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phx:learn-from-fix

This Claude Code skill documents lessons learned after fixing bugs or receiving corrections in Elixir Phoenix development. Use it when you encounter and resolve issues related to Ecto queries, LiveView patterns, Oban jobs, or common mistakes. The skill systematically captures root causes as reusable rules in project documentation or auto-memory files, preventing recurrence of the same errors across future work.

View source Repository: claude-elixir-phoenix

Install in Claude Code

Copy

git clone --depth 1 https://github.com/oliver-kriska/claude-elixir-phoenix /tmp/phx-learn-from-fix && cp -r /tmp/phx-learn-from-fix/plugins/elixir-phoenix/skills/learn-from-fix ~/.claude/skills/phx-learn-from-fix

Then start a new Claude Code session; the skill loads automatically.

Definition

SKILL.md

# Learn From Fix

After fixing a bug or receiving a correction, capture the lesson
to prevent future mistakes.

## Usage

```
/phx:learn-from-fix Fixed N+1 query in user listing - was missing preload
/phx:learn-from-fix String vs atom key mismatch in params handling
/phx:learn-from-fix LiveView assign_async needs render_async in tests
```

## Workflow

### Step 1: Identify the Pattern

Look at recent conversation context. Ask yourself:

- What was the root cause? (not the symptom)
- Is this a common mistake others might make?
- Can it be prevented with a simple rule?

### Step 2: Check Existing Knowledge

Check if already documented:

- Grep project CLAUDE.md for the pattern keyword
- Check auto-memory files for similar lessons
- Read `${CLAUDE_SKILL_DIR}/references/common-mistakes.md` (READ-ONLY plugin
  reference — do NOT edit this file)

If already documented, tell the user and stop.

### Step 3: Decide Where to Save

**CRITICAL: NEVER edit plugin files.** Files under
`~/.claude/plugins/` are cached and get overwritten on updates.
Always write to project or memory locations.

| Scope | Write to | Example |
|-------|----------|---------|
| This project only | Project CLAUDE.md | "Never use raw SQL in this app" |
| All Elixir projects | Auto-memory MEMORY.md | "jsonb always uses string keys" |
| Detailed fix with context | `.claude/solutions/` via `/phx:compound` | Complex debugging story |

### Step 4: Write the Lesson

**For project CLAUDE.md** — append a concise rule:

```markdown
### [Category] Iron Laws (continued)

N. **[SHORT RULE NAME]** — Do NOT [bad pattern]. Instead [good pattern]
```

**For auto-memory** — append to
`~/.claude/projects/{project-hash}/memory/MEMORY.md`:

```markdown
### Lesson: [Title]
- **Pattern**: Do NOT [bad] — instead [good]
- **Why**: [root cause explanation]
```

### Step 5: Consider Broader Updates

If the lesson is significant enough to be an Iron Law:

- Suggest adding to project CLAUDE.md Iron Laws section
- If it's universal (applies to all Elixir projects), suggest
  updating the plugin itself (the user can PR it)

## Output

After capturing, confirm:

```text
Lesson captured in [location]

Pattern: Do NOT [bad pattern] — instead [good pattern]
Category: [Ecto/LiveView/OTP/Testing/etc]
```

## Iron Laws

1. **NEVER edit plugin files** — files under `~/.claude/plugins/` are cached and overwritten on updates
2. **DO NOT duplicate existing lessons** — always check CLAUDE.md and memory before writing
3. **Capture the root cause, not the symptom** — "missing preload" not "query was slow"

## References (READ-ONLY — do NOT edit)

- `${CLAUDE_SKILL_DIR}/references/common-mistakes.md` — Common Elixir mistakes
  reference. Consult when checking for duplicates. Ships with
  the plugin — NEVER modify.