janestreet/magic-trace

Health v2 · maintenance only

Adoption not part of the score

6249 stars · 209 forks observed · 2026-08-28

What it is AI-extracted, prompt v1, taxonomy v1, 2026-08-29, confidence not recorded

magic-trace is an OCaml CLI tool that uses Intel Processor Trace to capture high-resolution traces of every function call a process makes, with ~40ns resolution and low overhead. It renders an interactive timeline of call stacks leading up to a chosen point in time, useful for diagnosing latency spikes and pre-crash behavior.

Use cases

• find why some production requests are slow while others are fast
• trace every function call of a running process without code changes
• see what an application did before it crashed
• snapshot a trace when a specific function is called
• profile a program with low overhead like perf but with full control flow

When to choose

• you need high-resolution function-level tracing on Linux with Intel PT hardware
• you want to capture a trace of the moments before a crash or slow request
• you can't modify the application to add instrumentation

When to avoid

• you're on non-x86 hardware or lack Intel Processor Trace support
• you need long-duration traces rather than ~10ms ring-buffer snapshots
• you need a sampling-based statistical profiler across long time windows

Facets

cli-tool · maturity active

tracing monitoring developer-tools cli developer-tools performance cli intel-processor-trace profiling call-stack-timeline perf x86 perfetto command-line linux

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