Claude Code hooks development guide covering all 10 hook events lifecycle, PostToolUse visibility patterns, PreToolUse guards, Stop hook schema, and debugging. Use when creating hooks, troubleshooting hook output, understanding hook lifecycle, or when user mentions decision block, hook JSON output, stop hook, or Claude Code hooks.
/plugin marketplace add terrylica/cc-skills/plugin install itp-hooks@cc-skillsThis skill inherits all available tools. When active, it can use any tool Claude has access to.
references/debugging-guide.mdreferences/evolution-log.mdreferences/hook-templates.mdreferences/lifecycle-reference.mdreferences/visibility-patterns.mdGuide for developing Claude Code hooks with proper output visibility patterns.
decision: block patternCritical insight: PostToolUse hook stdout is only visible to Claude when JSON contains "decision": "block".
| Output Format | Claude Visibility |
|---|---|
| Plain text | Not visible |
JSON without decision: block | Not visible |
JSON with decision: block | Visible |
Exit code behavior:
| Exit Code | stdout Behavior | Claude Visibility |
|---|---|---|
| 0 | JSON parsed, shown in verbose mode only | Only if "decision": "block" |
| 2 | Ignored, uses stderr instead | stderr shown to Claude |
| Other | stderr shown in verbose mode | Not shown to Claude |
/usr/bin/env bash << 'SKILL_SCRIPT_EOF'
#!/usr/bin/env bash
set -euo pipefail
# Read hook payload from stdin
PAYLOAD=$(cat)
FILE_PATH=$(echo "$PAYLOAD" | jq -r '.tool_input.file_path // empty')
[[ -z "$FILE_PATH" ]] && exit 0
# Your condition here
if [[ condition_met ]]; then
jq -n \
--arg reason "[HOOK] Your message to Claude" \
'{decision: "block", reason: $reason}'
fi
exit 0
SKILL_SCRIPT_EOF
Key points:
jq -n to generate valid JSON"decision": "block" for visibility1. [pending] Create hook script with shebang and set -euo pipefail
2. [pending] Parse PAYLOAD from stdin with jq
3. [pending] Add condition check for when to trigger
4. [pending] Output JSON with decision:block pattern
5. [pending] Register hook in hooks.json with matcher
6. [pending] Test by editing a matching file
7. [pending] Verify Claude sees the message in system-reminder
1. [pending] Verify hook executes (add debug log to /tmp)
2. [pending] Check JSON format is valid (pipe to jq .)
3. [pending] Confirm decision:block is present in output
4. [pending] Verify exit code is 0
5. [pending] Check hooks.json matcher pattern
6. [pending] Restart Claude Code session
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