fastify-v5_skill

Overview

This skill integrates TypeBox schemas with Fastify to build type-safe REST APIs in TypeScript. It provides patterns for schema-driven route definitions, automatic JSON Schema-based validation, and OpenAPI generation. Use it to enforce request/response contracts and get end-to-end type inference from schemas.

How this skill works

Create TypeBox schemas for params, query, body, and responses and attach them to Fastify route schema objects. Instantiate Fastify with the TypeBox type provider so request types are inferred from schemas and response validation runs automatically. Configure OpenAPI generation via Fastify Swagger plugins using operationId and tags for clean documentation.

When to use it

• Building Fastify v5+ REST APIs with full TypeScript type safety
• Enforcing runtime validation for request params, query, body, and responses
• Generating OpenAPI/Swagger docs directly from route schemas
• Developing reusable plugins or hooks that rely on typed request shapes
• Writing blackbox tests using Fastify inject() with known input/output contracts

Best practices

• Always use fastify.withTypeProvider<TypeBoxTypeProvider>() for routes
• Define response schemas for every expected status code, including errors
• Prefer Type.* constructors (Type.Object, Type.String, etc.) for schemas
• Include operationId and tags in schema for consistent OpenAPI output
• Avoid mixing different schema libraries in the same route to prevent conflicts

Example use cases

• User CRUD API: params, body and 200/404 response schemas for typed handlers
• Auth endpoints: validate request bodies and define standardized error responses
• File streaming or SSE endpoints: declare response type and set proper headers
• Plugin development: build fastify-plugin modules that register typed routes
• Automated API docs: emit OpenAPI spec from TypeBox schemas for client codegen