What name rules does OpenAI enforce?

Function names must be 1-64 characters and contain only letters, numbers, underscores, and hyphens. Spaces and most punctuation are rejected by the API.

Do parameters have to be a JSON Schema object?

Yes. The parameters field must be a JSON Schema object with type 'object' and a properties map. Each property should declare a type; descriptions are optional but strongly recommended for better tool selection.

How deep can my schema nest?

OpenAI supports nested objects and arrays, but very deep nesting hurts reliability. This validator warns past a practical depth so the model can still fill the arguments correctly.

Is my schema sent anywhere?

No. Validation runs entirely in your browser. Nothing you paste is uploaded, stored, or logged.

OpenAI Function Schema Validator

Validate before the API rejects it

A malformed tool schema is a common, frustrating failure: the OpenAI API returns a 400, or worse, the model fills arguments badly because the schema is ambiguous. Paste your tool definition here and get an instant checklist — name format, required fields, parameter types, description quality, and nesting depth — so you catch problems before you ship.

How it works

The validator parses your JSON and runs a set of rules drawn from OpenAI’s function-calling specification. It accepts either a full tool object ({ "type": "function", "function": { … } }) or just the function definition. It checks that name is present and uses only allowed characters, that description exists and isn’t excessively long, that parameters is a proper JSON Schema object with a properties map, that each property declares a type, and that nesting stays within a practical depth.

Tips

Always describe each parameter. The model uses descriptions to decide what to put in each field; vague schemas produce vague calls.
Mark required fields explicitly in the required array — otherwise the model may omit them.
Keep it shallow. Flatter schemas with clear enums are filled far more reliably than deeply nested ones.