1. What It Is and Why You Need It

Fastify is a high-performance web framework for Node.js, inspired by Hapi and Express, but with a focus on speed and low memory consumption. It was created in 2016 by developers from the NearForm team and has since become one of the fastest solutions for building REST APIs, microservices, and web applications in JavaScript/TypeScript.

The main reason to use Fastify is its performance. According to benchmarks, it can handle 30-40% more requests per second compared to Express with the same resource consumption. This is achieved through an asynchronous architecture based on Node.js streams, efficient JSON parsing (via fast-json-stringify), and an optimized router based on Radix Tree (compressed prefix tree).

In addition to speed, Fastify offers built-in schema validation via JSON Schema, automatic response caching, out-of-the-box TypeScript support, an extensible plugin system, and excellent documentation. This makes it an ideal choice for production projects where stability and predictable performance under load are important.

2. Installation

Fastify is installed via npm (Node Package Manager). Make sure you have Node.js version 18 or higher installed (LTS recommended).

# Basic installation\nnpm install fastify\n\n# For TypeScript (optional)\nnpm install -D @types/node typescript\n\n# For working with cookies, sessions, etc.\nnpm install @fastify/cookie @fastify/session

If you use yarn or pnpm:

yarn add fastify\n# or\npnpm add fastify

3. Quick Start — Minimal Working Example

Create a file server.js and run it with node server.js.

// server.js\nconst fastify = require('fastify')({\n  logger: true // Enable built-in logger (pino)\n});\n\n// Define GET / route\nfastify.get('/', async (request, reply) => {\n  return { hello: 'world' };\n});\n\n// Start the server\nconst start = async () => {\n  try {\n    await fastify.listen({ port: 3000 });\n    console.log('Server running at http://localhost:3000');\n  } catch (err) {\n    fastify.log.error(err);\n    process.exit(1);\n  }\n};\n\nstart();

After starting, open your browser or run curl http://localhost:3000. You will receive the JSON response {"hello":"world"}.

4. Main Methods/Functions/Classes

4.1. fastify.get(path, options, handler)

Signature: fastify.get(path: string, opts?: RouteShorthandOptions, handler: RequestHandler)

What it does: Registers a handler for HTTP GET requests at the specified path.

fastify.get('/user/:id', async (request, reply) => {\n  const { id } = request.params;\n  return { userId: id, name: 'John Doe' };\n});

4.2. fastify.post(path, options, handler)

Signature: fastify.post(path: string, opts?: RouteShorthandOptions, handler: RequestHandler)

What it does: Registers a handler for HTTP POST requests. Automatically parses the request body (JSON, form-data, etc.).

fastify.post('/user', async (request, reply) => {\n  const { name, email } = request.body;\n  // Save user to database...\n  return { status: 'created', name, email };\n});

4.3. fastify.register(plugin, opts)

Signature:

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