Hooks reference changedhooks
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988988* [Stop](#stop) and [SubagentStop](#subagentstop): at the end of the turn. The conversation continues so Claude can act on the feedback. See [Stop decision control](#stop-decision-control)
989989* [PostModelSwitch](#postmodelswitch): with the next request after the switch. See [PostModelSwitch decision control](#postmodelswitch-decision-control) for timing
990990
991When several hooks return `additionalContext` for the same event, Claude receives all of the values. If a value exceeds 10,000 characters, Claude Code writes the full text to a file in the session directory and passes Claude the file path with a short preview instead.
991When several hooks return `additionalContext` for the same event, Claude receives all of the values.
992992
993If a value exceeds 10,000 characters, Claude Code writes the text to a file in the session directory and passes Claude the file path with a short preview instead.
994
993995Use `additionalContext` for information Claude should know about the current state of your environment or the operation that just ran:
994996
995997* **Environment state**: the current branch, deployment target, or active feature flags
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11021104
11031105Before v2.1.214, forked sessions reported source `"resume"`.
11041106
1107When you run `/clear` in an interactive session, the matching SessionStart hooks run in the background and the prompt accepts input again right away. Claude's first response still waits for the hooks to finish, so their context reaches Claude. If you run `/clear` again or switch to another conversation with a command such as `/resume` while those hooks are still running, Claude Code cancels them and discards their output.
1108
11051109#### SessionStart input
11061110
11071111In addition to the [common input fields](#common-input-fields), SessionStart hooks receive `source` and optionally `model`, `agent_type`, and `session_title`:
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22862290
22872291### SubagentStart
22882292
2289Runs when a Claude Code subagent is spawned via the Agent tool. Supports matchers to filter by agent type name. For built-in agents, this is the agent name like `general-purpose`, `Explore`, or `Plan`. For [custom subagents](/docs/en/sub-agents), this is the `name` field from the agent's frontmatter, not the filename.
2293Runs when Claude spawns a subagent with the Agent tool, when Claude [resumes a subagent](/docs/en/sub-agents#resume-subagents), and each time an in-process [agent team](/docs/en/agent-teams) teammate handles a new message. Supports matchers to filter by agent type name. For built-in agents, this is the agent name like `general-purpose`, `Explore`, or `Plan`. For [custom subagents](/docs/en/sub-agents), this is the `name` field from the agent's frontmatter, not the filename.
22902294
22912295For subagents shipped by a [plugin](/docs/en/plugins), the agent type is the plugin-scoped identifier such as `my-plugin:reviewer`, not the bare frontmatter name. The colon places a plugin-scoped name on the regular-expression path, so anchor the matcher with `^` and `$` for an exact match: `^my-plugin:reviewer$`.
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23202324}
23212325```
23222326
2327When the hook runs again for the same subagent, Claude Code injects the returned context only when the subagent's context doesn't already hold the copy from an earlier run. The copy injected at launch stays in place, leaving the subagent's [prompt cache](/docs/en/prompt-caching#subagents-and-the-cache) intact. After [auto-compaction](/docs/en/sub-agents#auto-compaction) discards that copy, Claude Code injects the next run's context again.
2328
23232329### SubagentStop
23242330
23252331Runs when a Claude Code subagent has finished responding. Matches on agent type, same values as SubagentStart.
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27772783 "session_id": "abc123",
27782784 "transcript_path": "/Users/.../.claude/projects/.../transcript.jsonl",
27792785 "cwd": "/Users/my-project",
2780 "hook_event_name": "DirectoryAdded",
2781 "directory": "/Users/my-other-repo",
2782 "source": "slash_command"
2783}
2784```
2785
2786DirectoryAdded hooks have no decision control. They can't block the add, which has already completed when the hook runs. Claude Code discards the `continue` field from their JSON output and surfaces the rest differently per source:
2787
2788* `slash_command`: Claude Code delivers the hook's `systemMessage` to Claude as context on the next conversation turn, rather than showing it to you. A count of failed hooks appears in the transcript. Full failure output goes to the debug log
2789* `register_repo_root`: Claude Code writes `systemMessage` output and failure output to the debug log only
2790
2791### FileChanged
2792
2793Runs when a watched file changes on disk. Claude Code detects changes with a filesystem watcher, not by inspecting tool calls, so it runs the hook no matter what changed the file: an `Edit` or `Write` tool call, a script Claude runs with `Bash`, or a process outside Claude Code entirely. A common use is reloading environment variables when proje
2786 "hook_event_name": "DirectoryAdde
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