Function Call Generator

An AI function call generator converts JSON examples or JSON Schema definitions into the specific function/tool definition formats required by major AI providers — OpenAI, Anthropic (Claude), and Google Gemini. Instead of manually writing these verbose JSON structures, you provide an example payload and the tool infers the schema, types, and structure automatically.

Function calling (also called tool use) is how AI models interact with external systems. When you want an LLM to call an API, query a database, or trigger an action, you define a function schema that tells the model what parameters are available, their types, and which are required. Each AI provider uses a slightly different format for these definitions — OpenAI uses functions or tools arrays, Anthropic uses input_schema, and Gemini uses uppercase type names.

Our generator eliminates the tedious, error-prone process of writing these definitions by hand. Paste a JSON example (like a sample API request body), and the tool infers property types, generates schemas for all three major providers, and lets you customize descriptions, required fields, and parameter names. All processing happens in your browser — your function definitions and API structures are never sent anywhere.

1. Choose your input mode — Select "From JSON Example" to paste a sample JSON object, or "From JSON Schema" to paste an existing JSON Schema definition.
2. Paste your JSON — Enter a JSON object representing your function's parameters. For example: {"location": "San Francisco", "unit": "celsius"}. Or try one of the built-in presets (weather, search, email, task).
3. Click "Generate Function Definition" — The tool infers types from your JSON values (string, number, boolean, array, object) and generates function definitions for all providers.
4. Customize the schema — Set the function name and description. For each parameter, add a description, toggle required/optional, or remove unnecessary fields.
5. Copy the output — Switch between OpenAI Function, OpenAI Tool, Anthropic, and Gemini tabs to copy the exact format you need.

• Multi-provider output — Generates function definitions for OpenAI (function and tool formats), Anthropic Claude, and Google Gemini simultaneously.
• Automatic type inference — Infers JSON Schema types from your example values: strings, integers, numbers, booleans, arrays (with item types), and nested objects.
• JSON Schema input — Already have a JSON Schema? Paste it directly and the tool converts it to all provider formats without re-inferring types.
• Built-in presets — Start from common examples (weather lookup, product search, send email, create task) and customize from there.
• Parameter editing — Add descriptions to each parameter, toggle required/optional status, and remove parameters — all reflected live in the output.
• Validation — Function name validation ensures your names follow the required format (alphanumeric and underscores only).
• 100% client-side — Your JSON and function definitions never leave your browser. No API calls, no server processing.

• Building AI agent tools — Quickly define function schemas for AI agents that need to call APIs, query databases, or trigger workflows.
• Migrating between AI providers — Convert function definitions from OpenAI format to Anthropic or Gemini format (or vice versa) when switching providers.
• Prototyping AI integrations — Rapidly generate function definitions from example API request bodies to prototype AI-powered features.
• Documentation and testing — Generate properly structured function schemas for API documentation or testing AI tool-use capabilities.
• Learning function calling — Understand the different function definition formats across providers by seeing the same schema in multiple output formats.