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Zhongwei Li
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skills/langgraph-master/04_tool_integration_tool_node.md
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skills/langgraph-master/04_tool_integration_tool_node.md
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# Tool Node
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Implementation of nodes that execute tools.
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## ToolNode (Built-in)
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The simplest approach:
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```python
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from langgraph.prebuilt import ToolNode
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tools = [search_tool, calculator_tool]
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tool_node = ToolNode(tools)
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# Add to graph
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builder.add_node("tools", tool_node)
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```
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## How It Works
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ToolNode:
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1. Extracts `tool_calls` from the last message
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2. Executes each tool
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3. Returns results as `ToolMessage`
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```python
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# Input
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{
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"messages": [
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AIMessage(tool_calls=[
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{"name": "search", "args": {"query": "weather"}, "id": "1"}
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])
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]
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}
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# ToolNode execution
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# Output
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{
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"messages": [
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ToolMessage(
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content="Sunny, 25°C",
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tool_call_id="1"
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)
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]
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}
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```
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## Custom Tool Node
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For finer control:
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```python
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def custom_tool_node(state: MessagesState):
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"""Custom tool node"""
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last_message = state["messages"][-1]
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tool_results = []
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for tool_call in last_message.tool_calls:
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# Find the tool
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tool = tool_map.get(tool_call["name"])
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if not tool:
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result = f"Tool {tool_call['name']} not found"
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else:
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try:
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# Execute the tool
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result = tool.invoke(tool_call["args"])
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except Exception as e:
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result = f"Error: {str(e)}"
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# Create ToolMessage
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tool_results.append(
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ToolMessage(
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content=str(result),
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tool_call_id=tool_call["id"]
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)
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)
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return {"messages": tool_results}
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```
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## Error Handling
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### Basic Error Handling
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```python
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def robust_tool_node(state: MessagesState):
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"""Tool node with error handling"""
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last_message = state["messages"][-1]
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tool_results = []
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for tool_call in last_message.tool_calls:
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try:
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tool = tool_map[tool_call["name"]]
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result = tool.invoke(tool_call["args"])
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tool_results.append(
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ToolMessage(
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content=str(result),
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tool_call_id=tool_call["id"]
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)
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)
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except KeyError:
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# Tool not found
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tool_results.append(
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ToolMessage(
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content=f"Error: Tool '{tool_call['name']}' not found",
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tool_call_id=tool_call["id"]
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)
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)
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except Exception as e:
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# Execution error
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tool_results.append(
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ToolMessage(
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content=f"Error executing tool: {str(e)}",
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tool_call_id=tool_call["id"]
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)
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)
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return {"messages": tool_results}
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```
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### Retry Logic
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```python
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import time
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def tool_node_with_retry(state: MessagesState, max_retries: int = 3):
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"""Tool node with retry"""
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last_message = state["messages"][-1]
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tool_results = []
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for tool_call in last_message.tool_calls:
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tool = tool_map[tool_call["name"]]
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retry_count = 0
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while retry_count < max_retries:
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try:
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result = tool.invoke(tool_call["args"])
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tool_results.append(
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ToolMessage(
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content=str(result),
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tool_call_id=tool_call["id"]
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)
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)
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break
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except TransientError as e:
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retry_count += 1
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if retry_count >= max_retries:
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tool_results.append(
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ToolMessage(
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content=f"Failed after {max_retries} retries: {str(e)}",
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tool_call_id=tool_call["id"]
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)
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)
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else:
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time.sleep(2 ** retry_count) # Exponential backoff
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except Exception as e:
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# Non-retryable error
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tool_results.append(
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ToolMessage(
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content=f"Error: {str(e)}",
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tool_call_id=tool_call["id"]
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)
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)
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break
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return {"messages": tool_results}
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```
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## Conditional Tool Execution
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```python
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def conditional_tool_node(state: MessagesState, *, store):
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"""Tool node with permission checking"""
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user_id = state.get("user_id")
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user = store.get(("users", user_id), "profile")
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last_message = state["messages"][-1]
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tool_results = []
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for tool_call in last_message.tool_calls:
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tool = tool_map[tool_call["name"]]
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# Permission check
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if not has_permission(user, tool.name):
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tool_results.append(
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ToolMessage(
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content=f"Permission denied for tool '{tool.name}'",
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tool_call_id=tool_call["id"]
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)
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)
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continue
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# Execute
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result = tool.invoke(tool_call["args"])
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tool_results.append(
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ToolMessage(
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content=str(result),
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tool_call_id=tool_call["id"]
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)
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)
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return {"messages": tool_results}
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```
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## Logging Tool Execution
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```python
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import logging
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logger = logging.getLogger(__name__)
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def logged_tool_node(state: MessagesState):
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"""Tool node with logging"""
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last_message = state["messages"][-1]
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tool_results = []
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for tool_call in last_message.tool_calls:
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tool = tool_map[tool_call["name"]]
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logger.info(
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f"Executing tool: {tool.name}",
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extra={
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"tool": tool.name,
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"args": tool_call["args"],
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"call_id": tool_call["id"]
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}
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)
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try:
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start = time.time()
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result = tool.invoke(tool_call["args"])
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duration = time.time() - start
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logger.info(
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f"Tool completed: {tool.name}",
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extra={
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"tool": tool.name,
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"duration": duration,
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"success": True
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}
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)
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tool_results.append(
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ToolMessage(
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content=str(result),
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tool_call_id=tool_call["id"]
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)
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)
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except Exception as e:
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logger.error(
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f"Tool failed: {tool.name}",
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extra={
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"tool": tool.name,
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"error": str(e)
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},
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exc_info=True
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)
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tool_results.append(
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ToolMessage(
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content=f"Error: {str(e)}",
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tool_call_id=tool_call["id"]
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)
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)
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return {"messages": tool_results}
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```
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## Parallel Tool Execution
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```python
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from concurrent.futures import ThreadPoolExecutor
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def parallel_tool_node(state: MessagesState):
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"""Execute tools in parallel"""
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last_message = state["messages"][-1]
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def execute_tool(tool_call):
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tool = tool_map[tool_call["name"]]
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try:
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result = tool.invoke(tool_call["args"])
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return ToolMessage(
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content=str(result),
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tool_call_id=tool_call["id"]
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)
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except Exception as e:
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return ToolMessage(
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content=f"Error: {str(e)}",
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tool_call_id=tool_call["id"]
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)
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with ThreadPoolExecutor(max_workers=5) as executor:
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tool_results = list(executor.map(
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execute_tool,
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last_message.tool_calls
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))
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return {"messages": tool_results}
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```
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## Summary
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ToolNode executes tools and returns results as ToolMessage. You can add error handling, permission checks, logging, and more.
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## Related Pages
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- [04_tool_integration_tool_definition.md](04_tool_integration_tool_definition.md) - Tool definition
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- [04_tool_integration_command_api.md](04_tool_integration_command_api.md) - Integration with Command API
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- [05_advanced_features_human_in_the_loop.md](05_advanced_features_human_in_the_loop.md) - Combining with approval flows
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