openapi-generator

Scan your Express source directory to extract route definitions and JSDoc metadata like @summary, @description, and @tags. The generator converts Express-style :param paths to OpenAPI {param} syntax and builds path objects with default responses.

Use the TypeScript compiler API to walk type nodes: primitives map to string, number, or boolean; arrays map to items schemas; object properties become schema properties with required fields derived from optional modifiers. String literal unions become enums.

Yes, Fastify integrates with @fastify/swagger and @fastify/swagger-ui to serve OpenAPI specs and interactive docs at a route prefix like /docs. Route schemas defined in Fastify are used directly to build the specification.

Yes, NestJS uses @nestjs/swagger decorators such as @ApiTags, @ApiOperation, @ApiResponse, and @ApiBody on controllers to produce OpenAPI documentation. DTO classes define request and response schemas.

Use @apidevtools/swagger-parser to validate the spec file programmatically. It parses the YAML or JSON, checks structural correctness, and reports validation errors before you publish or import the spec.

Scanned specs rely on JSDoc comments and type information, so undocumented routes get generic summaries and default responses. Complex runtime behavior like dynamic middleware-based validation may not be captured without manual annotation.