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HomeDocsClaude Code CLI 20 Aug 2026
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Intercept and control agent behavior with hooks changedagent-sdk/hooks

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216216SDK matchers follow the same rules as [matchers in settings files](/docs/en/hooks#matcher-patterns). That section documents the exact-string and regular-expression evaluation paths, their version requirements, and the matcher values for each event type.
217217 
218| Option | Type | Default | Description |
219| --------- | ---------------- | ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
220| `matcher` | `string` | `undefined` | Pattern matched against the event's filter field, following the [rules for matchers in settings files](/docs/en/hooks#matcher-patterns). For tool hooks, this is the tool name. Built-in tools include `Bash`, `Read`, `Write`, `Edit`, `Glob`, `Grep`, `WebFetch`, `Agent`, and others (see [Tool Input Types](/docs/en/agent-sdk/typescript#tool-input-types) for the full list). MCP tools use the pattern `mcp__<server>__<action>`. |
221| `hooks` | `HookCallback[]` | - | Required. Array of callback functions to execute when the pattern matches |
222| `timeout` | `number` | `undefined` | Timeout in seconds. When omitted, Claude Code applies the [event's default timeout](#hook-timeout). Your SDK callbacks follow the `command` hook defaults |
218| Option | Type | Default | Description |
219| --------- | ---------------- | ----------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
220| `matcher` | `string` | `undefined` | Pattern matched against the event's filter field, following the [rules for matchers in settings files](/docs/en/hooks#matcher-patterns). For tool hooks, this is the tool name. Built-in tools include `Bash`, `Read`, `Write`, `Edit`, `Glob`, `Grep`, `WebFetch`, `Agent`, and others (see [Tool Input Types](/docs/en/agent-sdk/typescript#tool-input-types) for the full list). MCP tools use the pattern `mcp__<server>__<action>`, where `<server>` is the key you use in the `mcpServers` configuration. |
221| `hooks` | `HookCallback[]` | - | Required. Array of callback functions to execute when the pattern matches |
222| `timeout` | `number` | `undefined` | Timeout in seconds. When omitted, Claude Code applies the [event's default timeout](#hook-timeout). Your SDK callbacks follow the `command` hook defaults |
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224Use the `matcher` pattern to target specific tools whenever possible. A matcher with `'Bash'` only runs for Bash commands, while omitting the pattern runs your callbacks for every occurrence of the event.
225 
226<Tip>
227 **Discovering tool names:** See [Tool Input Types](/docs/en/agent-sdk/typescript#tool-input-types) for the full list of built-in tool names, or add a hook without a matcher to log all tool calls your session makes.
228 
229 **MCP tool naming:** MCP tools always start with `mcp__` followed by the server name and action: `mcp__<server>__<action>`. For example, if you configure a server named `playwright`, its tools are named `mcp__playwright__browser_screenshot`, `mcp__playwright__browser_click`, and so on. The server name comes from the key you use in the `mcpServers` configuration.
230</Tip>
224Use the `matcher` pattern to target specific tools whenever possible. A matcher with `'Bash'` only runs for Bash commands, while omitting the pattern runs your callbacks for every occurrence of the event. Omit it on purpose to log every tool call your session makes.
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232226### Callback functions
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