OpenAPI app builder

What it does

Share your API spec and chosen stack. Check the contract, build the app and get code with tests and setup notes.

What goes in and out

You give it

• Your OpenAPI spec as a link, a file or pasted text.
• Your target framework and version, such as Node with Express.
• Your login method, if the spec does not name one (optional).
• Business rules the spec leaves open (optional).
• Whether you want a database, Docker or pagination (optional).
• Your question (optional)

You get

• A project folder layout for your chosen framework.
• Route handlers for every path and method in your spec.
• Data types built from your spec's schemas.
• Service code, tests and example requests.
• A README, .gitignore and .env.example.
• A list of gaps and unclear parts in your spec.

How the task works

• Read the API contract. Check paths, methods, schemas and auth rules. Ask about behavior that the contract leaves unclear.
• Build the app layers. Create route handlers, data types, service logic, config and data access only where the brief requires them.
• Check against the spec. Add tests and sample requests. Run available checks and report any missing tool, rule or failed case.

Full instructions

• Open Claude, ChatGPT or Gemini and paste the skill text, or add the skill folder if your tool takes files.
• Paste your OpenAPI spec, or give a link if your AI can open web pages.
• Say which framework and version you want. If you skip this, your AI should ask before it writes code.
• Answer its questions about database, login method, Docker and tests.
• Read the list of gaps in your spec, then check the routes against your spec.
• Copy the files into a folder. To install and run the tests, you need code running on your own computer.

Full instruction file

Generate Application from OpenAPI Spec

Your goal is to generate a complete, working application from an OpenAPI specification using the active framework's conventions and best practices.

Before you start

Use the material below to do this job. If facts or tool access are missing, explain what you can finish and what must wait.

What you need (use your own material or the linked skill):

• Your API spec (yours): the API's endpoints, data shapes, sign-in method and errors, such as an OpenAPI file.

Makes it better (optional):

• Your question (yours): the decision or problem, and what a good outcome looks like.

How to start:

1. Look first. Use what they've already attached, pasted or put in their about-me note. In a coding assistant with file access, look in the project too for these by name.
2. Check what's missing. Look for your API spec, your question. They can attach files, paste the details, or share a file path your assistant can read. Ask only for missing facts that change the result. If they ask you to start with what they have, complete the parts you can and mark the gaps.
3. Do the job. Follow the skill below with the facts and tools you have. Mark each gap with MISSING: where it belongs and never invent a fact to fill it.

Input Requirements

1. OpenAPI Specification: Provide either:

   • A URL to the OpenAPI spec (e.g., https://api.example.com/openapi.json)
   • A local file path to the OpenAPI spec
   • The full OpenAPI specification content pasted directly

2. Project Details (if not in spec):

   • Project name and description
   • Target framework and version
   • Package/namespace naming conventions
   • Authentication method (if not specified in OpenAPI)

Generation Process

Step 1: Analyze the OpenAPI Specification

• Validate the OpenAPI spec for completeness and correctness
• Identify all endpoints, HTTP methods, request/response schemas
• Extract authentication requirements and security schemes
• Note data model relationships and constraints
• Flag any ambiguities or incomplete definitions

Step 2: Design Application Architecture

• Plan directory structure appropriate for the framework
• Identify controller/handler grouping by resource or domain
• Design service layer organization for business logic
• Plan data models and entity relationships
• Design configuration and initialization strategy

Step 3: Generate Application Code

• Create project structure with build/package configuration files
• Generate models/DTOs from OpenAPI schemas
• Generate controllers/handlers with route mappings
• Generate service layer with business logic
• Generate repository/data access layer if applicable
• Add error handling, validation, and logging
• Generate configuration and startup code

Step 4: Add Supporting Files

• Generate appropriate unit tests for services and controllers
• Create README with setup and running instructions
• Add .gitignore and environment configuration templates
• Generate API documentation files
• Create example requests/integration tests

Output Structure

The generated application will include:

project-name/
├── README.md                      # Setup and usage instructions
├── [build-config]                 # Framework-specific build files (pom.xml, build.gradle, package.json, etc.)
├── src/
│   ├── main/
│   │   ├── [language]/
│   │   │   ├── controllers/       # HTTP endpoint handlers
│   │   │   ├── services/          # Business logic
│   │   │   ├── models/            # Data models and DTOs
│   │   │   ├── repositories/      # Data access (if applicable)
│   │   │   └── config/            # Application configuration
│   │   └── resources/             # Configuration files
│   └── test/
│       ├── [language]/
│       │   ├── controllers/       # Controller tests
│       │   └── services/          # Service tests
│       └── resources/             # Test configuration
├── .gitignore
├── .env.example                   # Environment variables template
└── docker-compose.yml             # Optional: Docker setup (if applicable)

Best Practices Applied

• Framework Conventions: Follows framework-specific naming, structure, and patterns
• Separation of Concerns: Clear layers with controllers, services, and repositories
• Error Handling: Comprehensive error handling with meaningful responses
• Validation: Input validation and schema validation throughout
• Logging: Structured logging for debugging and monitoring
• Testing: Unit tests for services and controllers
• Documentation: Inline code documentation and setup instructions
• Security: Implements authentication/authorization from OpenAPI spec
• Scalability: Design patterns support growth and maintenance

Next Steps

After generation:

1. Review the generated code structure and make customizations as needed
2. Install dependencies according to framework requirements
3. Configure environment variables and database connections
4. Run tests to verify generated code
5. Start the development server
6. Test endpoints using the provided examples

After this

When you've handed it back, suggest what they could do next in one short question. It's a suggestion: if they're done, that's fine. Offer these, and say they can type their own:

• The Software developer from specifications. It takes the document and codebase.
• The API spec writer. It takes the codebase.
• The REST API designer. It takes the codebase. If they pick one and that skill is added here, carry straight on with what you just made. If not, give the link and say what to bring.

Questions to Ask if Needed

• Should the application include database/ORM setup, or just in-memory/mock data?
• Do you want Docker configuration for containerization?
• Should authentication be JWT, OAuth2, API keys, or basic auth?
• Do you need integration tests or just unit tests?
• Any specific database technology preferences?
• Should the API include pagination, filtering, and sorting examples?