Runtimes Matrix

Monitor's error tracking is SDK-free: it parses what a runtime already prints. What each runtime gets, at a glance:

Runtime	Crash parsing (monitor run -- / stacktrace parse)	Live hot lines (monitor hot)	Exit-time profile (monitor run --profile)	Source maps
Node	Yes — uncaught exceptions and caught-and-printed errors on stderr/stdout	Yes — started with --inspect, or launched under monitor run --inspect	Yes — V8 .cpuprofile written at exit	Crash stacks: runtime-level --enable-source-maps (appended to NODE_OPTIONS at launch). Hot lines: monitor's own Source Map v3 resolver (mapping: exact/ambiguous)
Deno	Yes	Yes — Deno honors NODE_OPTIONS=--inspect the same way Node does	Not yet — Deno has no env-injectable --cpu-prof; use --inspect + monitor hot <service> for live profiling instead	Same as Node
Bun	Yes	No live lines — Bun's inspector speaks JSC, not V8's CDP; hot lines only at exit	Yes — via BUN_OPTIONS' --cpu-prof	Same as Node
Python	Yes — tracebacks, including raise ... from cause chains	Errors only — Python hot lines need launch-time probes (a later epic)	No	n/a
Ruby	Yes — exceptions with backtraces, including rescue-printed backtraces without a message	Errors only — same as Python	No	n/a
Go	Yes — panics, plus zap, pkg/errors-style and fmt.Errorf("%w") wrapped-error chains	Exact lines need net/http/pprof (--pprof-addr); without it, macOS sample is function-level only	No — use net/http/pprof with monitor hot/monitor profile	n/a

All six runtimes' crashes group into the same issue store with the same culprit file:line rule — see Your First Issue and Local Issues.

Crash parsing details

monitor run -- <cmd> scans stderr by default (--scan stdout or --scan both for loggers that print to stdout — some zap setups, pino, many Rails loggers). The detector understands, per runtime:

• V8 family (Node/Deno/Bun): uncaught exceptions, Error.cause chains printed as [cause], console.error(err.stack), and typescript-logging output.
• Python: tracebacks with __cause__/__context__ chaining ("The above exception was the direct cause of..."), logging output.
• Ruby: raised exceptions with backtraces, warn e.backtrace.
• Go: panics, plus zap and pkg/errors/fmt.Errorf("%w") chains printed in %+v form.

Parsed text is scrubbed before it is persisted (provider-shaped secrets, emails, Luhn card numbers, URL credentials, and the exact values of secret-named environment variables — --redact-env adds more names). Lines are never dropped for the child's sake: the copy to the terminal comes first, and a full detector buffer drops and counts rather than applying back-pressure.

One buffering caveat, printed by run -- itself when it applies: a scanned stream becomes a pipe, which changes some runtimes' stdio buffering. Python is handled (PYTHONUNBUFFERED=1 is set when --scan includes stdout); Ruby has no equivalent, so a scanned Ruby stdout may arrive in the terminal in blocks until the process exits. Scanning stderr (the default) avoids this.

Hot lines and profiles details

• Live hot lines need a sampler that reports positions, which for Node/Deno means the V8 inspector (CDP positionTicks). monitor run --inspect opens one at launch and registers it in the launch registry for monitor hot <service>; the inspector's ws:// URL is never printed — only the port. For details see Hot Lines.
• Exit-time profiles (monitor run --profile) work for Node and Bun via the runtime's own --cpu-prof flags, flushed by an exit shim that even a bare Ctrl-C reaches — unless the application installs its own SIGINT/SIGTERM handler, in which case monitor leaves it completely alone.
• Go exactness depends on the profile source: a pprof proto (net/http/pprof) is line-exact and inlining-aware; macOS sample (the fallback when no pprof endpoint exists) is function-level only.
• monitor profile is runtime-aware independently of hot: CDP for Node/Deno processes with --inspect, ownership-verified net/http/pprof for Go heap/cpu/goroutine, macOS sample as the final fallback.

Source maps

Two different mechanisms, both on by default:

• Crash stacks are symbolicated by the runtime itself: monitor run -- appends --enable-source-maps to NODE_OPTIONS (creating it if unset, always appending, never overwriting) so Node/Deno/Bun print original .ts/source positions in their own stack traces. --no-source-maps leaves NODE_OPTIONS completely alone.
• Hot lines from a .cpuprofile or CDP capture are resolved by monitor's own dependency-free Source Map v3 decoder: generated positions map back to original lines with a per-line confidence of exact or ambiguous (a minified bundle that collapses many statements onto one generated line is ambiguous, never silently exact), and a map older than the file it maps is flagged stale with a warning instead of being trusted.

The examples/polyglot/ directory ships a workload per runtime (js/ for Node/Bun/Deno, python/, ruby/, and several Go programs); WORKLOAD_SECONDS=3 shortens any of them.