Diagnosing hooks

Diagnosing Hook Configuration

Goal: reduce any hook problem to a single concrete fix.

Note on trust: plugin hooks execute regardless of the marketplace they came from — third-party plugin hooks run just like built-in ones. Any "diagnostic-only until trusted" wording you may see for marketplace hooks is stale; a plugin's detail view marks each hook as runnable, and that is now true for all hooks.

1. Configuration sources and merging

• Configuration-file hooks: the top-level hooks key in ~/.zcode/cli/config.json (or the workspace <repo>/.zcode/config.json / zcode.json), shaped as { enabled?, timeoutMs?, maxOutputBytes?, events: { <Event>: [ { matcher?, hooks: [...] } ] } }. These are disabled by default — configuration-file hooks must set hooks.enabled: true to run.
• Plugin hooks: each plugin's hooks/hooks.json (or its manifest hooks field). Plugin matchers are appended after configuration matchers. When any plugin contributes a hook, the hook runner is enabled automatically.
• Non-plugin (user or workspace) configuration hooks have no trust gate; with enabled: true they run unconditionally.

2. hooks.json schema

{ "hooks": { "<Event>": [ { "matcher": "...", "hooks": [ { "type": "command"|"process", ... } ] } ] } }

(A plugin file uses the outer hooks wrapper; the configuration file uses hooks.events.<Event>. The inner array is the same.)

• Event names (exactly seven): SessionStart, UserPromptSubmit, PreToolUse, PermissionRequest, PostToolUse, PostToolUseFailure, Stop. Any other name is an unsupported event. (Events such as Notification, SubagentStop, and PreCompact are not supported.)
• The matcher is a case-sensitive regular expression, tested against the event's match value:
  • SessionStart → one of startup, resume, clear, compact
  • Tool events (PreToolUse, PostToolUse, PermissionRequest, PostToolUseFailure) → the tool name (Bash, Read, Write, Edit, Agent, …), with aliases Task ↔ Agent and Write/Edit ← ApplyPatch
  • UserPromptSubmit → the prompt text; Stop → the response preview
  • An omitted matcher matches everything; an invalid regular expression never matches (silently)
• type: "command": command (a shell string); optional shell, timeout (in seconds), timeoutMs (in milliseconds, takes precedence), and statusMessage. Note that async currently has no runtime effect.
• type: "process": command (an executable) plus args[] (an argument vector run without a shell, the most portable choice), timeoutMs (in milliseconds), and statusMessage.
• Timeout resolution: timeoutMs → timeout × 1000 → the configuration's timeoutMs → a default of 60000 ms.
• Template variables (expanded in the command and each argument, and also injected as environment variables): ${CLAUDE_PROJECT_DIR} / ${ZCODE_PROJECT_DIR}, ${CLAUDE_SESSION_ID}; and, for plugin hooks only, ${CLAUDE_PLUGIN_ROOT} / ${ZCODE_PLUGIN_ROOT} and the plugin data directory. Note that a skill-directory variable is not valid in a hook and raises an error.
• Hook output: standard output is parsed as JSON (a strict schema — any extra key fails validation), or you may use exit codes: 0 passes, 2 blocks (a deny for PreToolUse/PermissionRequest), and any other non-zero raises an error. additionalContext is injected into the conversation; PreToolUse may return a permission decision of allow/ask/deny; Stop may request continuation (up to three times).

3. How to inspect hooks

• In the client: Settings → Plugin Management → open a plugin's detail view to see the hooks it registers and whether each is runnable.
• As an agent: read the hooks/hooks.json (or the manifest hooks field) for a plugin, and the hooks block of ~/.zcode/cli/config.json / the workspace config for configuration hooks.
• Execution (fired, timed out, blocked) is recorded in the ZCode log, with the hook's source, matcher, outcome, duration, and a preview of its error stream — enough to distinguish a timeout from a failure from a block.

4. Common pitfalls (symptom → cause → fix)

1. Configuration-file hooks do not run — you added hooks.events.* but nothing fires. They are disabled by default and are enabled automatically only when a plugin hook is present. → Set "hooks": { "enabled": true, ... } in the configuration.
2. Wrong event name — the hook never triggers. → Use exactly one of the seven supported events.
3. Matcher does not match (tool name, case, or regex) — it is registered but never fires for the tool you expect. The matcher is a case-sensitive regular expression; "bash" will not match Bash, and an invalid expression never matches. → Use the exact tool name or a correct expression (for example "Edit|Write"), or omit the matcher to match all. Remember the aliases Task → Agent and Write/Edit → ApplyPatch.
4. Script is not executable — permission denied, with a failed outcome. The script was installed without the executable bit. → Run chmod +x on it, or invoke it through an interpreter, e.g. {"type":"command","command":"bash \"${CLAUDE_PLUGIN_ROOT}/hooks/x.sh\""}, so the executable bit is irrelevant.
5. Template variable not expanded — a literal ${...} or an empty path. Only recognized variables are expanded; a skill-directory variable raises an error inside a hook, and ${CLAUDE_PLUGIN_ROOT} is available only for plugin hooks. → Use only supported variables, and ${CLAUDE_PLUGIN_ROOT} for plugin-relative paths.
6. Timeout unit mistaken — the hook is killed with a timed-out outcome. command's timeout is in seconds; process's timeoutMs is in milliseconds. timeout: 500 means 500 seconds; timeoutMs: 5 means 5 milliseconds. → Use "timeout": <seconds> for a command hook and "timeoutMs": <milliseconds> for a process hook.
7. Command and process fields mixed — the hook is dropped. A process hook accepts only command, args, and timeoutMs; a command hook accepts command, shell, timeout, and timeoutMs. → Match the fields to the type.
8. JSON output fails validation — the hook ran but its effect was discarded and the run marked failed. The output was not valid JSON, contained an extra key (the schema is strict), or its event-specific output named the wrong event. → Emit only the recognized keys with the correct event name, or emit nothing (empty output is fine) and rely on exit codes.
9. Assuming async runs in the background — you set async: true but the session still waits. The async field has no runtime effect and hooks always run inline. → Do not rely on async; for background work, have the script daemonize itself.
10. Cross-platform failure — it works on one operating system but not another. A command hook runs through a shell, so POSIX syntax fails on Windows. → Prefer a process hook (an argument vector, no shell), or ship a polyglot wrapper script and keep hook scripts extensionless.
11. A hook blocks the session unexpectedly — a tool is denied or the run halts. The hook returned a block, exited with code 2, or returned a deny decision. → Inspect the block's reason in the log; fix the script's exit code — return 0 to pass and reserve 2 for a deliberate block.
12. Believing third-party hooks are "diagnostic only" — a third-party plugin hook did not run and you suspect a trust gate. That is not the cause: all plugin hooks are runnable. → Diagnose via pitfalls 2, 3, 4, and 8.

5. Localization workflow (in order)

1. Is a runner active? Confirm that either hooks.enabled: true is set in the configuration or at least one plugin contributes a hook; otherwise no runner exists and every hook is skipped.
2. Enumerate what is registered. In Settings → Plugin Management, open the plugin's detail view and confirm the hook you expect is present and runnable, and that its plugin is enabled. For configuration hooks, read the hooks block directly.
3. Event name and matcher. Check against the seven events; confirm the match value and the case-sensitive expression; test by omitting the matcher (which matches everything).
4. Executable and interpreter. Confirm the script has its executable bit, or invoke it explicitly via bash/node.
5. Run it by hand. Feed a sample hook input to the script and inspect the exit code and output — 0 plus valid JSON is healthy, 2 is a deliberate block, any other non-zero is a failure.
6. Observe live. Trigger the event and read the hook run records in the log (outcome, duration, error-stream preview) to distinguish a timeout from a failure from a block.