fastify

Development

Fastify plugins, hooks, validation, serialization, and performance optimization patterns.

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Fastify Skill

Expert assistance for building high-performance APIs with Fastify.

Capabilities

Configure Fastify with plugins
Implement hooks for lifecycle management
Set up JSON Schema validation
Optimize serialization for performance
Build type-safe APIs with TypeScript
Create reusable plugins

Usage

Invoke this skill when you need to:

Build high-performance APIs
Implement schema validation
Create custom plugins
Optimize JSON serialization
TypeScript integration

Inputs

Parameter	Type	Required	Description
routePrefix	string	Yes	Route prefix
validation	boolean	No	Add JSON Schema validation
plugins	array	No	Plugins to use

Patterns

Application Setup

// src/app.ts
import Fastify, { FastifyInstance } from 'fastify';
import cors from '@fastify/cors';
import helmet from '@fastify/helmet';
import rateLimit from '@fastify/rate-limit';
import swagger from '@fastify/swagger';
import swaggerUi from '@fastify/swagger-ui';

import { usersRoutes } from './routes/users';
import { authRoutes } from './routes/auth';
import { errorHandler } from './plugins/error-handler';

export async function buildApp(): Promise<FastifyInstance> {
  const app = Fastify({
    logger: {
      level: process.env.LOG_LEVEL || 'info',
      transport: process.env.NODE_ENV !== 'production'
        ? { target: 'pino-pretty' }
        : undefined,
    },
    ajv: {
      customOptions: {
        removeAdditional: 'all',
        coerceTypes: true,
        useDefaults: true,
      },
    },
  });

  // Security plugins
  await app.register(helmet);
  await app.register(cors, {
    origin: process.env.CORS_ORIGIN || true,
    credentials: true,
  });
  await app.register(rateLimit, {
    max: 100,
    timeWindow: '1 minute',
  });

  // Documentation
  await app.register(swagger, {
    openapi: {
      info: {
        title: 'API Documentation',
        version: '1.0.0',
      },
      components: {
        securitySchemes: {
          bearerAuth: {
            type: 'http',
            scheme: 'bearer',
          },
        },
      },
    },
  });
  await app.register(swaggerUi, {
    routePrefix: '/docs',
  });

  // Custom plugins
  await app.register(errorHandler);

  // Routes
  await app.register(authRoutes, { prefix: '/api/auth' });
  await app.register(usersRoutes, { prefix: '/api/users' });

  // Health check
  app.get('/health', async () => ({
    status: 'ok',
    timestamp: new Date().toISOString(),
  }));

  return app;
}

Routes with Schema Validation

// src/routes/users.ts
import { FastifyPluginAsync } from 'fastify';
import { Type, Static } from '@sinclair/typebox';
import { UsersService } from '../services/users.service';

const UserSchema = Type.Object({
  id: Type.String(),
  name: Type.String(),
  email: Type.String({ format: 'email' }),
  role: Type.Union([Type.Literal('user'), Type.Literal('admin')]),
  createdAt: Type.String({ format: 'date-time' }),
});

const CreateUserSchema = Type.Object({
  name: Type.String({ minLength: 1 }),
  email: Type.String({ format: 'email' }),
  password: Type.String({ minLength: 8 }),
  role: Type.Optional(Type.Union([Type.Literal('user'), Type.Literal('admin')])),
});

const UpdateUserSchema = Type.Partial(CreateUserSchema);

const PaginationSchema = Type.Object({
  page: Type.Optional(Type.Number({ minimum: 1, default: 1 })),
  limit: Type.Optional(Type.Number({ minimum: 1, maximum: 100, default: 10 })),
  search: Type.Optional(Type.String()),
});

type User = Static<typeof UserSchema>;
type CreateUser = Static<typeof CreateUserSchema>;
type UpdateUser = Static<typeof UpdateUserSchema>;
type Pagination = Static<typeof PaginationSchema>;

export const usersRoutes: FastifyPluginAsync = async (fastify) => {
  const service = new UsersService();

  fastify.get<{ Querystring: Pagination }>('/', {
    schema: {
      tags: ['users'],
      querystring: PaginationSchema,
      response: {
        200: Type.Object({
          data: Type.Array(UserSchema),
          meta: Type.Object({
            total: Type.Number(),
            page: Type.Number(),
            limit: Type.Number(),
          }),
        }),
      },
    },
    preHandler: [fastify.authenticate],
  }, async (request) => {
    return service.findAll(request.query);
  });

  fastify.get<{ Params: { id: string } }>('/:id', {
    schema: {
      tags: ['users'],
      params: Type.Object({ id: Type.String() }),
      response: { 200: UserSchema },
    },
    preHandler: [fastify.authenticate],
  }, async (request, reply) => {
    const user = await service.findById(request.params.id);
    if (!user) {
      return reply.status(404).send({ error: 'User not found' });
    }
    return user;
  });

  fastify.post<{ Body: CreateUser }>('/', {
    schema: {
      tags: ['users'],
      body: CreateUserSchema,
      response: { 201: UserSchema },
    },
    preHandler: [fastify.authenticate, fastify.authorize(['admin'])],
  }, async (request, reply) => {
    const user = await service.create(request.body);
    return reply.status(201).send(user);
  });

  fastify.put<{ Params: { id: string }; Body: UpdateUser }>('/:id', {
    schema: {
      tags: ['users'],
      params: Type.Object({ id: Type.String() }),
      body: UpdateUserSchema,
      response: { 200: UserSchema },
    },
    preHandler: [fastify.authenticate],
  }, async (request) => {
    return service.update(request.params.id, request.body);
  });

  fastify.delete<{ Params: { id: string } }>('/:id', {
    schema: {
      tags: ['users'],
      params: Type.Object({ id: Type.String() }),
    },
    preHandler: [fastify.authenticate, fastify.authorize(['admin'])],
  }, async (request, reply) => {
    await service.delete(request.params.id);
    return reply.status(204).send();
  });
};

Hooks and Plugins

// src/plugins/auth.ts
import { FastifyPluginAsync, FastifyRequest } from 'fastify';
import fp from 'fastify-plugin';
import jwt from '@fastify/jwt';

declare module 'fastify' {
  interface FastifyInstance {
    authenticate: (request: FastifyRequest) => Promise<void>;
    authorize: (roles: string[]) => (request: FastifyRequest) => Promise<void>;
  }
}

declare module '@fastify/jwt' {
  interface FastifyJWT {
    payload: { id: string; email: string; role: string };
    user: { id: string; email: string; role: string };
  }
}

const authPlugin: FastifyPluginAsync = async (fastify) => {
  await fastify.register(jwt, {
    secret: process.env.JWT_SECRET!,
  });

  fastify.decorate('authenticate', async (request: FastifyRequest) => {
    await request.jwtVerify();
  });

  fastify.decorate('authorize', (roles: string[]) => {
    return async (request: FastifyRequest) => {
      await request.jwtVerify();
      if (!roles.includes(request.user.role)) {
        throw fastify.httpErrors.forbidden('Insufficient permissions');
      }
    };
  });
};

export default fp(authPlugin, {
  name: 'auth-plugin',
});

// src/plugins/error-handler.ts
import { FastifyPluginAsync } from 'fastify';
import fp from 'fastify-plugin';

const errorHandler: FastifyPluginAsync = async (fastify) => {
  fastify.setErrorHandler((error, request, reply) => {
    fastify.log.error(error);

    if (error.validation) {
      return reply.status(400).send({
        error: 'Validation Error',
        details: error.validation,
      });
    }

    const statusCode = error.statusCode || 500;
    const message = statusCode === 500 && process.env.NODE_ENV === 'production'
      ? 'Internal Server Error'
      : error.message;

    return reply.status(statusCode).send({ error: message });
  });
};

export default fp(errorHandler, {
  name: 'error-handler',
});

Custom Hooks

// Lifecycle hooks
fastify.addHook('onRequest', async (request, reply) => {
  request.startTime = Date.now();
});

fastify.addHook('onResponse', async (request, reply) => {
  const duration = Date.now() - request.startTime;
  request.log.info({ duration }, 'Request completed');
});

fastify.addHook('onSend', async (request, reply, payload) => {
  // Modify response before sending
  return payload;
});

Best Practices

Use JSON Schema for validation
Leverage TypeBox for TypeScript schemas
Create reusable plugins with fastify-plugin
Use hooks for cross-cutting concerns
Enable schema serialization for performance

Target Processes

high-performance-api
nodejs-microservices
api-development
backend-optimization