ToolFunctionException
langchain.tools.base.ToolFunctionException
Stack trace
Traceback (most recent call last):
File "app.py", line 42, in run_tool
result = tool_function(*args)
File "tools.py", line 10, in tool_function
raise ValueError("Invalid input")
langchain.tools.base.ToolFunctionException: Exception in tool function: Invalid input Why it happens
When the LLM triggers a tool function during function-calling, any exception raised inside that function must be caught and handled properly. If the tool function raises an error without a try/except block, the exception propagates uncaught, causing this error and crashing the app.
Detection
Monitor logs for uncaught exceptions in tool functions and wrap tool calls in try/except blocks to catch and log errors before they crash the application.
Causes & fixes
Tool function raises an exception without internal error handling
Add try/except blocks inside the tool function to catch and handle expected errors gracefully.
Calling code invoking the tool function does not catch exceptions
Wrap calls to tool functions in try/except blocks to catch exceptions and handle or log them appropriately.
Unexpected input or edge cases cause the tool function to fail
Validate inputs before processing and add defensive programming to handle edge cases inside the tool function.
Code: broken vs fixed
def tool_function(data):
# This will raise an exception if data is invalid
return 10 / data # triggers ZeroDivisionError if data=0
result = tool_function(0) # uncaught exception here
print(result)import os
def tool_function(data):
try:
return 10 / data # may raise ZeroDivisionError
except ZeroDivisionError:
return "Error: division by zero"
result = tool_function(0) # handled safely
print(result) # prints error message
# API keys or environment variables can be set here if needed
os.environ["API_KEY"] = os.getenv("API_KEY")Workaround
Temporarily wrap all tool function calls in try/except blocks at the call site to catch exceptions and log errors, avoiding crashes until the tool functions are fixed.
Prevention
Design tool functions with robust input validation and internal error handling, and always wrap calls in try/except to ensure exceptions are caught and managed gracefully.