API Documentation Generator
Build OpenAPI 3.0 / Swagger YAML documentation visually. Define endpoints, parameters, request bodies, responses, and schemas using a form.
About This Tool
The API Documentation Generator is a free browser-based tool that helps you create OpenAPI 3.0 (formerly Swagger) YAML documentation through a visual form instead of writing YAML by hand. Fill in your API information, define servers, add endpoints with HTTP methods (GET, POST, PUT, DELETE, PATCH), configure parameters (query, path, header, cookie), request bodies, responses with status codes, and reusable component schemas. The tool generates valid OpenAPI 3.0.3 YAML in real time as you type.
The builder supports all the core sections of an OpenAPI specification: info (title, version, description, contact, license, terms of service), servers (multiple server URLs with descriptions), paths (unlimited endpoints with full operation details), and components/schemas (reusable data models with typed properties and required field markers). Each endpoint can have multiple parameters across all four OpenAPI locations, a request body with content type selection, and multiple response definitions with schema references.
If you need to validate your YAML syntax, try the YAML Formatter for formatting and error detection. For converting between JSON and YAML formats, the JSON to YAML Converter handles bidirectional conversion. You can also use the JSON Schema Generator to create schemas from sample data and paste them into your API documentation.
All processing runs entirely in your browser. No API definitions, endpoint details, or schema information is ever sent to any server. This tool is safe to use with internal API specifications and proprietary endpoint designs.
How to Use
- Fill in the API Info section with your API title, version, and description. Optionally add contact information and license details.
- Add one or more Servers with their base URLs and descriptions (e.g., production, staging, development).
- Click Add Endpoint to create API endpoints. Select an HTTP method (GET, POST, PUT, DELETE, PATCH) and enter the path (e.g.,
/users/{id}). - For each endpoint, add Parameters (query, path, header, or cookie) with their name, type, and required status. Add a Request Body for POST/PUT/PATCH methods with content type and schema reference.
- Define Responses for each endpoint with status codes (200, 201, 400, 404, etc.), descriptions, and optional schema references.
- Expand the Schemas / Components section to define reusable data models with typed properties. Reference these schemas in your request bodies and responses.
- Review the generated OpenAPI YAML on the right panel. Click Copy or press Ctrl+Shift+C to copy, or click Download to save as
openapi.yaml.
Popular API Documentation Examples
FAQ
What version of OpenAPI does this generate?
This tool generates OpenAPI Specification version 3.0.3. This is the most widely supported version and is compatible with tools like Swagger UI, Redoc, Postman, and most API gateways. OpenAPI 3.0 is the successor to Swagger 2.0 and adds support for multiple servers, request bodies as first-class objects, and a more flexible component model.
Can I use $ref references between schemas?
Yes. When you define schemas in the Components section, you can reference them in request bodies and responses by entering the schema name. The tool automatically creates proper $ref paths (e.g., #/components/schemas/User). This keeps your API documentation DRY and maintainable.
How do I document path parameters like /users/{id}?
Enter the path with curly braces for variables (e.g., /users/{id}), then add a parameter with the same name (id) and set its location to 'path'. Mark it as required since path parameters are always required in OpenAPI. The tool will include the parameter definition in the generated YAML.
Can I define authentication/security schemes?
The current version focuses on core API structure (paths, parameters, schemas, responses). For security schemes like OAuth2, API keys, or Bearer tokens, you can add them manually to the generated YAML. The tool generates a valid base that you can extend with additional OpenAPI sections.
Is the generated YAML valid OpenAPI?
Yes. The tool generates syntactically valid OpenAPI 3.0.3 YAML that follows the specification structure. The output includes proper YAML formatting, correct $ref paths for schema references, and all required fields. You can validate the output with any OpenAPI validator like Swagger Editor or Spectral.
Is my data safe?
Yes. All documentation generation runs entirely in your browser using JavaScript. No API definitions, endpoint details, schema structures, or any other data is ever sent to any server. You can verify this by checking the Network tab in your browser's developer tools while using the tool.
Can I import an existing OpenAPI file?
The current version is designed for building new API documentation from scratch. To edit existing OpenAPI files, you can use the generated YAML as a starting point and modify the output directly. The YAML Formatter tool can help you format and validate existing YAML files.
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