JSON Schema Builder
Define fields visually and get a valid JSON Schema — plus ready-to-paste OpenAI function-calling and Anthropic tool formats — for LLM structured outputs. No AI call, runs in your browser.
{
"type": "object",
"properties": {}
}About JSON Schema Builder
Modern LLMs can return structured JSON if you give them a schema — via OpenAI's function calling / structured outputs or Anthropic's tool use. Writing that schema by hand is fiddly. This builder lets you define each field's name, type, description, and whether it's required, then emits a valid JSON Schema plus the exact wrapper each provider expects. It's a pure generator — no model is called, so it's instant and free.
Frequently asked questions
What formats does it output?+
A plain JSON Schema object, an OpenAI function/tool definition (with the schema under parameters), and an Anthropic tool definition (with the schema under input_schema).
Why use structured outputs?+
A schema forces the model to return predictable, parseable JSON with the right keys and types, so you can use its output directly in code without brittle string parsing.
Does it support nested objects?+
This builder focuses on flat schemas with scalars, enums, and simple arrays — which covers most function-calling needs. For deep nesting, use the output as a starting point.