Swagger / OpenAPI Generator — Spec Builder
Generate a valid OpenAPI 3.0 spec in your browser without writing YAML by hand. Define your API title, version, and server URL, then add endpoints — each with method, path, summary, tags, request body JSON, and response examples. The tool infers request and response schemas from your JSON examples and outputs a complete OpenAPI 3.0.3 spec in YAML or JSON. Download the file and use it with Swagger UI, Postman, Redoc, or any OpenAPI-compatible toolchain. Free, client-side, no signup.
How to Use Swagger / OpenAPI Generator — Spec Builder
How to Use the Swagger / OpenAPI Generator
Step 1: Fill in API Info
Enter your API title, version string (e.g. 1.0.0), server base URL, and an optional description. These populate the openapi, info, and servers sections of the spec.
Step 2: Add Endpoints
For each API endpoint:
- Select the HTTP method (GET, POST, PUT, PATCH, DELETE, etc.)
- Enter the path — use curly braces for path parameters (e.g. /users/{id})
- Enter a short summary and optional tags (comma-separated)
- For POST/PUT/PATCH endpoints, paste a JSON example of the request body
- For each response, enter the HTTP status code, a description, and optionally a JSON response body example
The generator infers the JSON Schema automatically from your examples.
Step 3: Add More Endpoints
Click "Add Endpoint" to add more paths. Each endpoint appears as a collapsible row — click the header to expand or collapse it.
Step 4: Choose Output Format
Toggle between YAML and JSON in the output panel. Both are valid OpenAPI 3.0 and work with all major tooling.
Step 5: Download and Use
Click Download to save the spec file (.yaml or .json). Use it with:
- Swagger UI / editor.swagger.io — paste YAML for instant interactive docs
- Postman — Import > File to create a collection from the spec
- Redoc or Stoplight — upload for hosted, styled documentation
- Code generators — use openapi-generator-cli to generate client SDKs
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