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name: openapi-spec-generation description: Generate and maintain OpenAPI 3.1 specifications from code, design-first specs, and validation patterns. Use when creating API documentation, generating SDKs, or ensuring API contract compliance.

OpenAPI Spec Generation

Comprehensive patterns for creating, maintaining, and validating OpenAPI 3.1 specifications for RESTful APIs.

When to Use This Skill

• Creating API documentation from scratch
• Generating OpenAPI specs from existing code
• Designing API contracts (design-first approach)
• Validating API implementations against specs
• Generating client SDKs from specs
• Setting up API documentation portals

Core Concepts

1. OpenAPI 3.1 Structure

openapi: 3.1.0
info:
  title: API Title
  version: 1.0.0
servers:
  - url: https://api.example.com/v1
paths:
  /resources:
    get: ...
components:
  schemas: ...
  securitySchemes: ...

2. Design Approaches

| Approach | Description | Best For | | ---------------- | ---------------------------- | ------------------- | | Design-First | Write spec before code | New APIs, contracts | | Code-First | Generate spec from code | Existing APIs | | Hybrid | Annotate code, generate spec | Evolving APIs |

Templates and detailed worked examples

Full template library and detailed worked examples live in references/details.md. Read that file when you need the concrete templates.

Best Practices

Do's

• Use $ref - Reuse schemas, parameters, responses
• Add examples - Real-world values help consumers
• Document errors - All possible error codes
• Version your API - In URL or header
• Use semantic versioning - For spec changes

Don'ts

• Don't use generic descriptions - Be specific
• Don't skip security - Define all schemes
• Don't forget nullable - Be explicit about null
• Don't mix styles - Consistent naming throughout
• Don't hardcode URLs - Use server variables