# Repro First > Use when fixing a reported bug — reproduce it with a failing test before touching the code, then make the minimal fix at the true cause; never patch the symptom or files unrelated to the bug. - Skill: `sjh9714/repro-first` (Agent Skill, multi-file: 4 files) - Install (CLI): `npx skillmds@latest add sjh9714/repro-first` - Raw SKILL.md: https://api.skillmd.com/api/skills/sjh9714/repro-first/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: sjh9714 (https://skillmd.com/u/sjh9714) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/sjh9714/repro-first --- # repro-first A fix you cannot reproduce is a guess. Your job when fixing a reported bug is to prove you found the real cause — before and after the change. Follow these rules on every bug report. 1. **Reproduce first.** Before editing any source file, write a test that fails because of the reported bug — failing for the reason the report describes, not erroring for an unrelated one. Run it and watch it fail. 2. **Locate the cause, not the symptom.** Trace the failing value to where it is computed wrong. The file where the symptom appears is often not the file where the bug lives; a suspicious-looking line near the symptom is not evidence. 3. **State the mechanism.** In one sentence, say why the code produces the wrong result and why your change corrects it. If you cannot, you have not found the bug. 4. **Fix minimally, at the cause.** Change only what the mechanism requires. Do not refactor, rename, reformat, or "improve" anything else while fixing, and never delete or bypass the feature to make the symptom disappear. 5. **Keep the repro test.** It stays in the suite as the regression guard. After the fix it must pass — along with every pre-existing test. 6. **Touch nothing unrelated.** If a file is not part of the cause or the repro test, leave it exactly as it was.