Gemini CLI hooks

Hooks are scripts or programs that Gemini CLI executes at specific points in the agentic loop, allowing you to intercept and customize behavior without modifying the CLI’s source code.

See writing hooks guide for a tutorial on creating your first hook and a comprehensive example.

See hooks reference for the technical specification of the I/O schemas.

See best practices for guidelines on security, performance, and debugging.

What are hooks?

With hooks, you can:

• Add context: Inject relevant information before the model processes a request
• Validate actions: Review and block potentially dangerous operations
• Enforce policies: Implement security and compliance requirements
• Log interactions: Track tool usage and model responses
• Optimize behavior: Dynamically adjust tool selection or model parameters

Hooks run synchronously as part of the agent loop—when a hook event fires, Gemini CLI waits for all matching hooks to complete before continuing.

Core concepts

Hook events

Hooks are triggered by specific events in Gemini CLI’s lifecycle. The following table lists all available hook events:

Event	When It Fires	Common Use Cases
SessionStart	When a session begins	Initialize resources, load context
SessionEnd	When a session ends	Clean up, save state
BeforeAgent	After user submits prompt, before planning	Add context, validate prompts
AfterAgent	When agent loop ends	Review output, force continuation
BeforeModel	Before sending request to LLM	Modify prompts, add instructions
AfterModel	After receiving LLM response	Filter responses, log interactions
BeforeToolSelection	Before LLM selects tools (after BeforeModel)	Filter available tools, optimize selection
BeforeTool	Before a tool executes	Validate arguments, block dangerous ops
AfterTool	After a tool executes	Process results, run tests
PreCompress	Before context compression	Save state, notify user
Notification	When a notification occurs (e.g., permission)	Auto-approve, log decisions

Hook types

Gemini CLI currently supports command hooks that run shell commands or scripts:

{
  "type": "command",
  "command": "$GEMINI_PROJECT_DIR/.gemini/hooks/my-hook.sh",
  "timeout": 30000
}

Note: Plugin hooks (npm packages) are planned for a future release.

Matchers

For tool-related events (BeforeTool, AfterTool), you can filter which tools trigger the hook:

{
  "hooks": {
    "BeforeTool": [
      {
        "matcher": "write_file|replace",
        "hooks": [
          /* hooks for write operations */
        ]
      }
    ]
  }
}

Matcher patterns:

• Exact match: "read_file" matches only read_file
• Regex: "write_.*|replace" matches write_file, replace
• Wildcard: "*" or "" matches all tools

Session event matchers:

• SessionStart: startup, resume, clear
• SessionEnd: exit, clear, logout, prompt_input_exit
• PreCompress: manual, auto
• Notification: ToolPermission

Hook input/output contract

Command hook communication

Hooks communicate via:

• Input: JSON on stdin
• Output: Exit code + stdout/stderr

Exit codes

• 0: Success - stdout shown to user (or injected as context for some events)
• 2: Blocking error - stderr shown to agent/user, operation may be blocked
• Other: Non-blocking warning - logged but execution continues

Common input fields

Every hook receives these base fields:

{
  "session_id": "abc123",
  "transcript_path": "/path/to/transcript.jsonl",
  "cwd": "/path/to/project",
  "hook_event_name": "BeforeTool",
  "timestamp": "2025-12-01T10:30:00Z"
  // ... event-specific fields
}

Event-specific fields

BeforeTool

Input:

{
  "tool_name": "write_file",
  "tool_input": {
    "file_path": "/path/to/file.ts",
    "content": "..."
  }
}

Output (JSON on stdout):

{
  "decision": "allow|deny|ask|block",
  "reason": "Explanation shown to agent",
  "systemMessage": "Message shown to user"
}

Or simple exit codes:

• Exit 0 = allow (stdout shown to user)
• Exit 2 = deny (stderr shown to agent)

AfterTool

Input:

{
  "tool_name": "read_file",
  "tool_input": { "file_path": "..." },
  "tool_response": "file contents..."
}

Output:

{
  "decision": "allow|deny",
  "hookSpecificOutput": {
    "hookEventName": "AfterTool",
    "additionalContext": "Extra context for agent"
  }
}

BeforeAgent

Input:

{
  "prompt": "Fix the authentication bug"
}

Output:

{
  "decision": "allow|deny",
  "hookSpecificOutput": {
    "hookEventName": "BeforeAgent",
    "additionalContext": "Recent project decisions: ..."
  }
}

BeforeModel

Input:

{
  "llm_request": {
    "model": "gemini-2.0-flash-exp",
    "messages": [{ "role": "user", "content": "Hello" }],
    "config": { "temperature": 0.7 },
    "toolConfig": {
      "functionCallingConfig": {
        "mode": "AUTO",
        "allowedFunctionNames": ["read_file", "write_file"]
      }
    }
  }
}

Output:

{
  "decision": "allow",
  "hookSpecificOutput": {
    "hookEventName": "BeforeModel",
    "llm_request": {
      "messages": [
        { "role": "system", "content": "Additional instructions..." },
        { "role": "user", "content": "Hello" }
      ]
    }
  }
}

AfterModel

Input:

{
  "llm_request": {
    "model": "gemini-2.0-flash-exp",
    "messages": [
      /* ... */
    ],
    "config": {
      /* ... */
    },
    "toolConfig": {
      /* ... */
    }
  },
  "llm_response": {
    "text": "string",
    "candidates": [
      {
        "content": {
          "role": "model",
          "parts": ["array of content parts"]
        },
        "finishReason": "STOP"
      }
    ]
  }
}

Output:

{
  "hookSpecificOutput": {
    "hookEventName": "AfterModel",
    "llm_response": {
      "candidate": {
        /* modified response */
      }
    }
  }
}

BeforeToolSelection

Input:

{
  "llm_request": {
    "model": "gemini-2.0-flash-exp",
    "messages": [
      /* ... */
    ],
    "toolConfig": {
      "functionCallingConfig": {
        "mode": "AUTO",
        "allowedFunctionNames": [
          /* 100+ tools */
        ]
      }
    }
  }
}

Output:

{
  "hookSpecificOutput": {
    "hookEventName": "BeforeToolSelection",
    "toolConfig": {
      "functionCallingConfig": {
        "mode": "ANY",
        "allowedFunctionNames": ["read_file", "write_file", "replace"]
      }
    }
  }
}

Or simple output (comma-separated tool names sets mode to ANY):

echo "read_file,write_file,replace"

SessionStart

Input:

{
  "source": "startup|resume|clear"
}

Output:

{
  "hookSpecificOutput": {
    "hookEventName": "SessionStart",
    "additionalContext": "Loaded 5 project memories"
  }
}

SessionEnd

Input:

{
  "reason": "exit|clear|logout|prompt_input_exit|other"
}

No structured output expected (but stdout/stderr logged).

PreCompress

Input:

{
  "trigger": "manual|auto"
}

Output:

{
  "systemMessage": "Compression starting..."
}

Notification

Input:

{
  "notification_type": "ToolPermission",
  "message": "string",
  "details": {
    /* notification details */
  }
}

Output:

{
  "systemMessage": "Notification logged"
}

Configuration

Hook definitions are configured in settings.json files using the hooks object. Configuration can be specified at multiple levels with defined precedence rules.

Configuration layers

Hook configurations are applied in the following order of execution (lower numbers run first):

1. Project settings: .gemini/settings.json in your project directory (highest priority)
2. User settings: ~/.gemini/settings.json
3. System settings: /etc/gemini-cli/settings.json
4. Extensions: Internal hooks defined by installed extensions (lowest priority)

Deduplication and shadowing

If multiple hooks with the identical name and command are discovered across different configuration layers, Gemini CLI deduplicates them. The hook from the higher-priority layer (e.g., Project) will be kept, and others will be ignored.

Within each level, hooks run in the order they are declared in the configuration.

Configuration schema

{
  "hooks": {
    "EventName": [
      {
        "matcher": "pattern",
        "hooks": [
          {
            "name": "hook-identifier",
            "type": "command",
            "command": "./path/to/script.sh",
            "description": "What this hook does",
            "timeout": 30000
          }
        ]
      }
    ]
  }
}

Configuration properties:

• name (string, recommended): Unique identifier for the hook used in /hooks enable/disable commands. If omitted, the command path is used as the identifier.
• type (string, required): Hook type - currently only "command" is supported
• command (string, required): Path to the script or command to execute
• description (string, optional): Human-readable description shown in /hooks panel
• timeout (number, optional): Timeout in milliseconds (default: 60000)
• matcher (string, optional): Pattern to filter when hook runs (event matchers only)

Environment variables

Hooks have access to:

• GEMINI_PROJECT_DIR: Project root directory
• GEMINI_SESSION_ID: Current session ID
• GEMINI_API_KEY: Gemini API key (if configured)
• All other environment variables from the parent process

Managing hooks

View registered hooks

Use the /hooks panel command to view all registered hooks:

/hooks panel

This command displays:

• All active hooks organized by event
• Hook source (user, project, system)
• Hook type (command or plugin)
• Execution status and recent output

Enable and disable hooks

You can temporarily enable or disable individual hooks using commands:

/hooks enable hook-name
/hooks disable hook-name

These commands allow you to control hook execution without editing configuration files. The hook name should match the name field in your hook configuration. Changes made via these commands are persisted to your global User settings (~/.gemini/settings.json).

Disabled hooks configuration

To permanently disable hooks, add them to the hooks.disabled array in your settings.json:

{
  "hooks": {
    "disabled": ["secret-scanner", "auto-test"]
  }
}

Note: The hooks.disabled array uses a UNION merge strategy. Disabled hooks from all configuration levels (user, project, system) are combined and deduplicated, meaning a hook disabled at any level remains disabled.

Migration from Claude Code

If you have hooks configured for Claude Code, you can migrate them:

gemini hooks migrate --from-claude

This command:

• Reads .claude/settings.json
• Converts event names (PreToolUse → BeforeTool, etc.)
• Translates tool names (Bash → run_shell_command, replace → replace)
• Updates matcher patterns
• Writes to .gemini/settings.json

Event name mapping

Claude Code	Gemini CLI
PreToolUse	BeforeTool
PostToolUse	AfterTool
UserPromptSubmit	BeforeAgent
Stop	AfterAgent
Notification	Notification
SessionStart	SessionStart
SessionEnd	SessionEnd
PreCompact	PreCompress

Tool name mapping

Claude Code	Gemini CLI
Bash	run_shell_command
Edit	replace
Read	read_file
Write	write_file
Glob	glob
Grep	search_file_content
LS	list_directory

Tool and Event Matchers Reference

Available tool names for matchers

The following built-in tools can be used in BeforeTool and AfterTool hook matchers:

File operations

• read_file - Read a single file
• read_many_files - Read multiple files at once
• write_file - Create or overwrite a file
• replace - Edit file content with find/replace

File system

• list_directory - List directory contents
• glob - Find files matching a pattern
• search_file_content - Search within file contents

Execution

• run_shell_command - Execute shell commands

Web and external

• google_web_search - Google Search with grounding
• web_fetch - Fetch web page content

Agent features

• write_todos - Manage TODO items
• save_memory - Save information to memory
• delegate_to_agent - Delegate tasks to sub-agents

Example matchers

{
  "matcher": "write_file|replace" // File editing tools
}

{
  "matcher": "read_.*" // All read operations
}

{
  "matcher": "run_shell_command" // Only shell commands
}

{
  "matcher": "*" // All tools
}

Event-specific matchers

SessionStart event matchers

• startup - Fresh session start
• resume - Resuming a previous session
• clear - Session cleared

SessionEnd event matchers

• exit - Normal exit
• clear - Session cleared
• logout - User logged out
• prompt_input_exit - Exit from prompt input
• other - Other reasons

PreCompress event matchers

• manual - Manually triggered compression
• auto - Automatically triggered compression

Notification event matchers

• ToolPermission - Tool permission notifications

Learn more

• Writing Hooks - Tutorial and comprehensive example
• Best Practices - Security, performance, and debugging
• Custom Commands - Create reusable prompt shortcuts
• Configuration - Gemini CLI configuration options