Function Calling

What is Function Calling?

Function calling (also called tool use) is a capability that allows language models to generate structured outputs that trigger external functions or APIs. Instead of generating text, the model outputs structured parameters for predefined functions.

How It Works

1. Define Functions

   • Name and description
   • Parameter schema
   • Expected behavior

2. User Query

   • Natural language request
   • Context about task

3. Model Decision

   • Determine if function needed
   • Select appropriate function
   • Generate parameters

4. Execution

   • Call external function
   • Return results to model

5. Response

   • Model uses results
   • Generates final answer

Function Definition Example

{
  "name": "get_weather",
  "description": "Get weather for a location",
  "parameters": {
    "type": "object",
    "properties": {
      "location": {
        "type": "string",
        "description": "City name"
      },
      "unit": {
        "type": "string",
        "enum": ["celsius", "fahrenheit"]
      }
    },
    "required": ["location"]
  }
}

Use Cases

• API integrations
• Database queries
• Calculations
• Data retrieval
• System actions

Best Practices

• Clear function descriptions
• Validate parameters
• Handle errors gracefully
• Limit available functions
• Secure function execution