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ummshunummshun/claude-code-skills/skills/hook-latency-wrap/SKILL.md

hook-latency-wrap

Skill0 starsChanged 46 days agoMITView on GitHub

Use when measuring the duration and failure rate of any Claude Code hook, such as PostToolUse, Stop, or UserPromptSubmit, with a transparent Bash wrapper based on EPOCHREALTIME.

1 other project uses a version of this.

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  • Other versions1 project uses a version of this.

    Word for word · 0

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    Wrote their own version · 1

    1. bokuwalily/claude-code-skills★ 0same name

    How matches are found. Word for word: the exact same text. Edited: shares passages with this file (“99% same” means 99% of its five-word phrases also appear here; 10% or more counts). Their own version: similar meaning, or, weakest, the same name. We can’t tell which project had it first. Projects are counted among the 200 most-starred candidates, and mentions are links to the repository we found, up to 50 per site, so both counts are a floor.

  • In this repository2 other files it gives its agents.

The file

We split this skill into the rules it gives an agent

2 rules. About 0 are common, 1 is distinctive, and 1 is very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈1

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 1

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Create a wrapper command that accepts the real hook path as its first argument, preserves stdin, and records $EPOCHREALTIME immediately …

    line 13
  2. Distinctive:

    Keep metrics on a separate file descriptor so hook stdout and stderr do not enter the JSONL log.

    line 23

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Procedure

  1. Create a wrapper command that accepts the real hook path as its first argument, preserves stdin, and records $EPOCHREALTIME immediately before and after invoking the hook.
  2. Append one JSONL record per run with fields such as ts, hook, duration_ms, and exit_code. Store it under $HOME/.claude/logs/ or another configurable log directory.
  3. Replace the target hook's command in settings.json with the wrapper followed by the real hook path. The same wrapper can instrument multiple hooks.
  4. Return the real hook's exit code. If metrics logging itself fails, do not mask or replace the hook result.
  5. Aggregate a bounded time window, such as the last seven days, by hook name and report p50, p95, maximum duration, and failure rate.

Pitfalls

  • $EPOCHREALTIME requires Bash 5 or newer. macOS ships Bash 3.2, so use an installed Bash 5 path in the wrapper shebang.
  • Spawning Python for each timing operation can add enough overhead to distort short hooks.
  • Keep metrics on a separate file descriptor so hook stdout and stderr do not enter the JSONL log.
  • Fire-and-forget hooks finish after the wrapper exits, so wrapper duration does not represent their actual completion time.
  • Measure wrapper overhead separately if millisecond-level precision matters.

Verification

  • Run bash -n <wrapper-path>.
  • Pipe a small JSON object into the wrapper and a harmless test hook.
  • Confirm that stdin reaches the hook unchanged, the wrapper returns the same exit code, and exactly one valid JSONL record is added.
  • Trigger the configured Claude Code hook and confirm the report includes it with plausible timing values.

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