Structured Log — Multi-Line Stack Traces Inside JSON (jsonl)
Java, Python and Go stack traces carried inside JSON string fields with their newlines escaped — the shape a structured logger produces, and the one that defeats multi-line joining rules written for plain text. Includes a Caused by chain and a goroutine dump.
{"ts":"2026-03-17T09:14:33.090Z","level":"info","service":"checkout-api","msg":"handling request","request_id":"req-000001"}
{"ts":"2026-03-17T09:14:33.270Z","level":"error","service":"checkout-api","msg":"unhandled exception while processing request","request_id":"req-000001","error":{"type":"java.lang.IllegalStateException","message":"java.lang.IllegalStateException: cart 9f31a7 has no priced line items","stack":"java.lang.IllegalStateException: cart 9f31a7 has no priced line items\n\tat com.example.shop.checkout.PricingService.total(PricingService.java:142)\n\tat com.example.shop.checkout.OrderService.place(OrderService.java:88)\n\tat com.example.shop.checkout.OrderController.create(OrderController.java:54)\n\tat java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)\nCaused by: java.util.NoSuchElementException: no price row for sku SKU-88213\n\tat com.example.shop.catalog.PriceRepository.require(PriceRepository.java:67)\n\t... 12 more","frames":8}}
{"ts":"2026-03-17T09:14:33.360Z","level":"warn","service":"checkout-api","msg":"request failed, returning 500","request_id":"req-000001"}
{"ts":"2026-03-17T09:14:33.600Z","level":"info","service":"payments-api","msg":"handling request","request_id":"req-000004"}
{"ts":"2026-03-17T09:14:33.780Z","level":"error","service":"payments-api","msg":"unhandled exception while processing request","request_id":"req-000004","error":{"type":"shop.payments.errors.UpstreamTimeout","message":"Traceback (most recent call last):","stack":"Traceback (most recent call last):\n File \"/srv/payments/handlers/authorize.py\", line 118, in authorize\n charge = psp.create_charge(token, amount_minor, currency)\n File \"/srv/payments/psp/client.py\", line 141, in _post\n raise UpstreamTimeout(f\"{path} exceeded {timeout}s\")\nshop.payments.errors.UpstreamTimeout: /v1/charges exceeded 2.0s","frames":6}}
{"ts":"2026-03-17T09:14:33.870Z","level":"warn","service":"payments-api","msg":"request failed, returning 500","request_id":"req-000004"}
{"ts":"2026-03-17T09:14:34.110Z","level":"info","service":"inventory-api","msg":"handling request","request_id":"req-000007"}
{"ts":"2026-03-17T09:14:34.290Z","level":"error","service":"inventory-api","msg":"unhandled exception while processing request","request_id":"req-000007","error":{"type":"runtime.panic","message":"panic: reserve: sku SKU-88213 not found","stack":"panic: reserve: sku SKU-88213 not found\n\ngoroutine 41 [running]:\ngithub.com/example/shop/inventory.(*Reserver).Reserve(0xc0000b4000, {0xc0001a2000, 0x3})\n\t/src/inventory/reserve.go:88 +0x1a4\ngithub.com/example/shop/inventory.handleReserve({0x8f2c40, 0xc0000f6000}, 0xc0001b8100)\n\t/src/inventory/http.go:41 +0xc8","frames":7}}
{"ts":"2026-03-17T09:14:34.380Z","level":"warn","service":"inventory-api","msg":"request failed, returning 500","request_id":"req-000007"}
Specifications
- Lines
- 9
- Error Records
- 3
- Languages
- Java, Python, Go
- Stack Newlines Escaped
- true
- Has Caused By
- true
- Has Goroutine Dump
- true
- Longest Stack Lines
- 8
Testing contract
Expected to pass- Scenario
- Parse the records and render each stack trace over multiple lines.
- Expected result
- Nine records parse as nine JSON documents, and each error.stack field unescapes to a trace of 6 to 8 lines with its Caused by and goroutine sections intact.
What is a .jsonl file?
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.
How to use this file
Use an example JSONL to test line-by-line streaming parsers, append-and-resume ingestion, and batch pipelines that process one record per line.
How to use this file for testing
“Structured Log — Multi-Line Stack Traces Inside JSON (jsonl)” is a deterministic Novus Examples fixture for Observability, Log parsing, Error handling. Structured and plain-text telemetry with known timestamps, levels, request identifiers, and error states for testing log ingestion, correlation, dashboards, and alert pipelines.
Documented properties for this file: JSONL · 2,894 bytes. Compare results against paired or grouped companions on this page when present (clean↔damaged, searchable↔scanned, or format twins) so scores stay reproducible across runs.
Download the file once, keep the path stable in CI or local scripts, and treat the spec table as the contract: dimensions, seeds, field lists, and roles are intentional. Corrupt or invalid samples are labelled as such — expect parsers to fail loudly rather than silently accept them.
Telemetry fixtures use fixed trace IDs, span IDs, and timestamps so ingestion is reproducible run to run. Point your collector, parser, or query layer at the file and assert the documented span tree, metric families, or severity mix; service and host names are invented.
Code examples
import json
with open("app-multiline-stacktraces.jsonl") as f:
rows = [json.loads(line) for line in f]
print(len(rows), rows[0])Related files
- log.NET Exception with an Inner Exception Chain (log)A .NET exception whose inner exception is introduced by the ---> marker and closed by End of inner exception stack trace, wrapped in pipe-delimited log lines. Error groupers that key on the outermost message alone merge two genuinely different faults here.
- logGo Panic with Full Goroutine Dump (log)A Go panic followed by the runtime's full goroutine dump — four goroutines with their wait states, two-line frames and a created by attribution, separated by blank lines. Blank-line separation defeats multi-line rules that treat an empty line as the end of an event.
- logPlain-Text Log — Multi-Line Events Needing Line Joining (log)A Spring-style text log where two stack traces span many physical lines. Eight logical events across a larger number of lines, so a shipper's multi-line rule — anything not starting with a timestamp continues the previous event — can be scored against a known answer.
- logPlain-Text Log — No Trailing Newline on the Last Line (log)Four log lines where the last has no terminating newline — the normal state of any file still open for append. A tailer that only emits on seeing a newline holds that fourth line forever, which is why the newest error is the one missing from the dashboard.
- logRust Panic with Numbered Backtrace (log)A Rust panic surrounded by ordinary tracing output: the panic location with line and column, a six-frame numbered backtrace where every frame spans two lines, and the RUST_BACKTRACE note. Frame numbering and the deep indent are what a generic stack parser gets wrong here.
- jsonlStructured Log — Clock Skew Across Three Hosts (jsonl)Three hosts writing to one stream with disagreeing clocks: one 45 seconds behind and one six hours ahead because NTP is unreachable. Interleaved by host, so a naive tail shows events from the future and a retention window silently drops the past.
Generated by generation/observability.py. Free for any use, no attribution required — license.