YepAPI/skills

Express & Fastify

Rules

• Organize routes by domain: routes/users.ts, routes/orders.ts — one router per resource
• Validate all input with Zod: parse req.body, req.params, req.query before processing
• Centralized error handler: catch-all middleware (Express) or setErrorHandler (Fastify)
• Return consistent error format: { error: { code: string, message: string, details?: unknown } }
• TypeScript: type request/response with generics — Request<Params, ResBody, ReqBody, Query>
• Middleware order: CORS, body parser, auth, rate limiting, routes, error handler
• Use async route handlers — wrap with error catching or use express-async-errors
• Fastify: use the plugin system to encapsulate routes and decorators — fastify.register()
• Fastify schemas: define JSON Schema or use @fastify/type-provider-zod for validation + serialization
• Health check: GET /health — return 200 with DB/Redis connectivity status
• Graceful shutdown: listen for SIGTERM, stop accepting connections, finish in-flight requests

Patterns

// Express + Zod validation
import { Router } from "express";
import { z } from "zod";

const router = Router();
const CreateUserSchema = z.object({ email: z.string().email(), name: z.string().min(1) });

router.post("/users", async (req, res, next) => {
  try {
    const body = CreateUserSchema.parse(req.body);
    const user = await createUser(body);
    res.status(201).json(user);
  } catch (err) { next(err); }
});

// Fastify + Zod type provider
import Fastify from "fastify";
import { serializerCompiler, validatorCompiler, ZodTypeProvider } from "fastify-type-provider-zod";

const app = Fastify().withTypeProvider<ZodTypeProvider>();
app.setValidatorCompiler(validatorCompiler);
app.setSerializerCompiler(serializerCompiler);

app.post("/users", { schema: { body: CreateUserSchema } }, async (req) => {
  return createUser(req.body); // fully typed
});

Avoid

• Putting business logic in route handlers — extract to service/domain layer
• Forgetting async error handling in Express — unhandled rejections crash the process
• Importing all routes in one file — use router.use() or Fastify plugins for modularity
• Skipping input validation because "the frontend validates" — always validate server-side