JSON Schema Builder
Visually build a JSON Schema for tool use and structured outputs. Add fields, mark them required, nest objects one level deep, and copy the result as a plain JSON Schema, a Claude tool definition, or an OpenAI function definition.
Names should only use letters, numbers, underscores, and hyphens.
Fields
How to use the output: the JSON Schema tab is the raw schema, usable anywhere JSON Schema is accepted (including structured outputs). The Claude tool tab wraps it as
{"name", "description", "input_schema"} for the Messages API tools array; add "strict": true at the top level of the tool for guaranteed schema-valid inputs. The OpenAI function tab wraps it as {"type": "function", "function": {...}} for the Chat Completions tools array (check OpenAI docs for the latest shape). The builder sets "additionalProperties": false and fills the required array for you, both of which strict modes expect. Field descriptions matter: the model uses them to decide what to pass, so write them like documentation.