Contract Standards Skill

Standards for OpenAPI contract components that define API specifications and generate TypeScript types.

Purpose

Contract components are the single source of truth for API types:

1. Define API shape in OpenAPI 3.0 YAML
2. Generate TypeScript types consumed by server and webapp
3. Validate API consistency via Spectral linting
4. Enable type-safe development across the stack

Directory Structure

components/contract[-{name}]/
├── package.json          # Build scripts (generate:types, validate)
├── tsconfig.json         # TypeScript config for generated types
├── openapi.yaml          # OpenAPI 3.0 specification
├── .spectral.yaml        # Spectral linting rules (optional)
├── .gitignore            # Ignores generated/ directory
└── generated/            # Git-ignored generated output
    └── api-types.ts      # Generated TypeScript types

Config Schema

Contract components do not require application config from components/config/. They are build-time artifacts, not runtime services. The contract-scaffolding skill generates an openapi.yaml, package.json with type generation scripts, and a generated/ directory for TypeScript types.

OpenAPI Specification Standards

Info Section

openapi: '3.0.3'
info:
  title: Project API
  version: '1.0.0'
  description: API description

Path Naming

Rules:

• Use plural nouns for collections (/users, not /user)
• Use kebab-case for multi-word paths (/user-profiles)
• Use camelCase for path parameters ({userId})
• Avoid verbs in paths (use HTTP methods instead)

Operation IDs

Operation IDs become handler function names:

paths:
  /users:
    get:
      operationId: listUsers      # -> handleListUsers
    post:
      operationId: createUser     # -> handleCreateUser
  /users/{userId}:
    get:
      operationId: getUser        # -> handleGetUser
    put:
      operationId: updateUser     # -> handleUpdateUser
    delete:
      operationId: deleteUser     # -> handleDeleteUser

Rules:

• Use camelCase
• Start with verb: get, list, create, update, delete
• Be specific: getUserProfile, not getProfile

Request/Response Schemas

components:
  schemas:
    User:
      type: object
      required:
        - id
        - email
      properties:
        id:
          type: string
          format: uuid
        email:
          type: string
          format: email
        name:
          type: string
        createdAt:
          type: string
          format: date-time

    CreateUserRequest:
      type: object
      required:
        - email
      properties:
        email:
          type: string
          format: email
        name:
          type: string

    Error:
      type: object
      required:
        - code
        - message
      properties:
        code:
          type: string
        message:
          type: string

Naming Conventions:

• Resource schemas: User, Order, Task
• Request schemas: CreateUserRequest, UpdateOrderRequest
• Response wrappers (if needed): UserListResponse, PaginatedResponse
• Errors: Error, ValidationError

Standard Error Responses

Define reusable error responses:

components:
  responses:
    BadRequest:
      description: Invalid request
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    NotFound:
      description: Resource not found
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'
    Unauthorized:
      description: Authentication required
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/Error'

Health Endpoints

Health check endpoints are NOT defined in the contract. They are infrastructure endpoints implemented directly in the Operator layer:

• /health - Liveness probe
• /readiness - Readiness probe

These run on a separate port (e.g., 9090) from the main API.

Type Generation

Running Generation

<plugin-root>/fullstack-typescript/system/system-run.sh contract generate-types <component-name>

Generated Type Usage

Server and webapp consume types via workspace dependency:

// In server or webapp
import type { components, paths } from '@project/contract';

// Schema types
type User = components['schemas']['User'];
type CreateUserRequest = components['schemas']['CreateUserRequest'];

// Path types (for typed API clients)
type GetUserPath = paths['/users/{userId}']['get'];

Type Import Rules

• Always use import type - Contract types are compile-time only
• Never modify generated files - Regenerate instead
• Add to workspace dependencies - Use "workspace:*" version

Versioning

API Versioning Strategy

For most SDD projects, avoid versioning until you have external consumers.

Schema Versioning

Track changes in info.version:

info:
  version: '1.0.0'  # Bump on breaking changes

Validation

Spectral Linting

<plugin-root>/fullstack-typescript/system/system-run.sh contract validate <component-name>

Uses .spectral.yaml for custom rules (optional).

Required Validations

1. All paths have operationId
2. All schemas have required fields defined
3. Response schemas match request context
4. No unused schemas

Implementation Order

When adding a new endpoint:

Step 1: Design the Endpoint

1. Add path to openapi.yaml
2. Define request schema (if POST/PUT/PATCH)
3. Define response schema
4. Add operationId

Step 2: Validate

<plugin-root>/fullstack-typescript/system/system-run.sh contract validate <component-name>

Step 3: Generate Types

<plugin-root>/fullstack-typescript/system/system-run.sh contract generate-types <component-name>

Step 4: Implement in Server

Server endpoint implementation must follow backend-standards — it defines the CMDO handler → orchestrator → repository layering that contract endpoints are built upon.

Multi-Contract Projects

When a project has multiple contracts (e.g., public API vs internal API):

components/contracts/
├── public-api/           # External-facing API
│   └── openapi.yaml
└── internal-api/         # Service-to-service API
    └── openapi.yaml

Each contract:

• Has its own package name (@project/public-api)
• Generates its own types
• Is consumed independently by servers/webapps

Summary Checklist

Before committing contract changes:

• All paths have operationId
• Operation IDs follow camelCase verb convention
• Request/response schemas are defined
• Required fields are specified
• Standard error responses are used
• Types regenerated after spec changes
• Validation passes (contract validate)
• No health endpoints in contract (they're infrastructure)

Input / Output

This skill defines no input parameters or structured output.

Related Skills

• backend-standards — Delegate to this for server-side endpoint implementation. Defines the CMDO handler → orchestrator → repository layering that contract endpoints are built upon.
• frontend-standards — Delegate to this for webapp consumption of generated types. Defines MVVM patterns and TanStack Query hooks that use the TypeScript types generated from OpenAPI specs.