TechnicalFree
Draft an OpenAPI specification from your endpoints
List your endpoints and get an OpenAPI 3.1 YAML draft with paths, schemas, authentication and error responses, ready to check in a validator.
River's OpenAPI Specification Generator drafts OpenAPI 3.1 YAML from your endpoint descriptions. You provide endpoints, methods, and parameters, and the AI writes comprehensive specifications including paths, request/response schemas, authentication, error responses, and examples. Whether you're documenting APIs, generating client SDKs, or enabling API testing, you get professional OpenAPI specs to check in a validator and then load into Swagger UI or code generation tools.
Unlike writing a specification by hand from a blank file, you start from a structured draft. The AI understands OpenAPI conventions (proper schemas, reusable components, correct data types, example values), follows REST best practices, and follows the OpenAPI 3.1 structure. You get machine-readable API documentation that integrates with the OpenAPI ecosystem.
This tool is perfect for backend developers documenting APIs, teams using API-first development, organizations standardizing API specs, and developers needing Swagger documentation. If you have APIs without formal specs, or if manual OpenAPI writing feels tedious, this tool helps. Use it to create specifications that power documentation, testing, and SDK generation.
What Makes OpenAPI Specs Effective
OpenAPI specifications succeed when they accurately describe APIs and enable tooling. Effective specs include all endpoints with proper HTTP methods, complete request/response schemas with examples, authentication and security schemes, error response documentation, reusable components for common patterns, and valid YAML syntax. Weak specs have incomplete schemas or invalid structure. Strong specs enable automatic documentation generation, client SDK creation, API testing, and contract validation.
The best OpenAPI specs follow consistent patterns. Use components for reusable schemas (User, Error). Define security schemes once, reference everywhere. Include realistic examples in schemas. Document all required and optional parameters. Specify response codes with descriptions. Use proper data types and formats (date-time, email, uuid). Tag endpoints logically for documentation grouping. This structure makes specs both human-readable and machine-processable.
To improve OpenAPI specs, validate with OpenAPI validators before publishing. Test with Swagger UI (does documentation render correctly?). Generate client SDKs (do they work?). Keep specs synchronized with actual API behavior. Version your specs with API versions. Use description fields generously (explain what things do). Include working examples (help developers understand). Remember: OpenAPI spec is contract between API provider and consumers. Clear, accurate, complete specs enable successful API integration.
How It Works
List API endpoints
Provide endpoints, methods, parameters, and descriptions
AI generates OpenAPI spec
Our AI creates complete YAML specification
Review and validate
Check spec, add specific details, validate YAML
Use with tooling
Import to Swagger UI, generate SDKs, enable API testing
What You Get
- OpenAPI 3.1 draft in YAML
- All endpoints with request/response schemas
- Authentication and security definitions
- Reusable components and examples
- Structured to pass a validator once you confirm the marked details
- Usable with Swagger UI and code generators after validation
Common questions
Which OpenAPI version does it write?
OpenAPI 3.1 by default. Version 3.2 was released in September 2025 with no breaking changes from 3.1, and 3.0 is still common in older tools; ask in chat for either. Swagger 2.0 is the older format that OpenAPI 3 replaced. Always run the draft through a validator before relying on it.
Can I generate client SDKs from this spec?
Yes! OpenAPI specs work with code generators like OpenAPI Generator, Swagger Codegen, and language-specific tools. Once you have valid spec, you can generate client libraries for JavaScript, Python, Java, Go, and many other languages automatically.
How do I keep OpenAPI spec synchronized with actual API?
Best practice: generate specs from code annotations or use spec-first development. Some frameworks (FastAPI, NestJS) generate OpenAPI specs automatically from code. Alternatively, use contract testing to verify API matches spec. Manual specs require discipline to keep updated with code changes.
Should I include examples in the spec?
Yes, absolutely. Examples in request/response schemas help developers understand expected data format. They also improve generated documentation and enable better testing. Good examples are realistic, show typical use cases, and include edge cases where helpful.
What's the difference between OpenAPI and REST API documentation?
OpenAPI is machine-readable specification format. REST API documentation is human-readable explanation. OpenAPI specs power tools that generate both documentation and code. You can have OpenAPI spec generate beautiful documentation automatically using Swagger UI, Redoc, or similar tools. Spec is source of truth.
Draft an OpenAPI specification from your endpoints
Describe what you need, add any files you have, and your workspace opens with the work already underway.