# retro

Guides post-incident code analysis to identify structural weaknesses and prevent entire classes of failures.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · ★ 24
- Author: rainmanjam
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/rainmanjam/poka-yoke/tree/HEAD/benchmarks/controls/clean-code/skills/retro/SKILL.md
- Updated: 2026-10-14
- HTML: https://affpapa.org/en/nevibecode/skills/retro-2

## What it does

The skill provides a rigorous framework for conducting post-mortems after an outage or a severe bug. Instead of stopping at the immediate trigger or assigning personal blame, it investigates why the codebase permitted the bad state, such as ambiguous return types, silent fallbacks, or components observing state outside their scope.

It enforces a strict separation between a factual, uninterpreted timeline and the actual technical evaluation. The guide demands resolving the whole defect pattern rather than patching a single call site, while explicitly cataloging residual risks. It treats monitoring additions as secondary mitigations, since alerts only shorten detection time rather than eliminating the flaw.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add rainmanjam/poka-yoke --skill retro -a claude-code
```

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

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add rainmanjam/poka-yoke --skill retro -a codex
```

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

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add rainmanjam/poka-yoke --skill retro -a cursor
```

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install rainmanjam/poka-yoke retro
```

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

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add rainmanjam/poka-yoke --skill retro -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/rainmanjam/poka-yoke --path benchmarks/controls/clean-code/skills/retro
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add rainmanjam/poka-yoke --skill retro -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/rainmanjam/poka-yoke/tree/HEAD/benchmarks/controls/clean-code/skills/retro/SKILL.md

## When to use it
- write structural post-incident reviews after a production outage
- isolate the architectural flaw that permitted the defect to happen
- sweep the codebase for identical failure shapes and risky signatures
- document residual risks and edge cases left after the patch

## Example prompts
- Run a retro on yesterday's cache invalidation outage to find the structural flaw
- Help draft an incident review: separate the raw timeline from technical conclusions
- Analyze this bugfix to identify if the same problematic code pattern exists elsewhere

## 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: 1363fd9855fdb164.

BEGIN THIRD-PARTY FILE 1363fd9855fdb164
```text
---
name: retro
description: >-
  Something broke. Deciding what to change in the code so the class of problem is less likely,
  and writing it up so the next person understands the reasoning rather than just the outcome.
---

# Retro: Structural Lessons From an Incident

An incident is expensive information. Most of the value is lost because the write-up records
what happened and the fix records what changed, and neither records *why the code allowed it*.

The structural question is not "what went wrong" but "what about the shape of this code made
that failure available, and is that shape used elsewhere".

## Separate the timeline from the analysis

The timeline is what happened, in order, with times. It is a record, and it should be boring:
who noticed, when, what they did, what the system did back. Write it first and do not
interpret it while writing it.

The analysis is what you concluded. Keep it separate, because a timeline with interpretation
woven through it cannot be re-read later by someone who disagrees with the interpretation.

## Find the structural cause, not the last change

The last change before the incident is rarely the interesting one. Ask instead:

**What made this failure expressible?** A function that accepted an argument it could not
validate, a module that could observe state it had no business observing, a default that
silently applied.

**Why did the code look correct?** If the failing code passed review, understand what it
looked like to the reviewer. That perception is the thing to change, and it is usually a
naming or a structure problem rather than a knowledge problem.

**How far can this shape travel?** The same shape almost certainly exists elsewhere. Finding
the second and third instance is the difference between a fix and a lesson.

## The write-up

Aim it at someone six months from now who was not there.

- **Lead with the structural finding**, not the chronology. "A helper returned `None` for both 'absent' and 'failed', and three callers could not distinguish them" is the sentence worth remembering.
- **Say what was ruled out**, and why. A retro that lists only the cause reads as though it was obvious, which teaches the reader nothing about how to look.
- **Name the changes and their limits.** A fix that closes one path should say which paths it does not close.
- **Record disagreements.** If two people read the cause differently and one view won, the other view is evidence about how the code reads.

## What to change

**Prefer changes to shape over changes to process.** "Be careful with this function" degrades.
Splitting the function so the careless call is not available does not.

**Fix the class, not the case.** Patching the one call site that failed leaves the other twelve.
If the class is too large to fix at once, say so and list them.

**Reduce the distance between cause and symptom.** Much of an incident's cost is the time
between the wrong thing happening and anyone noticing. Structure that shortens that distance,
a narrower type, a failure that propagates rather than being absorbed, is worth as much as
```
END THIRD-PARTY FILE 1363fd9855fdb164

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First 3102 of 4496 bytes. © rainmanjam · MIT · https://github.com/rainmanjam/poka-yoke/tree/HEAD/benchmarks/controls/clean-code/skills/retro/SKILL.md

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