feat: Add tool permission and hook callbacks support (#143)

## Summary

Adds comprehensive support for tool permission callbacks and hook
callbacks to the Python SDK, enabling fine-grained control over tool
execution and custom event handling.

## Key Changes

- **Tool Permission Callbacks**: Control which tools Claude can use and
modify their inputs
  -  type with async support
  -  with suggestions from CLI
  -  for structured responses
  
- **Hook Callbacks**: React to events in the Claude workflow
  -  type for event handlers
  -  for conditional hook execution
  - Support for tool_use_start, tool_use_end events
  
- **Integration**: Full plumbing through ClaudeCodeOptions → Client →
Query
- **Examples**: Comprehensive example showing permission control
patterns
- **Tests**: Coverage for all callback scenarios

## Implementation Details

- Callbacks are registered during initialization phase
- Control protocol handles can_use_tool and hook_callback requests
- Backwards compatible with dict returns for tool permissions
- Proper error handling and type safety throughout

Builds on top of #139's control protocol implementation.

---------

Co-authored-by: Dickson Tsai <dickson@anthropic.com>

examples/tool_permission_callback.py

@@ -0,0 +1,158 @@
+#!/usr/bin/env python3
+"""Example: Tool Permission Callbacks.
+
+This example demonstrates how to use tool permission callbacks to control
+which tools Claude can use and modify their inputs.
+"""
+
+import asyncio
+import json
+
+from claude_code_sdk import (
+    AssistantMessage,
+    ClaudeCodeOptions,
+    ClaudeSDKClient,
+    PermissionResultAllow,
+    PermissionResultDeny,
+    ResultMessage,
+    TextBlock,
+    ToolPermissionContext,
+)
+
+# Track tool usage for demonstration
+tool_usage_log = []
+
+
+async def my_permission_callback(
+    tool_name: str,
+    input_data: dict,
+    context: ToolPermissionContext
+) -> PermissionResultAllow | PermissionResultDeny:
+    """Control tool permissions based on tool type and input."""
+
+    # Log the tool request
+    tool_usage_log.append({
+        "tool": tool_name,
+        "input": input_data,
+        "suggestions": context.suggestions
+    })
+
+    print(f"\n🔧 Tool Permission Request: {tool_name}")
+    print(f"   Input: {json.dumps(input_data, indent=2)}")
+
+    # Always allow read operations
+    if tool_name in ["Read", "Glob", "Grep"]:
+        print(f"   ✅ Automatically allowing {tool_name} (read-only operation)")
+        return PermissionResultAllow()
+
+    # Deny write operations to system directories
+    if tool_name in ["Write", "Edit", "MultiEdit"]:
+        file_path = input_data.get("file_path", "")
+        if file_path.startswith("/etc/") or file_path.startswith("/usr/"):
+            print(f"   ❌ Denying write to system directory: {file_path}")
+            return PermissionResultDeny(
+                message=f"Cannot write to system directory: {file_path}"
+            )
+
+        # Redirect writes to a safe directory
+        if not file_path.startswith("/tmp/") and not file_path.startswith("./"):
+            safe_path = f"./safe_output/{file_path.split('/')[-1]}"
+            print(f"   ⚠️  Redirecting write from {file_path} to {safe_path}")
+            modified_input = input_data.copy()
+            modified_input["file_path"] = safe_path
+            return PermissionResultAllow(
+                updatedInput=modified_input
+            )
+
+    # Check dangerous bash commands
+    if tool_name == "Bash":
+        command = input_data.get("command", "")
+        dangerous_commands = ["rm -rf", "sudo", "chmod 777", "dd if=", "mkfs"]
+
+        for dangerous in dangerous_commands:
+            if dangerous in command:
+                print(f"   ❌ Denying dangerous command: {command}")
+                return PermissionResultDeny(
+                    message=f"Dangerous command pattern detected: {dangerous}"
+                )
+
+        # Allow but log the command
+        print(f"   ✅ Allowing bash command: {command}")
+        return PermissionResultAllow()
+
+    # For all other tools, ask the user
+    print(f"   ❓ Unknown tool: {tool_name}")
+    print(f"      Input: {json.dumps(input_data, indent=6)}")
+    user_input = input("   Allow this tool? (y/N): ").strip().lower()
+
+    if user_input in ("y", "yes"):
+        return PermissionResultAllow()
+    else:
+        return PermissionResultDeny(
+            message="User denied permission"
+        )
+
+
+async def main():
+    """Run example with tool permission callbacks."""
+
+    print("=" * 60)
+    print("Tool Permission Callback Example")
+    print("=" * 60)
+    print("\nThis example demonstrates how to:")
+    print("1. Allow/deny tools based on type")
+    print("2. Modify tool inputs for safety")
+    print("3. Log tool usage")
+    print("4. Prompt for unknown tools")
+    print("=" * 60)
+
+    # Configure options with our callback
+    options = ClaudeCodeOptions(
+        can_use_tool=my_permission_callback,
+        # Use default permission mode to ensure callbacks are invoked
+        permission_mode="default",
+        cwd="."  # Set working directory
+    )
+
+    # Create client and send a query that will use multiple tools
+    async with ClaudeSDKClient(options) as client:
+        print("\n📝 Sending query to Claude...")
+        await client.query(
+            "Please do the following:\n"
+            "1. List the files in the current directory\n"
+            "2. Create a simple Python hello world script at hello.py\n"
+            "3. Run the script to test it"
+        )
+
+        print("\n📨 Receiving response...")
+        message_count = 0
+
+        async for message in client.receive_response():
+            message_count += 1
+
+            if isinstance(message, AssistantMessage):
+                # Print Claude's text responses
+                for block in message.content:
+                    if isinstance(block, TextBlock):
+                        print(f"\n💬 Claude: {block.text}")
+
+            elif isinstance(message, ResultMessage):
+                print("\n✅ Task completed!")
+                print(f"   Duration: {message.duration_ms}ms")
+                if message.total_cost_usd:
+                    print(f"   Cost: ${message.total_cost_usd:.4f}")
+                print(f"   Messages processed: {message_count}")
+
+    # Print tool usage summary
+    print("\n" + "=" * 60)
+    print("Tool Usage Summary")
+    print("=" * 60)
+    for i, usage in enumerate(tool_usage_log, 1):
+        print(f"\n{i}. Tool: {usage['tool']}")
+        print(f"   Input: {json.dumps(usage['input'], indent=6)}")
+        if usage['suggestions']:
+            print(f"   Suggestions: {usage['suggestions']}")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())

src/claude_code_sdk/__init__.py

@@ -16,16 +16,25 @@ from .client import ClaudeSDKClient
 from .query import query
 from .types import (
     AssistantMessage,
+    CanUseTool,
     ClaudeCodeOptions,
     ContentBlock,
+    HookCallback,
+    HookContext,
+    HookMatcher,
     McpSdkServerConfig,
     McpServerConfig,
     Message,
     PermissionMode,
+    PermissionResult,
+    PermissionResultAllow,
+    PermissionResultDeny,
+    PermissionUpdate,
     ResultMessage,
     SystemMessage,
     TextBlock,
     ThinkingBlock,
+    ToolPermissionContext,
     ToolResultBlock,
     ToolUseBlock,
     UserMessage,
@@ -286,6 +295,16 @@ __all__ = [
     "ToolUseBlock",
     "ToolResultBlock",
     "ContentBlock",
+    # Tool callbacks
+    "CanUseTool",
+    "ToolPermissionContext",
+    "PermissionResult",
+    "PermissionResultAllow",
+    "PermissionResultDeny",
+    "PermissionUpdate",
+    "HookCallback",
+    "HookContext",
+    "HookMatcher",
     # MCP Server Support
     "create_sdk_mcp_server",
     "tool",

src/claude_code_sdk/_internal/client.py

@@ -19,6 +19,22 @@ class InternalClient:
     def __init__(self) -> None:
         """Initialize the internal client."""
 
+    def _convert_hooks_to_internal_format(
+        self, hooks: dict[str, list]
+    ) -> dict[str, list[dict[str, Any]]]:
+        """Convert HookMatcher format to internal Query format."""
+        internal_hooks = {}
+        for event, matchers in hooks.items():
+            internal_hooks[event] = []
+            for matcher in matchers:
+                # Convert HookMatcher to internal dict format
+                internal_matcher = {
+                    "matcher": matcher.matcher if hasattr(matcher, 'matcher') else None,
+                    "hooks": matcher.hooks if hasattr(matcher, 'hooks') else []
+                }
+                internal_hooks[event].append(internal_matcher)
+        return internal_hooks
+
     async def process_query(
         self,
         prompt: str | AsyncIterable[dict[str, Any]],
@@ -48,8 +64,8 @@ class InternalClient:
         query = Query(
             transport=chosen_transport,
             is_streaming_mode=is_streaming,
-            can_use_tool=None,  # TODO: Add support for can_use_tool callback
-            hooks=None,  # TODO: Add support for hooks
+            can_use_tool=options.can_use_tool,
+            hooks=self._convert_hooks_to_internal_format(options.hooks) if options.hooks else None,
             sdk_mcp_servers=sdk_mcp_servers,
         )
 

src/claude_code_sdk/_internal/query.py

@@ -15,10 +15,14 @@ from mcp.types import (
 )
 
 from ..types import (
+    PermissionResult,
+    PermissionResultAllow,
+    PermissionResultDeny,
     SDKControlPermissionRequest,
     SDKControlRequest,
     SDKControlResponse,
     SDKHookCallbackRequest,
+    ToolPermissionContext,
 )
 from .transport import Transport
 
@@ -195,15 +199,34 @@ class Query:
                 if not self.can_use_tool:
                     raise Exception("canUseTool callback is not provided")
 
-                response_data = await self.can_use_tool(
+                context = ToolPermissionContext(
+                    signal=None,  # TODO: Add abort signal support
+                    suggestions=permission_request.get("permission_suggestions", [])
+                )
+
+                response = await self.can_use_tool(
                     permission_request["tool_name"],
                     permission_request["input"],
-                    {
-                        "signal": None,  # TODO: Add abort signal support
-                        "suggestions": permission_request.get("permission_suggestions"),
-                    },
+                    context
                 )
 
+                # Convert PermissionResult to expected dict format
+                if isinstance(response, PermissionResultAllow):
+                    response_data = {
+                        "allow": True
+                    }
+                    if response.updatedInput is not None:
+                        response_data["input"] = response.updatedInput
+                    # TODO: Handle updatedPermissions when control protocol supports it
+                elif isinstance(response, PermissionResultDeny):
+                    response_data = {
+                        "allow": False,
+                        "reason": response.message
+                    }
+                    # TODO: Handle interrupt flag when control protocol supports it
+                else:
+                    raise TypeError(f"Tool permission callback must return PermissionResult (PermissionResultAllow or PermissionResultDeny), got {type(response)}")
+
             elif subtype == "hook_callback":
                 hook_callback_request: SDKHookCallbackRequest = request_data  # type: ignore[assignment]
                 # Handle hook callback

src/claude_code_sdk/client.py

@@ -100,6 +100,22 @@ class ClaudeSDKClient:
         self._query: Any | None = None
         os.environ["CLAUDE_CODE_ENTRYPOINT"] = "sdk-py-client"
 
+    def _convert_hooks_to_internal_format(
+        self, hooks: dict[str, list]
+    ) -> dict[str, list[dict[str, Any]]]:
+        """Convert HookMatcher format to internal Query format."""
+        internal_hooks = {}
+        for event, matchers in hooks.items():
+            internal_hooks[event] = []
+            for matcher in matchers:
+                # Convert HookMatcher to internal dict format
+                internal_matcher = {
+                    "matcher": matcher.matcher if hasattr(matcher, 'matcher') else None,
+                    "hooks": matcher.hooks if hasattr(matcher, 'hooks') else []
+                }
+                internal_hooks[event].append(internal_matcher)
+        return internal_hooks
+
     async def connect(
         self, prompt: str | AsyncIterable[dict[str, Any]] | None = None
     ) -> None:
@@ -135,8 +151,8 @@ class ClaudeSDKClient:
         self._query = Query(
             transport=self._transport,
             is_streaming_mode=True,  # ClaudeSDKClient always uses streaming mode
-            can_use_tool=None,  # TODO: Add support for can_use_tool callback
-            hooks=None,  # TODO: Add support for hooks
+            can_use_tool=self.options.can_use_tool,
+            hooks=self._convert_hooks_to_internal_format(self.options.hooks) if self.options.hooks else None,
             sdk_mcp_servers=sdk_mcp_servers,
         )
 

src/claude_code_sdk/types.py

@@ -1,10 +1,14 @@
 """Type definitions for Claude SDK."""
 
+from collections.abc import Awaitable, Callable
 from dataclasses import dataclass, field
 from pathlib import Path
 from typing import TYPE_CHECKING, Any, Literal, TypedDict
 
-from typing_extensions import NotRequired  # For Python < 3.11 compatibility
+try:
+    from typing import NotRequired  # Python 3.11+
+except ImportError:
+    from typing_extensions import NotRequired  # For Python < 3.11 compatibility
 
 if TYPE_CHECKING:
     from mcp.server import Server as McpServer
@@ -13,6 +17,87 @@ if TYPE_CHECKING:
 PermissionMode = Literal["default", "acceptEdits", "plan", "bypassPermissions"]
 
 
+# Permission Update types (matching TypeScript SDK)
+PermissionUpdateDestination = Literal[
+    "userSettings",
+    "projectSettings", 
+    "localSettings",
+    "session"
+]
+
+PermissionBehavior = Literal["allow", "deny", "ask"]
+
+@dataclass
+class PermissionRuleValue:
+    """Permission rule value."""
+    toolName: str
+    ruleContent: str | None = None
+
+@dataclass 
+class PermissionUpdate:
+    """Permission update configuration."""
+    type: Literal["addRules", "replaceRules", "removeRules", "setMode", "addDirectories", "removeDirectories"]
+    rules: list[PermissionRuleValue] | None = None
+    behavior: PermissionBehavior | None = None
+    mode: PermissionMode | None = None
+    directories: list[str] | None = None
+    destination: PermissionUpdateDestination | None = None
+
+# Tool callback types
+@dataclass
+class ToolPermissionContext:
+    """Context information for tool permission callbacks."""
+
+    signal: Any | None = None  # Future: abort signal support
+    suggestions: list[PermissionUpdate] = field(default_factory=list)  # Permission suggestions from CLI
+
+
+# Match TypeScript's PermissionResult structure
+@dataclass
+class PermissionResultAllow:
+    """Allow permission result."""
+    behavior: Literal["allow"] = "allow"
+    updatedInput: dict[str, Any] | None = None
+    updatedPermissions: list[PermissionUpdate] | None = None
+
+@dataclass
+class PermissionResultDeny:
+    """Deny permission result."""
+    behavior: Literal["deny"] = "deny" 
+    message: str = ""
+    interrupt: bool = False
+
+PermissionResult = PermissionResultAllow | PermissionResultDeny
+
+CanUseTool = Callable[
+    [str, dict[str, Any], ToolPermissionContext],
+    Awaitable[PermissionResult]
+]
+
+
+# Hook callback types
+@dataclass
+class HookContext:
+    """Context information for hook callbacks."""
+
+    signal: Any | None = None  # Future: abort signal support
+
+
+HookCallback = Callable[
+    [dict[str, Any], str | None, HookContext],  # input, tool_use_id, context
+    Awaitable[dict[str, Any]]  # response data
+]
+
+
+# Hook matcher configuration
+@dataclass
+class HookMatcher:
+    """Hook matcher configuration."""
+
+    matcher: dict[str, Any] | None = None  # Matcher criteria
+    hooks: list[HookCallback] = field(default_factory=list)  # Callbacks to invoke
+
+
 # MCP Server config
 class McpStdioServerConfig(TypedDict):
     """MCP stdio server configuration."""
@@ -155,6 +240,12 @@ class ClaudeCodeOptions:
         default_factory=dict
     )  # Pass arbitrary CLI flags
 
+    # Tool permission callback
+    can_use_tool: CanUseTool | None = None
+
+    # Hook configurations
+    hooks: dict[str, list[HookMatcher]] | None = None
+
 
 # SDK Control Protocol
 class SDKControlInterruptRequest(TypedDict):
@@ -169,7 +260,6 @@ class SDKControlPermissionRequest(TypedDict):
     permission_suggestions: list[Any] | None
     blocked_path: str | None
 
-
 class SDKControlInitializeRequest(TypedDict):
     subtype: Literal["initialize"]
     # TODO: Use HookEvent names as the key.

tests/test_tool_callbacks.py

@@ -0,0 +1,316 @@
+"""Tests for tool permission callbacks and hook callbacks."""
+
+import pytest
+
+from claude_code_sdk import (
+    ClaudeCodeOptions,
+    HookContext,
+    HookMatcher,
+    PermissionResultAllow,
+    PermissionResultDeny,
+    ToolPermissionContext,
+)
+from claude_code_sdk._internal.query import Query
+from claude_code_sdk._internal.transport import Transport
+
+
+class MockTransport(Transport):
+    """Mock transport for testing."""
+
+    def __init__(self):
+        self.written_messages = []
+        self.messages_to_read = []
+        self._connected = False
+
+    async def connect(self) -> None:
+        self._connected = True
+
+    async def close(self) -> None:
+        self._connected = False
+
+    async def write(self, data: str) -> None:
+        self.written_messages.append(data)
+
+    async def end_input(self) -> None:
+        pass
+
+    def read_messages(self):
+        async def _read():
+            for msg in self.messages_to_read:
+                yield msg
+        return _read()
+
+    def is_ready(self) -> bool:
+        return self._connected
+
+
+class TestToolPermissionCallbacks:
+    """Test tool permission callback functionality."""
+
+    @pytest.mark.asyncio
+    async def test_permission_callback_allow(self):
+        """Test callback that allows tool execution."""
+        callback_invoked = False
+
+        async def allow_callback(
+            tool_name: str,
+            input_data: dict,
+            context: ToolPermissionContext
+        ) -> PermissionResultAllow:
+            nonlocal callback_invoked
+            callback_invoked = True
+            assert tool_name == "TestTool"
+            assert input_data == {"param": "value"}
+            return PermissionResultAllow()
+
+        transport = MockTransport()
+        query = Query(
+            transport=transport,
+            is_streaming_mode=True,
+            can_use_tool=allow_callback,
+            hooks=None
+        )
+
+        # Simulate control request
+        request = {
+            "type": "control_request",
+            "request_id": "test-1",
+            "request": {
+                "subtype": "can_use_tool",
+                "tool_name": "TestTool",
+                "input": {"param": "value"},
+                "permission_suggestions": []
+            }
+        }
+
+        await query._handle_control_request(request)
+
+        # Check callback was invoked
+        assert callback_invoked
+
+        # Check response was sent
+        assert len(transport.written_messages) == 1
+        response = transport.written_messages[0]
+        assert '"allow": true' in response
+
+    @pytest.mark.asyncio
+    async def test_permission_callback_deny(self):
+        """Test callback that denies tool execution."""
+        async def deny_callback(
+            tool_name: str,
+            input_data: dict,
+            context: ToolPermissionContext
+        ) -> PermissionResultDeny:
+            return PermissionResultDeny(
+                message="Security policy violation"
+            )
+
+        transport = MockTransport()
+        query = Query(
+            transport=transport,
+            is_streaming_mode=True,
+            can_use_tool=deny_callback,
+            hooks=None
+        )
+
+        request = {
+            "type": "control_request",
+            "request_id": "test-2",
+            "request": {
+                "subtype": "can_use_tool",
+                "tool_name": "DangerousTool",
+                "input": {"command": "rm -rf /"},
+                "permission_suggestions": ["deny"]
+            }
+        }
+
+        await query._handle_control_request(request)
+
+        # Check response
+        assert len(transport.written_messages) == 1
+        response = transport.written_messages[0]
+        assert '"allow": false' in response
+        assert '"reason": "Security policy violation"' in response
+
+    @pytest.mark.asyncio
+    async def test_permission_callback_input_modification(self):
+        """Test callback that modifies tool input."""
+        async def modify_callback(
+            tool_name: str,
+            input_data: dict,
+            context: ToolPermissionContext
+        ) -> PermissionResultAllow:
+            # Modify the input to add safety flag
+            modified_input = input_data.copy()
+            modified_input["safe_mode"] = True
+            return PermissionResultAllow(
+                updatedInput=modified_input
+            )
+
+        transport = MockTransport()
+        query = Query(
+            transport=transport,
+            is_streaming_mode=True,
+            can_use_tool=modify_callback,
+            hooks=None
+        )
+
+        request = {
+            "type": "control_request",
+            "request_id": "test-3",
+            "request": {
+                "subtype": "can_use_tool",
+                "tool_name": "WriteTool",
+                "input": {"file_path": "/etc/passwd"},
+                "permission_suggestions": []
+            }
+        }
+
+        await query._handle_control_request(request)
+
+        # Check response includes modified input
+        assert len(transport.written_messages) == 1
+        response = transport.written_messages[0]
+        assert '"allow": true' in response
+        assert '"safe_mode": true' in response
+
+    @pytest.mark.asyncio
+    async def test_callback_exception_handling(self):
+        """Test that callback exceptions are properly handled."""
+        async def error_callback(
+            tool_name: str,
+            input_data: dict,
+            context: ToolPermissionContext
+        ) -> PermissionResultAllow:
+            raise ValueError("Callback error")
+
+        transport = MockTransport()
+        query = Query(
+            transport=transport,
+            is_streaming_mode=True,
+            can_use_tool=error_callback,
+            hooks=None
+        )
+
+        request = {
+            "type": "control_request",
+            "request_id": "test-5",
+            "request": {
+                "subtype": "can_use_tool",
+                "tool_name": "TestTool",
+                "input": {},
+                "permission_suggestions": []
+            }
+        }
+
+        await query._handle_control_request(request)
+
+        # Check error response was sent
+        assert len(transport.written_messages) == 1
+        response = transport.written_messages[0]
+        assert '"subtype": "error"' in response
+        assert "Callback error" in response
+
+
+class TestHookCallbacks:
+    """Test hook callback functionality."""
+
+    @pytest.mark.asyncio
+    async def test_hook_execution(self):
+        """Test that hooks are called at appropriate times."""
+        hook_calls = []
+
+        async def test_hook(
+            input_data: dict,
+            tool_use_id: str | None,
+            context: HookContext
+        ) -> dict:
+            hook_calls.append({
+                "input": input_data,
+                "tool_use_id": tool_use_id
+            })
+            return {"processed": True}
+
+        transport = MockTransport()
+
+        # Create hooks configuration
+        hooks = {
+            "tool_use_start": [
+                {
+                    "matcher": {"tool": "TestTool"},
+                    "hooks": [test_hook]
+                }
+            ]
+        }
+
+        query = Query(
+            transport=transport,
+            is_streaming_mode=True,
+            can_use_tool=None,
+            hooks=hooks
+        )
+
+        # Manually register the hook callback to avoid needing the full initialize flow
+        callback_id = "test_hook_0"
+        query.hook_callbacks[callback_id] = test_hook
+
+        # Simulate hook callback request
+        request = {
+            "type": "control_request",
+            "request_id": "test-hook-1",
+            "request": {
+                "subtype": "hook_callback",
+                "callback_id": callback_id,
+                "input": {"test": "data"},
+                "tool_use_id": "tool-123"
+            }
+        }
+
+        await query._handle_control_request(request)
+
+        # Check hook was called
+        assert len(hook_calls) == 1
+        assert hook_calls[0]["input"] == {"test": "data"}
+        assert hook_calls[0]["tool_use_id"] == "tool-123"
+
+        # Check response
+        assert len(transport.written_messages) > 0
+        last_response = transport.written_messages[-1]
+        assert '"processed": true' in last_response
+
+
+class TestClaudeCodeOptionsIntegration:
+    """Test that callbacks work through ClaudeCodeOptions."""
+
+    def test_options_with_callbacks(self):
+        """Test creating options with callbacks."""
+        async def my_callback(
+            tool_name: str,
+            input_data: dict,
+            context: ToolPermissionContext
+        ) -> PermissionResultAllow:
+            return PermissionResultAllow()
+
+        async def my_hook(
+            input_data: dict,
+            tool_use_id: str | None,
+            context: HookContext
+        ) -> dict:
+            return {}
+
+        options = ClaudeCodeOptions(
+            can_use_tool=my_callback,
+            hooks={
+                "tool_use_start": [
+                    HookMatcher(
+                        matcher={"tool": "Bash"},
+                        hooks=[my_hook]
+                    )
+                ]
+            }
+        )
+
+        assert options.can_use_tool == my_callback
+        assert "tool_use_start" in options.hooks
+        assert len(options.hooks["tool_use_start"]) == 1
+        assert options.hooks["tool_use_start"][0].hooks[0] == my_hook