Function Calling Patterns

Complete guide to implementing function calling (tool use) with Gemini API.

Basic Pattern

Define function declarations
Send request with tools
Check if model wants to call functions
Execute functions
Send results back to model
Get final response

Function Declaration Schema

{
  name: string,                    // Function name (no spaces)
  description: string,             // What the function does
  parametersJsonSchema: {          // Subset of OpenAPI schema
    type: 'object',
    properties: {
      [paramName]: {
        type: string,              // 'string' | 'number' | 'boolean' | 'array' | 'object'
        description: string,       // Parameter description
        enum?: string[]            // Optional: allowed values
      }
    },
    required: string[]            // Required parameter names
  }
}

Calling Modes

AUTO (default): Model decides when to call
ANY: Force at least one function call
NONE: Disable function calling

Parallel vs Compositional

Parallel: Independent functions run simultaneously Compositional: Sequential dependencies (A → B → C)

Gemini automatically detects which pattern to use.

Official Docs

https://ai.google.dev/gemini-api/docs/function-calling

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