Openapi Spec Generation

When to use this skill

Use Openapi Spec Generation when an AI agent needs a reusable SKILL.md workflow for this job: 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.

When not to use it

Skip Openapi Spec Generation when the task is outside the coding category, or when a more specific skill in this directory already covers the same workflow with clearer triggers.

How to install

1. Personal install: create ~/.claude/skills/openapi-spec-generation/SKILL.md (and any bundled scripts) so Claude Code, Claude Desktop, and compatible agents can load it in every project.
2. Project install: commit the same folder at .claude/skills/openapi-spec-generation/ so teammates get the skill with the repo.
3. Restart the agent session after copying files so it re-scans the skills directory, then ask for the task in words that match the skill description.

Full install guide for Claude, Cursor, and Codex

What this skill does

# 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

```yaml 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

Intended uses

• 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