OpenAI Function / Tool Schema Builder

Build OpenAI function-calling (tool-use) JSON schemas visually. Add parameters with types, descriptions, required flags, enum constraints. Output is ready to pass to chat.completions.create({tools: [...]}). Compatible with strict mode (strict: true) — emits the required additionalProperties: false.

How to use the OpenAI Function / Tool Schema Builder

Name the function, write a description, add parameters one at a time. For each parameter set type, description, whether required, optional enum constraints. The generated schema follows OpenAI's function-calling spec and works with both legacy function_call and modern tools array.

Function-calling schemas for OpenAI

OpenAI function calling lets a model return a structured call to one of your functions instead of free text. You pass a tools array, where each tool wraps a function with a name, a description, and a parameters object in JSON Schema. The model reads those and emits arguments matching the schema, which your code then executes.

Strict mode tightens this: set strict: true and the schema must mark additionalProperties: false and list every property as required, guaranteeing the arguments conform. Hand-writing that JSON is error-prone, so this builder lets you add parameters with types, enums, and required flags and emits a valid schema — including the strict-mode constraints. For Claude's equivalent, see the Anthropic tool builder.

Common use cases

• Function calling — define a function the model can invoke with structured arguments.
• Strict structured output — emit the additionalProperties: false form strict mode requires.
• Enum constraints — restrict a parameter to a fixed set of allowed values.
• Agent tools — build one schema per capability your agent offers the model.
• Spec reference — produce a known-valid example to model your own schemas on.