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OpenAPI Spec Editor

Write and validate OpenAPI 3.x specifications with a live documentation preview. Switch between YAML and JSON, use starter templates, and export your spec when ready.

Free OpenAPI Specification Editor & Validator

The OpenAPI Specification (formerly known as Swagger) is the industry standard for describing REST APIs. It provides a machine-readable format that tools can use to generate documentation, client SDKs, server stubs, and test cases. Our browser-based editor lets you write, validate, and preview OpenAPI specs without installing any software or creating an account.

What is OpenAPI?

OpenAPI is a standardized format for describing the endpoints, parameters, request bodies, responses, and authentication methods of an API. It uses either YAML or JSON to define the API structure. The current version, OpenAPI 3.0 and 3.1, improves on the older Swagger 2.0 format with better support for webhooks, links, callbacks, and JSON Schema alignment.

A well-written OpenAPI spec serves as the single source of truth for your API. It can be used to generate interactive documentation (like Swagger UI or Redoc), create client libraries in multiple languages, validate requests and responses at runtime, and even generate server-side route handlers.

How to Use This Editor

  1. Choose a format. Toggle between YAML (more human-readable) and JSON (more widely supported by tools).
  2. Start from a template. Select one of the pre-built API templates to get a working starting point, then customize it for your API.
  3. Write your spec. The editor provides syntax highlighting and real-time validation. Errors, warnings, and suggestions appear as you type.
  4. Preview the documentation. The right panel renders your spec as clean API documentation, showing endpoints grouped by tag with expandable details.
  5. Export. Copy as YAML or JSON, or download the file to use with other OpenAPI tools.

OpenAPI 3.0 vs 3.1

OpenAPI 3.1 introduced full JSON Schema compatibility, meaning you can use standard JSON Schema keywords like oneOf, anyOf, and prefixItems directly in your spec. This is a significant improvement over 3.0, which used a modified subset of JSON Schema. However, many tools still primarily target 3.0, so check your toolchain's compatibility before upgrading.

Best Practices for Writing API Specs

  • Use descriptive operation IDs. The operationId field becomes function names in generated clients. Use clear, verb-based names like listUsers or createOrder.
  • Add examples. Include example values for request bodies and responses. This makes your documentation instantly more useful for developers.
  • Use tags consistently. Group related endpoints under tags. This organizes your documentation and helps developers find what they need.
  • Document errors. Don't just document the happy path. Include 400, 401, 403, 404, and 500 responses with meaningful descriptions.
  • Define reusable components. Put shared schemas in components/schemas and reference them with $ref. This keeps your spec DRY and consistent.

Integrating with Other Tools

Once your spec is ready, you can use it with tools like Swagger UI for interactive documentation, OpenAPI Generator for client/server code generation, or Prism for API mocking. Use the JSON Schema Validator to validate individual component schemas, or the Schema Converter to convert your schemas to TypeScript, Zod, or Pydantic models.