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systematic-debugging

Find the root cause before proposing any fix. Use when something fails, throws, hangs, flakes, or behaves unexpectedly, including failing tests and CI. Auto-activates for bug reports.

src/skills/builtin/systematic-debugging/SKILL.md

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Nov 5, 2026
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# Debug systematically

A fix without a confirmed cause is a guess, and guesses cost more than they save.
Work the four phases in order; do not propose code before Phase 3 confirms a cause.

## Phase 1 — Reproduce and read

- Read the whole error: message, stack, exit code, the lines around it. The
  answer is often already there.
- Reproduce on purpose. Run the failing command, test, or scenario yourself with
  `run_command`. If it cannot be reproduced, gather more evidence instead of guessing.
- Note what changed: `git_log` and `git_diff` for the touched area, new
  dependencies, config, environment (CI vs local, OS, shell, terminal, load).
- For multi-layer systems, add cheap instrumentation at each boundary and run