used to pre-fill and extract data from AcroForm PDFs.
File format
.xlf is a common file extension for XLIFF, the OASIS XML Localization Interchange File Format — identical in content to .xliff. It carries translatable source and target segments with metadata for exchange between localization tools, and is frequently the extension emitted by Angular and Symfony toolchains.
File format
XLIFF (XML Localization Interchange File Format) is an OASIS-standard XML format for exchanging translatable content between tools. It wraps source and target text in trans-units (1.2) or units and segments (2.0), with metadata, states, and notes. It is the lingua franca between authoring tools and translation-management systems.
File format
XLS is the legacy Microsoft Excel format using the binary BIFF structure inside an OLE2 compound file, superseded by XLSX in 2007. It stores worksheets, formulas, and formatting in a binary layout rather than XML. It remains common in older systems and exports.
File format
XLSX is the default Microsoft Excel format, an Office Open XML spreadsheet stored as a ZIP archive containing worksheet XML, shared strings, styles, and formulas. It supports multiple sheets, cell formatting, charts, and calculated values. It is the standard for editable tabular workbooks.
File format
XML (Extensible Markup Language) is a verbose, self-describing markup language using nested tags, attributes, and namespaces to represent structured, hierarchical data. It supports schemas, entities, and validation and underlies many document and data formats. It remains common in enterprise, publishing, and interchange contexts.
File format
The XYZ format is the simplest way to write a molecular geometry: a first line giving the atom count, a free-form comment line, and then one line per atom with an element symbol and Cartesian x, y, and z coordinates in ångströms. It records no bonds, charges, or connectivity. Multi-frame files simply concatenate blocks, which is how trajectories are stored.
File format
XZ is a file compressed with the LZMA2 algorithm in the XZ container, offering very high compression ratios with integrity checking. It compresses a single stream and is often used to compress tar archives. It is common for software distribution and Linux packages.
File format
YAML (YAML Ain't Markup Language) is a human-readable data-serialization format using indentation, key-value pairs, and lists, and is a superset of JSON. It supports comments, anchors, and multiple documents per file, favoring readability for configuration. Its indentation sensitivity makes it error-prone to hand-edit.
File format
YML is an alternate file extension for YAML, a human-readable data-serialization format based on indentation, key-value mappings, and lists. The content and parsing rules are identical to .yaml; only the extension differs. It is widely used for CI and application configuration files.
File format
Zig (.zig) is a plain-text source file for the Zig systems language — a C alternative focused on simplicity, manual memory control, and comptime metaprogramming.
File format
ZIP is a widely supported archive format that bundles multiple files and directories into one container, typically with per-file DEFLATE compression and a central directory index. It supports random access to individual entries without decompressing the whole archive. It underlies many document formats such as DOCX and EPUB.
File format
Zstandard (.zst) is a modern, fast lossless compressor offering high ratios with very fast decompression and tunable levels. It is widely used in package managers, filesystems, and data pipelines.
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