# API Design Contracts > API contract-first design using OpenAPI/Swagger for REST and AsyncAPI Use when this capability is needed. - Skill: `tomevault-io/api-design-contracts` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/api-design-contracts` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/api-design-contracts/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Integrations & APIs - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/api-design-contracts --- # Api Design Contracts ## Skill Profile *(Select at least one profile to enable specific modules)* - [ ] **DevOps** - [x] **Backend** - [ ] **Frontend** - [ ] **AI-RAG** - [ ] **Security Critical** ## Overview API contract-first design using OpenAPI/Swagger for REST and AsyncAPI for events to create clear contracts, support backward compatibility, and enable contract testing between services. This skill enables contract-first development, type safety through auto-generated clients, clear versioning strategy, and early detection of breaking changes. ## Why This Matters - **Contract-first**: Design API before implementation, reduce rework - **Type safety**: Auto-generate clients from contract - **Backward compatibility**: Clear versioning strategy - **Contract testing**: Detect breaking changes early --- ## Core Concepts & Rules ### 1. Core Principles - Follow established patterns and conventions - Maintain consistency across codebase - Document decisions and trade-offs ### 2. Implementation Guidelines - Start with the simplest viable solution - Iterate based on feedback and requirements - Test thoroughly before deployment ## Inputs / Outputs / Contracts * **Inputs**: - API requirements and use cases - OpenAPI/AsyncAPI specification files - Versioning strategy documentation - Consumer contract files * **Entry Conditions**: - OpenAPI/AsyncAPI specification is created - Versioning strategy is defined - Contract testing framework is configured * **Outputs**: - Validated OpenAPI/AsyncAPI specifications - Auto-generated TypeScript types - Generated API clients - Contract test results * **Artifacts Required (Deliverables)**: - OpenAPI specification file - AsyncAPI specification file (if events) - Contract tests - Generated types and clients * **Acceptance Evidence**: - OpenAPI spec is valid - Types are generated correctly - Contract tests pass - Breaking changes are detected * **Success Criteria**: - 100% of endpoints documented - 100% of contract tests pass - Breaking changes detected before deployment - Type safety maintained ## Skill Composition * **Depends on**: N/A * **Compatible with**: [secrets-key-management](../71-infrastructure-patterns/secrets-key-management/SKILL.md) * **Conflicts with**: Code-first development without contracts * **Related Skills**: [backend-api](../03-backend-api/SKILL.md) --- ## Quick Start / Implementation Example 1. Review requirements and constraints 2. Set up development environment 3. Implement core functionality following patterns 4. Write tests for critical paths 5. Run tests and fix issues 6. Document any deviations or decisions ```python # Example implementation following best practices def example_function(): # Your implementation here pass ``` ## Assumptions / Constraints / Non-goals * **Assumptions**: - Development environment is properly configured - Required dependencies are available - Team has basic understanding of domain * **Constraints**: - Must follow existing codebase conventions - Time and resource limitations - Compatibility requirements * **Non-goals**: - This skill does not cover edge cases outside scope - Not a replacement for formal training ## Compatibility & Prerequisites * **Supported Versions**: - Python 3.8+ - Node.js 16+ - Modern browsers (Chrome, Firefox, Safari, Edge) * **Required AI Tools**: - Code editor (VS Code recommended) - Testing framework appropriate for language - Version control (Git) * **Dependencies**: - Language-specific package manager - Build tools - Testing libraries * **Environment Setup**: - `.env.example` keys: `API_KEY`, `DATABASE_URL` (no values) ## Test Scenario Matrix (QA Strategy) | Type | Focus Area | Required Scenarios / Mocks | | :--- | :--- | :--- | | **Unit** | Core Logic | Must cover primary logic and at least 3 edge/error cases. Target minimum 80% coverage | | **Integration** | DB / API | All external API calls or database connections must be mocked during unit tests | | **E2E** | User Journey | Critical user flows to test | | **Performance** | Latency / Load | Benchmark requirements | | **Security** | Vuln / Auth | SAST/DAST or dependency audit | | **Frontend** | UX / A11y | Accessibility checklist (WCAG), Performance Budget (Lighthouse score) | ## Technical Guardrails & Security Threat Model ### 1. Security & Privacy (Threat Model) * **Top Threats**: Injection attacks, authentication bypass, data exposure - [ ] **Data Handling**: Sanitize all user inputs to prevent Injection attacks. Never log raw PII - [ ] **Secrets Management**: No hardcoded API keys. Use Env Vars/Secrets Manager - [ ] **Authorization**: Validate user permissions before state changes ### 2. Performance & Resources - [ ] **Execution Efficiency**: Consider time complexity for algorithms - [ ] **Memory Management**: Use streams/pagination for large data - [ ] **Resource Cleanup**: Close DB connections/file handlers in finally blocks ### 3. Architecture & Scalability - [ ] **Design Pattern**: Follow SOLID principles, use Dependency Injection - [ ] **Modularity**: Decouple logic from UI/Frameworks ### 4. Observability & Reliability - [ ] **Logging Standards**: Structured JSON, include trace IDs `request_id` - [ ] **Metrics**: Track `error_rate`, `latency`, `queue_depth` - [ ] **Error Handling**: Standardized error codes, no bare except - [ ] **Observability Artifacts**: - **Log Fields**: timestamp, level, message, request_id - **Metrics**: request_count, error_count, response_time - **Dashboards/Alerts**: High Error Rate > 5% ## Agent Directives & Error Recovery *(ข้อกำหนดสำหรับ AI Agent ในการคิดและแก้ปัญหาเมื่อเกิดข้อผิดพลาด)* - **Thinking Process**: Analyze root cause before fixing. Do not brute-force. - **Fallback Strategy**: Stop after 3 failed test attempts. Output root cause and ask for human intervention/clarification. - **Self-Review**: Check against Guardrails & Anti-patterns before finalizing. - **Output Constraints**: Output ONLY the modified code block. Do not explain unless asked. ## Definition of Done (DoD) Checklist - [ ] Tests passed + coverage met - [ ] Lint/Typecheck passed - [ ] Logging/Metrics/Trace implemented - [ ] Security checks passed - [ ] Documentation/Changelog updated - [ ] Accessibility/Performance requirements met (if frontend) ## Anti-patterns / Pitfalls * ⛔ **Don't**: Log PII, catch-all exception, N+1 queries * ⚠️ **Watch out for**: Common symptoms and quick fixes * 💡 **Instead**: Use proper error handling, pagination, and logging ## Reference Links & Examples * Internal documentation and examples * Official documentation and best practices * Community resources and discussions ## Versioning & Changelog * **Version**: 1.0.0 * **Changelog**: - 2026-02-22: Initial version with complete template structure --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/amnadtaowsoam) — claim your Tome and manage your conversions.