# debug-hooks

Systematic debugging guide for Claude Code hooks when events fail to fire, run twice, or swallow runtime errors.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 499 installs · ★ 3946
- Author: parcadei
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/parcadei/Continuous-Claude-v3/tree/HEAD/.claude/skills/debug-hooks/SKILL.md
- Updated: 2026-01-26
- HTML: https://affpapa.org/en/nevibecode/skills/debug-hooks

## What it does

The skill provides an inspection sequence for `SessionEnd` and `PostToolUse` hooks. It directs the agent to check outputs before modifying any code. Claude Code inspects the `.claude/cache/` directory, checks debug logs, and inspects `settings.json` to find missing registrations or duplicate hooks.

To pinpoint failure points, the workflow pipes mock JSON payloads into shell wrappers. Silent failures often occur in detached spawns configured with `stdio: 'ignore'`. When that happens, the skill routes stdout and stderr into a temporary log file.

TypeScript source edits will not alter behavior immediately. The shell wrapper executes the bundled `.mjs` file in `dist/`. You must run an `esbuild` command after code modifications. The skill requires `Bash`, `Read`, and `Grep` tools.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add parcadei/Continuous-Claude-v3 --skill debug-hooks -a claude-code
```

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

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add parcadei/Continuous-Claude-v3 --skill debug-hooks -a codex
```

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

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add parcadei/Continuous-Claude-v3 --skill debug-hooks -a cursor
```

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

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install parcadei/Continuous-Claude-v3 debug-hooks
```

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

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add parcadei/Continuous-Claude-v3 --skill debug-hooks -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/parcadei/Continuous-Claude-v3 --path .claude/skills/debug-hooks
```

### Windsurf (Devin Desktop)

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

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add parcadei/Continuous-Claude-v3 --skill debug-hooks -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/parcadei/Continuous-Claude-v3/tree/HEAD/.claude/skills/debug-hooks/SKILL.md

## When to use it
- identify why SessionEnd or PostToolUse hooks fail to trigger
- test hook scripts manually with mock JSON payloads
- capture silent failures hidden by detached spawn calls
- fix duplicate hook runs caused by conflicting settings

## Example prompts
- My PostToolUse hook isn't firing, help me debug it
- Check why the SessionEnd cleanup script produces no logs
- Verify my hook registration in .claude/settings.json

## 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: 560bc3cdaf0dd59f.

BEGIN THIRD-PARTY FILE 560bc3cdaf0dd59f
````text
---
name: debug-hooks
description: Systematic hook debugging workflow. Use when hooks aren't firing, producing wrong output, or behaving unexpectedly.
allowed-tools: [Bash, Read, Grep]
---

# Debug Hooks

Systematic workflow for debugging Claude Code hooks.

## When to Use

- "Hook isn't firing"
- "Hook produces wrong output"
- "SessionEnd not working"
- "PostToolUse hook not triggering"
- "Why didn't my hook run?"

## Workflow

### 1. Check Outputs First (Observe Before Editing)

```bash
# Check project cache
ls -la $CLAUDE_PROJECT_DIR/.claude/cache/

# Check specific outputs
ls -la $CLAUDE_PROJECT_DIR/.claude/cache/learnings/

# Check for debug logs
tail $CLAUDE_PROJECT_DIR/.claude/cache/*.log 2>/dev/null

# Also check global (common mistake: wrong path)
ls -la ~/.claude/cache/ 2>/dev/null
```

### 2. Verify Hook Registration

```bash
# Project settings
cat $CLAUDE_PROJECT_DIR/.claude/settings.json | grep -A 20 '"SessionEnd"\|"PostToolUse"\|"UserPromptSubmit"'

# Global settings (hooks merge from both)
cat ~/.claude/settings.json | grep -A 20 '"SessionEnd"\|"PostToolUse"\|"UserPromptSubmit"'
```

### 3. Check Hook Files Exist

```bash
# Shell wrappers
ls -la $CLAUDE_PROJECT_DIR/.claude/hooks/*.sh

# Compiled bundles (if using TypeScript)
ls -la $CLAUDE_PROJECT_DIR/.claude/hooks/dist/*.mjs
```

### 4. Test Hook Manually

```bash
# SessionEnd hook
echo '{"session_id": "test-123", "reason": "clear", "transcript_path": "/tmp/test"}' | \
  $CLAUDE_PROJECT_DIR/.claude/hooks/session-end-cleanup.sh

# PostToolUse hook (Write tool example)
echo '{"tool_name": "Write", "tool_input": {"file_path": "test.md"}, "session_id": "test-123"}' | \
  $CLAUDE_PROJECT_DIR/.claude/hooks/handoff-index.sh
```

### 5. Check for Silent Failures

If using detached spawn with `stdio: 'ignore'`:

```typescript
// This pattern hides errors!
spawn(cmd, args, { detached: true, stdio: 'ignore' })
```

**Fix:** Add temporary logging:

```typescript
const logFile = fs.openSync('.claude/cache/debug.log', 'a');
spawn(cmd, args, {
  detached: true,
  stdio: ['ignore', logFile, logFile]  // capture stdout/stderr
});
```

### 6. Rebuild After Edits

If you edited TypeScript source, you MUST rebuild:

```bash
cd $CLAUDE_PROJECT_DIR/.claude/hooks
npx esbuild src/session-end-cleanup.ts \
  --bundle --platform=node --format=esm \
  --outfile=dist/session-end-cleanup.mjs
```

Source edits alone don't take effect - the shell wrapper runs the bundled `.mjs`.

## Common Issues

| Symptom | Likely Cause | Fix |
|---------|--------------|-----|
| Hook never runs | Not registered in settings.json | Add to correct event in settings |
| Hook runs but no output | Detached spawn hiding errors | Add logging, check manually |
| Wrong session ID | Using "most recent" query | Pass ID explicitly |
| Works locally, not in CI | Missing dependencies | Check npx/node availability |
| Runs twice | Registered in both global + project | Remove duplicate |

## Debug Checklist

- [ ] Outputs exist? (`ls -la .claude/cache/`)
````
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