Azure Agentic AI- unable to register and run custom function call?

Question

Hello,

i am trying to build a agenti ai using custom call as per the azure document.

i followed the exact code in my code base, however when running the agent, i am getting below error.

https://learn.microsoft.com/en-us/azure/ai-services/agents/how-to/tools/function-calling?tabs=python&pivots=code-example

```
import json
import datetime
from typing import Any, Callable, Set, Dict, List, Optional

def fetch_weather(location: str) -> str:
    """
    Fetches the weather information for the specified location.

    :param location (str): The location to fetch weather for.
    :return: Weather information as a JSON string.
    :rtype: str
    """
    # In a real-world scenario, you'd integrate with a weather API.
    # Here, we'll mock the response.
    mock_weather_data = {"New York": "Sunny, 25°C", "London": "Cloudy, 18°C", "Tokyo": "Rainy, 22°C"}
    weather = mock_weather_data.get(location, "Weather data not available for this location.")
    weather_json = json.dumps({"weather": weather})
    return weather_json

# Statically defined user functions for fast reference
user_functions: Set[Callable[..., Any]] = {
    fetch_weather,
}

functions = FunctionTool(user_functions)
## Create a function tool to bind the function
toolset = ToolSet()
# 
toolset.add(functions)

ERROR:root:Error executing function 'fetch_weather': Function 'fetch_weather' not found.
WARNING:root:Tool outputs contain errors - retrying
ERROR:root:Error executing function 'fetch_weather': Function 'fetch_weather' not found.
```

Answer 1

Hello Umesh,

You're close, but the issue stems from how the function is registered and used in Azure Agentic AI's FunctionTool

ERROR:root:Error executing function 'fetch_weather': Function 'fetch_weather' not found.

This error means the function name is not being correctly matched or not registered in the internal function registry that FunctionTool uses.

You must ensure the function is wrapped correctly and registered with its name string so the agent can look it up.

Import the required Azure classes

Make sure you're importing the right classes from azure.ai.services.agents.tools.

from azure.ai.services.agents.tools import FunctionTool, ToolSet

Use a FunctionTool with proper function name mapping

Update your code like this:
import json

from azure.ai.services.agents.tools import FunctionTool, ToolSet

Step 1: Define the function

def fetch_weather(location: str) -> str:

mock_weather_data = {

    "New York": "Sunny, 25°C",

    "London": "Cloudy, 18°C",

    "Tokyo": "Rainy, 22°C"

}

weather = mock_weather_data.get(location, "Weather data not available for this location.")

return json.dumps({"weather": weather})

Step 2: Create a FunctionTool instance

weather_tool = FunctionTool(fetch_weather)

Step 3: Create a ToolSet and register the tool

toolset = ToolSet()

toolset. Add(weather_tool)

This ensures:

The function fetch_weather is registered by its actual name.

• FunctionTool wraps the function correctly for the Azure Agent runtime.

Problem in Your Current Code

user_functions: Set[Callable[..., Any]] = {

fetch_weather,

}

functions = FunctionTool(user_functions)

This incorrectly passes a set of functions instead of individual ones. FunctionTool() expects one function at a time, not a set.

Make sure the tool is referenced with the exact name the function defines (fetch_weather in this case) — Agentic AI resolves the name via introspection.

Best Regards,

Jerald Felix

Answer 2

Hello Umesh Narayanan AV,

Welcome to the Microsoft Q&A and thank you for posting your questions here.

I understand that your Azure Agentic AI- unable to register and run custom function call.

For permanent solution:

1. Add a JSON schema to ensure compatibility (required for some SDK versions):

      from azure.ai.services.agents.tools import FunctionTool, ToolSet
      def fetch_weather(location: str) -> str:
          mock_weather_data = {"New York": "Sunny, 25°C", "London": "Cloudy, 18°C", "Tokyo": "Rainy, 22°C"}
          weather = mock_weather_data.get(location, "Weather data not available.")
          return json.dumps({"weather": weather})
       Define the function schema explicitly (required for some SDK versions)
      fetch_weather_schema = {
          "name": "fetch_weather",
          "description": "Fetches weather data for a location.",
          "parameters": {
              "type": "object",
              "properties": {
                  "location": {"type": "string", "description": "The city name."}
              },
              "required": ["location"]
          }
      }
   

   You can use official Microsoft Docs - https://learn.microsoft.com/en-us/azure/ai-services/agents/how-to/tools/function-callingdefining-function-schemas
2. Use FunctionTool with the schema and add it to the ToolSet:

      weather_tool = FunctionTool(
          func=fetch_weather,
          name="fetch_weather",   Explicitly set the name (avoids introspection issues)
          schema=fetch_weather_schema   Required for SDKs with strict validation
      )
      toolset = ToolSet()
      toolset.add(weather_tool) 
   

   https://learn.microsoft.com/en-us/python/api/azure-ai-agents/azure.ai.agents.tools.functiontool
3. To initialize the Agent with the ToolSet, make sure the agent uses the registered tools:

      from azure.ai.services.agents import AzureAgent
      agent = AzureAgent(
          tools=toolset,   Pass the ToolSet here
           Include other required parameters (e.g., API key, endpoint)
      ) 
   

   Read more on Azure Agent Initialization - https://learn.microsoft.com/en-us/azure/ai-services/agents/how-to/create-agent
4. Check compatibility with the latest SDK:

      pip install --upgrade azure-ai-agents
   

   https://learn.microsoft.com/en-us/azure/ai-services/agents/get-started
5. If the error persists:
   • Ensure name="fetch_weather" matches the function’s actual name.
   • Print registered tools with print(toolset.list_tools()).
   • Look for initialization errors or schema mismatches.

I hope this is helpful! Do not hesitate to let me know if you have any other questions or clarifications.

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