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AI Function Calling Schema

Generate strict JSON schemas for OpenAI Function Calling, Structured Outputs, and Anthropic Claude Tools.

Runs in your browser. Nothing you add is uploaded.

What the AI Function Calling Schema does

Function calling and tool use allow AI models to interact with databases, web APIs, and local code by emitting structured JSON arguments. Building compliant schemas manually is tedious and error-prone. This tool builds strict OpenAI Structured Outputs (additionalProperties: false) and Anthropic Claude Tool schemas with instant TypeScript interface export.

How to build AI function calling schemas

  1. Enter the tool name in snake_case (e.g. get_current_weather) and provide a clear description.
  2. Add parameters with their name, type (string, number, boolean, array, object), and description.
  3. Specify optional enum choices (e.g. celsius, fahrenheit) for restricted parameter options.
  4. Toggle OpenAI Strict Mode to enforce 'additionalProperties: false' for guaranteed schema compliance.
  5. Switch between OpenAI Tools, Anthropic Claude, and TypeScript tabs to copy or download your schema.

The AI Function Calling Schema runs entirely in your browser — nothing you enter is uploaded, stored, or logged.

When to use it

OpenAI Structured Outputs & Function Calling

Build reliable tool definitions for gpt-4o and gpt-4o-mini that guarantee JSON payloads match your exact API parameters 100% of the time.

Anthropic Claude Tool Use

Generate clean input_schema definitions for Claude 3.5 Sonnet to invoke external search engines, calculators, and databases.

Full-Stack TypeScript End-to-End Typing

Export matching TypeScript interfaces to strongly type function call handler arguments on your backend server.

Good to know

  • Parameter descriptions are critical: the model reads them to determine what values to extract and format.
  • In OpenAI Strict Mode, every single property defined in the schema must also be listed in the required array.
  • Use enum constraints whenever a parameter accepts a fixed set of choices to prevent invalid inputs.

Frequently asked questions

What are OpenAI Structured Outputs?

Structured Outputs ensure the model's generated response strictly matches your supplied JSON Schema 100% of the time. It requires 'strict: true', 'additionalProperties: false', and all properties listed in 'required'.

How do Anthropic Claude Tool definitions differ from OpenAI?

Anthropic uses an 'input_schema' object at the top level of each tool, whereas OpenAI wraps function definitions inside a 'function' property within a 'type: "function"' array object.

What does 'additionalProperties: false' mean in JSON Schema?

It tells the schema validator (and the model's constrained decoding engine) that no undeclared keys are permitted in the generated JSON object, ensuring strict data hygiene.

How do tools differ from standard JSON mode?

Standard JSON mode only ensures valid JSON syntax. Function calling and tool definitions constrain the model to output a specific schema chosen dynamically from multiple available tools.

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