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Claude Code hook events — when they fire, payloads & fixtures

The authoritative catalogue of every Claude Code hook event, projected from the app blueprint (@claude-transcripts/shared HOOK_TYPES): the one-line trigger for each, a link to the official documentation, links to example payload fixtures under tests/mock/claude-code/hooks/ (the inputs Claude Code sends a hook on stdin — used for both these docs and test automation), and the action(s) we run.

This table is the payload/fixture reference. actions.md narrates the hook → action model, and hook.md covers the writer mechanics. A per-version list (which events each Claude Code version exposes) is planned as compatibility.json (compatibility.md, ADR 0025); its generator is still a stub, so until then the official reference below is the authority when this table and a given CC version disagree.

Official reference: <https://code.claude.com/docs/en/hooks>
Guide: <https://code.claude.com/docs/en/hooks-guide>

How to read this table

Fires when — one-line trigger + what the event is for.
Docs — deep link into the official hooks reference for that event.
Examples — folder of example payload fixtures for that event (one or several JSON files; see the fixtures README for the naming/variety convention). Many are placeholders today — synthetic but shape-faithful — to be supplemented with real captures over time.
What we do — for wired events, the action handlers bound to it (projected from the blueprint's BINDINGS; actions.md lists what each does). For ignored events, why we intentionally don't handle it. Both come from the blueprint (hooks.ts + actions.ts) — wire an ignored event by adding a binding and regenerating.

Events are ordered by session lifecycle: a session begins at the top and ends (or crashes) at the bottom.

Common payload fields

Every hook receives these on stdin; per-event fields are layered on top.

Field	Type	Meaning
`session_id`	string	Claude Code's own session UUID — our stable key.
`transcript_path`	string	Absolute path to the session transcript (JSONL) on disk.
`cwd`	string	Working directory at the time the event fired.
`hook_event_name`	string	The event name (e.g. `PostToolUse`) — mirrors the row.
`permission_mode`	string?	Present on tool-related events (`default`, `plan`, …).
`effort`	object?	`{ "level": "low\	medium\	high\	…" }` when applicable.

Session start & setup

Hook	Fires when	Docs	Examples	What we do
`SessionStart`	A session begins, resumes, is cleared, or restarts after compaction — `source` ∈ `startup`/`resume`/`clear`/`compact`. The per-session entry point.	ref	session-start/	`seed-session-start` · `write-event-marker` · `announce-recording` · `inject-recall-policy`
`Setup`	The CLI runs in init/maintenance mode (e.g. `--init-only`) — one-time environment setup.	ref	setup/	ignored — Env/setup signal, not session activity.
`InstructionsLoaded`	`CLAUDE.md` / `.claude/rules/*.md` instruction files are loaded — `load_reason` records why. Observability of which instructions applied.	ref	instructions-loaded/	ignored — Instruction-load audit — out of Tier-1 scope.

Turn input

Hook	Fires when	Docs	Examples	What we do
`UserPromptSubmit`	The user submits a prompt, before Claude sees it. Can block or inject context.	ref	user-prompt-submit/	`write-event-marker` · `update-counts` · `flush-transcript-chunk`
`UserPromptExpansion`	A slash command / skill prompt is expanded/templated before use.	ref	user-prompt-expansion/	ignored — Slash-command expansion — redundant with `UserPromptSubmit`.

Tool lifecycle

Hook	Fires when	Docs	Examples	What we do
`PreToolUse`	Before a tool executes — `tool_name` + `tool_input` available. Can block or modify the input.	ref	pre-tool-use/	ignored — Blocking pre-hook; an observe-only writer gains nothing — `PostToolUse` captures the outcome.
`PermissionRequest`	A permission dialog is about to be shown for a tool call.	ref	permission-request/	ignored — Permission-dialog control hook, not session history.
`PermissionDenied`	A tool call was denied (auto-classifier or user).	ref	permission-denied/	ignored — Permission control event, not session history.
`PostToolUse`	A tool succeeds — `tool_output` available. Can post-process the result.	ref	post-tool-use/	`write-event-marker` · `update-counts` · `flush-transcript-chunk`
`PostToolUseFailure`	A tool fails — `error_message` available.	ref	post-tool-use-failure/	`write-event-marker` · `update-counts` · `flush-transcript-chunk`
`PostToolBatch`	A batch of parallel tool calls resolves.	ref	post-tool-batch/	ignored — Batch boundary; the individual `PostToolUse` events are already captured.

Subagents, teams & tasks

Hook	Fires when	Docs	Examples	What we do
`SubagentStart`	A subagent is spawned — `agent_type`, `agent_id`, `task_description`.	ref	subagent-start/	`write-event-marker` · `update-counts`
`SubagentStop`	A subagent finishes — `summary` of its work.	ref	subagent-stop/	`write-event-marker` · `update-counts`
`TeammateIdle`	A team teammate goes idle.	ref	teammate-idle/	ignored — Team orchestration, not session history.
`TaskCreated`	A task is created via `TaskCreate`.	ref	task-created/	ignored — Task orchestration, not session history.
`TaskCompleted`	A task is marked complete.	ref	task-completed/	ignored — Task orchestration, not session history.

Display, MCP & notifications

Hook	Fires when	Docs	Examples	What we do
`MessageDisplay`	An assistant message is streamed/displayed to the user.	ref	message-display/	ignored — UX event; the message content is already in the transcript.
`Elicitation`	An MCP server requests user input.	ref	elicitation/	ignored — MCP interaction control hook; an observe-only writer gains nothing.
`ElicitationResult`	The user responds to an elicitation.	ref	elicitation-result/	ignored — MCP interaction event; the content is in the transcript.
`Notification`	Claude Code emits a notification (`permission_prompt`, `idle_prompt`, `auth_success`, …).	ref	notification/	ignored — UX notification, not session history.

Environment, config & files

Hook	Fires when	Docs	Examples	What we do
`CwdChanged`	The working directory changes during a session.	ref	cwd-changed/	ignored — Host signal, out of session scope.
`FileChanged`	A watched file changes on disk.	ref	file-changed/	ignored — Watcher signal, out of session scope.
`ConfigChange`	A settings/config/skills file changes during the session (`user_settings`, `project_settings`, …).	ref	config-change/	ignored — Config-change signal, out of session scope.

Worktrees

Hook	Fires when	Docs	Examples	What we do
`WorktreeCreate`	A git worktree is created (`--worktree`).	ref	worktree-create/	ignored — Git-worktree lifecycle, irrelevant to session logging.
`WorktreeRemove`	A git worktree is removed.	ref	worktree-remove/	ignored — Git-worktree lifecycle, irrelevant to session logging.

Compaction

Hook	Fires when	Docs	Examples	What we do
`PreCompact`	Before context compaction — `trigger` ∈ `manual`/`auto`.	ref	pre-compact/	`write-event-marker`
`PostCompact`	After compaction completes — `trigger` ∈ `manual`/`auto`.	ref	post-compact/	`write-event-marker`

Turn end

Hook	Fires when	Docs	Examples	What we do
`Stop`	Claude finishes responding to a turn — `turn_number`, `assistant_message`.	ref	stop/	`write-event-marker` · `flush-transcript-chunk`
`StopFailure`	A turn ends with an API error — `rate_limit`, `overloaded`, `max_output_tokens`, … A turn-level failure (see the crash note in the doc).	ref	stop-failure/	`write-event-marker` · `update-counts`

Session end

Hook	Fires when	Docs	Examples	What we do
`SessionEnd`	The session terminates — `reason` ∈ `clear`/`resume`/`logout`/`prompt_input_exit`/`bypass_permissions_disabled`/`other`.	ref	session-end/	`flush-transcript-chunk` · `write-summary` · `upload-blobs`

On crashes. There is no dedicated "session crashed" event. Abnormal termination surfaces in three ways, in increasing severity:

StopFailure — the turn hit an API/runtime error but the session is alive.
SessionEnd with reason: "other" — an orderly-but-non-standard shutdown.
No SessionEnd at all — a hard crash / kill. The session is then detected as incomplete by derivation (see couchdb.md → status model) and finalised by the reconcile utility (tools.md). Fixtures for (1) and (2) live under stop-failure/ and session-end/; case (3) is exercised by leaving a started session with no end fixture.

Coverage vs. what we wire today

We currently bind actions to 11 of the 30 events — SessionStart, UserPromptSubmit, PostToolUse, PostToolUseFailure, SubagentStart, SubagentStop, PreCompact, PostCompact, Stop, StopFailure, SessionEnd. The rest are intentionally ignored — the "What we do" column gives the reason per event: a passive, observe-only writer gains nothing from blocking / UX / orchestration hooks, and every hook invocation costs a Bun startup, so we wire only the events that carry the session record (actions.md). Wiring an ignored event = add the action + binding in the blueprint, then regenerate hooks.json (bun run gen:hooks).

Field-shape caveat. Payload field names/casing follow the official reference at authoring time. Claude Code is upstream and evolving; when in doubt, capture a real payload (every hook just receives JSON on stdin — … | tee fixture.json) and reconcile against the official reference.