OpenAPI Mock Generator

An OpenAPI mock generator reads your OpenAPI/Swagger specification (YAML or JSON) and automatically creates realistic sample JSON responses for each endpoint. This lets frontend developers build against a realistic API contract without waiting for the backend to be complete.

This tool supports OpenAPI 3.0.x and 3.1.x specifications. Swagger 2.0 format has limited support — convert to OpenAPI 3 first using the Swagger Editor or swagger2openapi for best results.

Mock values are derived from the schema type and format fields. Strings become example strings or use the 'example' field if provided, integers generate realistic numbers, booleans alternate true/false, dates use ISO 8601 format, emails look like [email protected], and UUIDs are generated in standard format. Arrays generate 2-3 example items.

Yes. Copy the generated mock JSON and use it as fixture data in your unit tests, Postman mock servers, or local development stubs. The mock responses match the schema shape your API client expects, so you can validate your serialization and deserialization logic without hitting a live server.

YAML is whitespace-sensitive. Common issues: tabs instead of spaces (YAML requires spaces), incorrect indentation levels, missing colons after keys, or unquoted strings containing special characters like : or #. Paste your spec into a YAML validator first to find syntax errors.

No. All parsing and mock generation runs entirely in your browser using JavaScript. Your API specification — which may contain endpoint paths, schema definitions, and security schemes — never leaves your machine.