TRACE.JSON
Generated by scripts/gen-format-pages.py from docs/data/format-metadata/, FILE_FORMATS.csv and docs/formats-master.csv. Do not edit by hand: change the source, then run the script.
Chrome Trace Preview.
At a glance
| Purpose | A Chrome trace-event JSON file: a list of timeline events (durations, instants, counters, metadata) from Chrome or Perfetto. |
| Extensions | .trace.json |
| Poka parser | poka-trace-event |
| Viewer | poka-tree-viewer |
| Depth tier | Parser with a shared viewer (see Depth tiers) |
| Breadth tier | B4 Summary (see Breadth tiers) |
How much Poka reads
B4 Summary. The container and metadata are read and summarised (counts, properties, structure), but the main content is not rendered.
Confidence: medium (the reviewer read the code). Basis: Reviewed 2026-10-26: read parsers/poka-trace-event/src/main.rs (436 lines) and plugin.json. No unit tests or tests/samples.rs; the corpus has no .trace.json and .tracelog sample. Covers .trace.json and .tracelog. The tree shows the event count, duration, process, thread and category counts, phase types and display unit, the processes with their named threads, a histogram of phases and the top categories. Judgement: B4: the trace is summarised, but no event is listed or drawn.
What Poka does not read
- Events are not listed and the timeline is not drawn
- Event arguments are not shown
- Flow and async event pairs are not linked
- Caps of 50 processes and categories; files over 256 MiB are cut without a flag
Libraries
Libraries Poka uses or has assessed for this format, with the status, licence and language the registry records.
- serde_json (used; MIT OR Apache-2.0; Rust)
- Perfetto (trace processor) (candidate; Apache-2.0; C++; https://github.com/google/perfetto) — Analyses Chrome JSON traces through its SQL interface; JSON support in older source snapshots was described as rough. Heavyweight for a previewer.
Sources
- parsers/poka-trace-event/src/main.rs
- parsers/poka-trace-event/plugin.json