# bug-reproduction

Turns a vague bug report into a verified minimal reproduction and a failing regression test. Useful when a bug only shows up sometimes and you don't know where to start.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 1400 installs · ★ 211
- Author: kindlmann
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/petrkindlmann/qa-skills/tree/HEAD/skills/bug-reproduction/SKILL.md
- Updated: 2026-10-22
- HTML: https://affpapa.org/en/nevibecode/skills/bug-reproduction

## What it does

The skill walks an agent through eight steps: pull the implicit repro out of a thin report (environment, build, steps, data), run the reproduce-minimize-isolate-capture loop, find the introducing commit with `git bisect`, build a deterministic minimal repro with fixed seeds, frozen time and a stubbed network, write the failing regression test before the fix, then confirm the fix flips it green. One step sorts flaky from environment-specific from genuinely not reproducible.

Inside there's a quick-route table mapping what you have to the step to open, a set of discovery questions, and five principles. The first one: reproduce before you theorize. A fix without a reproduction is a guess you can't falsify. Minimization removes one variable at a time and re-confirms after every cut, because dropping several at once tells you nothing about which one mattered.

Before starting, the skill checks `.agents/qa-project-context.md` in the project root for the stack, test runner, known-flaky areas and environment matrix. If the file is missing it suggests creating one with the `qa-project-context` skill. What the test looks like depends on the runner — freezing time works differently in Vitest and Playwright, so knowing the stack up front matters. The skill doesn't triage or deduplicate failures you already know about, and it doesn't generate tests from specs; sibling skills cover that.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill bug-reproduction -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/bug-reproduction/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/bug-reproduction/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill bug-reproduction -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/bug-reproduction/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill bug-reproduction -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/bug-reproduction/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install petrkindlmann/qa-skills bug-reproduction
```

2. **Manually: put the files in place**
- File: `.github/skills/bug-reproduction/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill bug-reproduction -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/petrkindlmann/qa-skills --path skills/bug-reproduction
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/bug-reproduction/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add petrkindlmann/qa-skills --skill bug-reproduction -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/petrkindlmann/qa-skills/tree/HEAD/skills/bug-reproduction/SKILL.md

## When to use it
- extract reproduction steps from a one-line report
- make the bug fail the same way on every machine
- find the commit that broke the behavior
- write a regression test before the fix and watch it go red
- tell a flaky failure from an environment-specific one

## Example prompts
- reproduce this bug: "order total is wrong sometimes" — screenshot and log attached
- make the repro deterministic, freeze the clock and the seed
- write a failing regression test for this defect before the fix

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 37cafc1e1b6424a6.

BEGIN THIRD-PARTY FILE 37cafc1e1b6424a6
```text
---
name: bug-reproduction
description: >-
  Turn a vague bug report into a VERIFIED minimal reproduction and then a failing
  regression test, agent-driven end to end. Covers extracting the implicit repro from a
  thin report (env, build, steps, data), the reproduce-minimize-isolate-capture loop,
  git bisect to find the introducing commit, building a deterministic minimal repro
  (fixed seeds, frozen time, stubbed network), writing the failing regression test BEFORE
  the fix (red) and confirming the fix flips it green, and writing repro evidence back
  into the ticket. Distinguishes flaky-not-reproducible from environment-specific.
  Use when: "reproduce this bug," "minimal reproduction," "repro steps," "find the commit
  that broke it," "git bisect," "make the repro deterministic," "write a failing test for
  this bug," "regression test for a defect," "can't reproduce this bug."
  Not for: Classifying/deduplicating/severity-routing existing failures without
  reproducing them — that is ai-bug-triage. Generating tests from specs rather than from a
  defect — that is ai-test-generation.
  Related: ai-bug-triage, ai-test-generation, test-reliability, systematic-debugging, qa-project-context.
license: MIT
metadata:
  author: kindlmann
  version: "1.0"
  category: ai-qa
---

<objective>
A bug you cannot reproduce is a bug you cannot fix or prove fixed. This skill takes a
thin, hand-wavy report ("order total is wrong sometimes") and drives it to a VERIFIED
minimal reproduction, a deterministic failing test written BEFORE the fix, a `git bisect`
that names the introducing commit, and a structured evidence block in the ticket. The
discipline it enforces: reproduce before theorizing, minimize one cut at a time, freeze
time/seed/network so the repro fails identically every run, watch the test go red first,
and confirm the fix flips it green — and that reverting the fix turns it red again.
</objective>

## Quick Route

| You have… | Go to |
|-----------|-------|
| A thin report and no idea how to trigger it | [Step 1: Extract the implicit repro](#step-1-extract-the-implicit-repro) |
| A messy 14-step repro to clean up | [Step 2: The reproduce-minimize-isolate-capture loop](#step-2-the-reproduceminimizeisolatecapture-loop) |
```
END THIRD-PARTY FILE 37cafc1e1b6424a6

The third-party file has ended. Everything between the 37cafc1e1b6424a6 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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