Configure Hooks

Configure Hooks

Set up event-driven hooks in .claude/settings.json. Hooks execute external commands; their exit codes mechanically affect agent behavior in ways that CLAUDE.md instructions cannot.

This skill is paired with validate-hooks.py. After writing the config, the skill runs the validator to catch any fictional event names — earlier versions of this plugin propagated four hook events that don't actually exist in Claude Code (PostToolUseFailure, SubagentStart, Setup, InstructionsLoaded).

Source

• Hook event list and semantics: Claude Code Hooks Reference (verified April 2026)
• Exit code semantics, matcher behavior, parallel execution: same source

Hook event semantics (verified April 2026)

Exit 0  →  Proceed (stdout added to context for some events; parsed as JSON if applicable)
Exit 2  →  Block the action; stderr becomes feedback to Claude
Other   →  Logged as non-blocking error; stderr shown to Claude

Note: Exit 1 is treated as non-blocking error — not as "failure" in the Unix sense. If you want to block, use exit 2.

Documented hook events

These are the only events Claude Code fires (April 2026). Use any other name and the hook will silently never fire.

Matcher behavior (often misunderstood): the matcher field uses exact string match when no special characters are present. Regex matching kicks in only when the value contains regex metacharacters like |, ^, $, .*. So "Bash" matches the Bash tool exactly; "Edit|Write" matches either; "^Notebook" is regex.

Standard hook patterns

Quality gate on TaskCompleted (experimental — Agent Teams only)

Runs typecheck + tests when a teammate marks a task complete. Blocks completion if either fails. Requires CLAUDE_CODE_EXPERIMENTAL_AGENT_TEAMS=1.

{
  "hooks": {
    "TaskCompleted": [{
      "hooks": [{
        "type": "command",
        "command": "cd \"$CLAUDE_PROJECT_DIR\" && npm run typecheck 2>&1 | tail -20; TC=$?; npm test 2>&1 | tail -30; TEST=$?; if [ $TC -ne 0 ] || [ $TEST -ne 0 ]; then echo 'BLOCKED: typecheck or tests failed' >&2; exit 2; fi",
        "timeout": 120
      }]
    }]
  }
}

Typecheck on edit (PostToolUse)

Warns (does not block — PostToolUse can't block) when an edit introduces TypeScript errors:

{
  "hooks": {
    "PostToolUse": [{
      "matcher": "Write|Edit",
      "hooks": [{
        "type": "command",
        "command": "cd \"$CLAUDE_PROJECT_DIR\" && npm run typecheck 2>&1 | tail -5; if [ $? -ne 0 ]; then echo 'Warning: TypeScript errors after edit' >&2; fi; exit 0",
        "timeout": 30
      }]
    }]
  }
}

Context restoration after compaction (SessionStart)

{
  "hooks": {
    "SessionStart": [{
      "matcher": "compact",
      "hooks": [{
        "type": "command",
        "command": "echo 'Reminder: current sprint focus is [SPRINT_GOAL]. Use the project agents for implementation.'"
      }]
    }]
  }
}

Secret scan before write (PreToolUse)

{
  "hooks": {
    "PreToolUse": [{
      "matcher": "Write|Edit",
      "hooks": [{
        "type": "command",
        "command": "echo \"$TOOL_INPUT_CONTENT\" | grep -iE '(api[_-]?key|secret|password|token)\\s*[=:]\\s*[\"''']?[A-Za-z0-9+/]{20,}' && echo 'BLOCKED: possible secret in content' >&2 && exit 2 || exit 0",
        "timeout": 5
      }]
    }]
  }
}

Stop hook with guard (avoid infinite loop)

If you want a Stop hook that exits 2 sometimes (preventing the agent from stopping), use a sentinel file or counter to ensure the hook eventually allows the stop:

{
  "hooks": {
    "Stop": [{
      "hooks": [{
        "type": "command",
        "command": "COUNT=$(cat /tmp/stop-count 2>/dev/null || echo 0); if [ $COUNT -ge 3 ]; then rm -f /tmp/stop-count; exit 0; fi; echo $((COUNT+1)) > /tmp/stop-count; echo 'Continuing — N more cycles allowed' >&2; exit 2",
        "timeout": 5
      }]
    }]
  }
}

Without the guard, an unconditional exit 2 on Stop creates an infinite loop. The validator script flags this pattern.

Workflow

Step 1: Determine target

Find .claude/settings.json. Read existing if present (so the merge preserves other config). Create otherwise.

Step 2: Select hook patterns

Present the menu. If --hooks specifies a subset, use those. Standard options:

Step 3: Customize commands per stack

• npm run typecheck → pnpm typecheck, bun typecheck, mypy app/
• npm test → pnpm test, pytest, cargo test
• Adjust timeouts based on test-suite duration

Step 4: Merge into settings.json

Read existing .claude/settings.json (if any), merge in the new hook entries, preserve other config. Write the result.

Step 5: Run the validator

python3 ${plugin_root}/scripts/validate-hooks.py <path-to-settings.json>

If the validator finds fictional events, broken handler shapes, or unguarded Stop-exit-2 patterns, surface them before declaring done. The validator is the safety net; do not skip this step.

Step 6: Report

Tell the user:

• Which hooks were added
• What each will do (block / warn / inform)
• Important caveats (Agent Teams experimental flag if TaskCompleted was used; loop risk for unguarded Stop hooks)

What this skill does NOT do

• Does not invent hook events. Anything not in the documented event list will be rejected by validate-hooks.py.
• Does not test that the hooks fire correctly — restart Claude Code and exercise the relevant tool to verify.
• Does not configure Agent Teams (experimental — see agentic-operations for the env var to enable).
• Does not handle hook removal — edit settings.json directly.

Reference

• references/hook-patterns.md — Additional patterns (auto-format, advanced secret-scan, stop-guard variations)