Dev

Mock OpenAPI Spec Generator

A mock OpenAPI spec generator lets you produce a complete, valid OpenAPI 3.0 YAML document in seconds — without hand-writing boilerplate. Enter a resource name like "orders" or "products", set your API title and version, and the generator builds a full specification including list, create, get, update, and delete endpoints, request/response schemas, and JWT bearer security definitions. The result conforms to the OpenAPI 3.0 standard recognized by Swagger UI, Redoc, Postman, and every major code-generation pipeline. Starting an API from a blank YAML file wastes time on repetitive structure. This tool handles the scaffolding — paths, operationIds, 200/201/404 responses, component schemas — so you can focus on customizing business logic rather than memorizing spec syntax. The generated YAML passes validation tools like Spectral and swagger-parser without modification. Practical uses go beyond documentation. Paste the output into openapi-generator-cli to scaffold a TypeScript or Python client in one command. Import it into Postman to auto-create a collection with pre-built requests. Feed it to Schemathesis or Dredd for contract testing before your backend is even built. Teams doing API-first design use outputs like this to align frontend and backend engineers on the contract before a single line of implementation code is written. The spec follows REST conventions closely: plural resource paths, a separate detail path with a path parameter, and reusable component schemas to keep the document DRY. Whether you need a quick prototype, a test fixture, or a starting point for a production API document, this generator gives you a solid, standards-compliant foundation.

How to Use

  1. Type your REST resource name (e.g., "orders", "products") into the Resource Name field.
  2. Set the API Title and Version fields to match your project's branding and semantic version.
  3. Click Generate to produce the complete OpenAPI 3.0 YAML document.
  4. Copy the output and paste it into Swagger Editor, save it as a .yaml file, or import it directly into Postman.

Use Cases

  • •Scaffolding OpenAPI 3.0 docs for a new REST resource in seconds
  • •Importing a ready-made YAML collection directly into Postman
  • •Generating a TypeScript or Python client with openapi-generator-cli
  • •Creating contract test fixtures for Schemathesis or Dredd pipelines
  • •Aligning frontend and backend teams on API shape before coding starts
  • •Prototyping API designs inside Swagger Editor without writing YAML by hand
  • •Producing mock server definitions for tools like Prism or WireMock
  • •Demonstrating REST API structure in technical interviews or documentation tutorials

Tips

  • →Use singular or plural resource names consistently — the generator outputs plural paths, so enter the plural form ("invoices") to avoid mismatched paths like /invoice.
  • →After generating, add an 'example' field to each schema property; Swagger UI and Prism use examples to render realistic mock responses.
  • →Bump the version field to match semver (e.g., 2.0.0 vs 1.0.0) when making breaking changes — tools like openapi-diff use this to detect incompatibilities.
  • →Combine multiple generated specs by merging their paths and components blocks; generate one spec per resource and use a tool like swagger-merger to assemble the full API.
  • →If your API is public and needs no auth, delete the global 'security' key and the securitySchemes component to avoid confusing false authorization prompts in Swagger UI.
  • →For contract testing with Schemathesis, point it directly at the saved YAML file using: schemathesis run api.yaml --base-url http://localhost:8000 to catch response schema mismatches early.

FAQ

Is the generated YAML valid OpenAPI 3.0?

Yes. The output conforms to the OpenAPI 3.0.x specification and passes validation with tools like swagger-parser and Stoplight Spectral without modification. It includes required fields such as openapi version string, info block, paths, and components/schemas, so it is accepted by Swagger UI, Redoc, and Postman without extra editing.

How do I import the spec into Postman?

Copy the generated YAML, open Postman, go to Import, choose Raw Text, and paste it in. Postman will create a collection with pre-configured requests for every generated endpoint. You can then set environment variables for your base URL and JWT token and start making requests immediately.

How do I use the output with openapi-generator to create a client SDK?

Save the YAML to a file, for example api.yaml, then run: openapi-generator-cli generate -i api.yaml -g typescript-fetch -o ./client. Replace typescript-fetch with any supported generator (python, java, go, etc.). The generated client will include typed models and service methods matching your resource.

What operations does the generated spec include?

The spec includes five standard REST operations: GET /resource (list all), POST /resource (create), GET /resource/{id} (get one), PUT /resource/{id} (update), and DELETE /resource/{id}. Each operation has request/response schemas, appropriate HTTP status codes, and a JWT bearer security requirement.

Can I use this for API-first development before writing backend code?

Yes. Generate the spec, commit it to your repo, and share it with your team as the contract. Frontend developers can point a mock server like Prism (npx @stoplight/prism-cli mock api.yaml) at the file to get a live HTTP mock immediately, letting UI development proceed before the backend is implemented.

How do I change the resource name to something like 'invoices' or 'products'?

Type your desired resource name into the Resource Name field before generating. The tool uses that string to name the paths (/invoices, /invoices/{id}), schema components (Invoice, InvoiceList), and operationIds throughout the document, so the output is consistent and meaningful for your actual domain.

Does the spec include authentication?

Yes. The generated spec defines a JWT bearer security scheme under components/securitySchemes and applies it globally. This means tools like Swagger UI will show an Authorize button, and code generators will include token-injection logic in the produced clients. You can remove the security block if your API is public.

Can I validate the generated spec with Spectral or other linters?

Yes. Save the output as api.yaml and run: npx @stoplight/spectral-cli lint api.yaml --ruleset @stoplight/spectral-oas. The generated document is structured to pass the built-in OAS ruleset. Any warnings you see will be opportunities to add descriptions or examples as you customize the spec for production.