Fastify Route Development

This skill provides patterns for creating Fastify routes with TypeBox validation and OpenAPI documentation.

Directory Structure

Routes are located in app/src/routes/. Each route file exports a default async function that registers routes on a Fastify instance.

Route Template

import { type FastifyPluginAsyncTypebox, Type } from "@fastify/type-provider-typebox";
import { ErrorModelSchema } from "../schemas/index.js";

const routes: FastifyPluginAsyncTypebox = async (fastify) => {
  fastify.get(
    "/endpoint",
    {
      schema: {
        description: "Endpoint description for OpenAPI docs",
        tags: ["tag-name"],
        summary: "Short summary",
        querystring: Type.Object({
          param: Type.String({ description: "Query parameter" }),
        }),
        response: {
          200: Type.Object({
            status: Type.Literal("ok"),
            data: Type.String({ description: "Response data" }),
          }),
          422: ErrorModelSchema,
          500: ErrorModelSchema,
        },
      },
    },
    async (request, reply) => {
      const { param } = request.query;
      return { status: "ok", data: param };
    },
  );
};

export default routes;

OpenAPI Schema Requirements

1. Always include schema: Every route handler must have a schema property
2. Description and summary: Required for OpenAPI documentation
3. Tags: Group related endpoints
4. Response codes: Document all possible response status codes
5. Error responses: Use ErrorModelSchema from schemas/index.js for error status codes (400, 404, 422, 500, 503)
6. TypeBox types: Use Type from @fastify/type-provider-typebox
7. Schema discoverability: Only schemas referenced in route definitions appear in OpenAPI components.schemas

Authentication

For protected routes, use the fastify.authenticate preHandler:

import { ErrorModelSchema } from "../schemas/index.js";

fastify.get(
  "/protected",
  {
    preHandler: [fastify.authenticate],
    schema: {
      description: "Protected endpoint requiring authentication",
      tags: ["protected"],
      response: {
        200: Type.Object({ userId: Type.String() }),
        401: ErrorModelSchema,
        500: ErrorModelSchema,
      },
    },
  },
  async (request) => {
    return { userId: request.user.uid };
  },
);

HTTP Methods

Use appropriate HTTP methods:

• GET - Read operations
• POST - Create operations
• PUT - Full update operations
• PATCH - Partial update operations
• DELETE - Delete operations

Error Handling

Use @fastify/sensible HTTP error helpers:

// Throw errors
throw fastify.httpErrors.notFound("Resource not found");
throw fastify.httpErrors.badRequest("Invalid input");

// Reply methods
reply.notFound("Resource not found");
reply.badRequest("Invalid input");

Existing Routes

• routes/health.ts - Simple liveness probe at /health (returns { status: "healthy" })
• routes/schemas.ts - Schema discovery at /schemas/:schemaId
• routes/v1.ts - V1 API router that registers versioned modules under /v1
• modules/hello/routes.ts - Greeting endpoint at /v1/hello (GET and POST)
• modules/items/routes.ts - Items collection at /v1/items with cursor-based pagination and category filtering

Testing Requirements

Each route must have a corresponding test file in app/tests/unit/. Routes in src/routes/ have tests in tests/unit/routes/, and module routes in src/modules/ have tests in tests/unit/modules/.

Commands

cd app
npm run build       # Build and verify TypeScript compilation
npm run check       # Run Biome linter and formatter
npm run test        # Run all tests

Boundaries

• Do not create routes without TypeBox schemas
• Do not skip OpenAPI documentation (description, tags, summary)
• Always add corresponding unit tests for new routes