Fastify Node.js Framework Cheat Sheet

Updated 2026-05-16

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Fastify is a high-performance web framework for Node.js designed with developer experience and minimal overhead as core principles. Built from the ground up with performance in mind, it leverages a powerful plugin architecture, JSON Schema-based validation, and schema-driven serialization to deliver throughput rates 2-4× faster than Express. The framework's encapsulation model ensures that decorators, hooks, and plugins remain isolated within their registration context, preventing unintended side effects across application boundaries. A critical mental model: Fastify compiles JSON schemas at startup into highly optimized functions, meaning validation and serialization happen at near-native speed rather than runtime interpretation cost typical of other frameworks.

What This Cheat Sheet Covers

This topic spans 24 focused tables and 196 indexed concepts, 138 flashcards. Below is a complete table-by-table outline of this topic, spanning foundational concepts through advanced details.

Table 1: Server Initialization and ConfigurationTable 2: Route Definition MethodsTable 3: Request Object PropertiesTable 4: Reply Object MethodsTable 5: JSON Schema ValidationTable 6: Lifecycle HooksTable 7: Plugin SystemTable 8: DecoratorsTable 9: Error HandlingTable 10: SerializationTable 11: Content Type ParsingTable 12: Testing UtilitiesTable 13: Pino LoggingTable 14: TypeScript SupportTable 15: Performance OptimizationTable 16: Common PluginsTable 17: Route ConfigurationTable 18: Server MethodsTable 19: Streaming and Advanced ResponseTable 20: Constraints and VersioningTable 21: Graceful ShutdownTable 22: Request Context and ScopeTable 23: Security Best PracticesTable 24: Middleware Compatibility

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Table 1: Server Initialization and Configuration

The options you pass to the fastify() factory shape how the whole server behaves — from logging and body-size guards to proxy trust, routing quirks, and protocol choice. These are the knobs you set once at startup, and getting trustProxy, bodyLimit, and the timeout values right early saves a lot of grief in production behind load balancers.

Option	Example	Description
logger	`fastify({ logger: true })`	• Enables Pino logger with default 'info' level • accepts boolean or config object with level, stream, and serializers
bodyLimit	`fastify({ bodyLimit: 2097152 })`	• Sets maximum request body size in bytes • defaults to 1048576 (1 MiB) to prevent memory exhaustion
trustProxy	`fastify({ trustProxy: true })`	• Enables proxied headers like X-Forwarded-For • required for accurate client IP behind load balancers or reverse proxies
ignoreTrailingSlash	`fastify({ ignoreTrailingSlash: true })`	• Treats `/users` and `/users/` as same route • simplifies routing logic by normalizing URL patterns
caseSensitive	`fastify({ caseSensitive: false })`	• Makes route paths case-insensitive • treats `/Users` and `/users` as identical routes
requestIdHeader	`fastify({ requestIdHeader: 'x-request-id' })`	• Reads existing request ID from header • useful for distributed tracing across microservices
genReqId	`genReqId: (req) => uuid()`	• Custom request ID generator function • defaults to auto-incrementing number for each instance
connectionTimeout	`fastify({ connectionTimeout: 30000 })`	• Sets idle connection timeout in milliseconds • defaults to 0 (no timeout) for HTTP/1.1
keepAliveTimeout	`fastify({ keepAliveTimeout: 72000 })`	• Sets keep-alive timeout for reusing connections • defaults to 72 seconds to match Node.js behavior
maxParamLength	`fastify({ maxParamLength: 200 })`	• Limits URL parameter length • defaults to 100 characters to prevent abuse
http2	`fastify({ http2: true })`	• Enables HTTP/2 server with multiplexing and header compression • requires Node.js 8.8+
https	`https: { key, cert }`	• Provides TLS credentials for HTTPS server • accepts key and cert file contents or paths

Table 2: Route Definition Methods

Fastify gives you both terse shorthands (get, post) and a full route() declaration when you need schemas, hooks, and constraints in one place. The patterns here cover the everyday cases — static paths, parametric :id segments, wildcards, and prefixed plugin groups — and knowing which form to reach for keeps route files readable as an API grows.

Method	Example	Description
shorthand GET	`fastify.get('/users', handler)`	• Registers HTTP GET route with handler function • most concise syntax for simple routes

The rest of this section is part of the full cheat sheet

Table 3: Request Object Properties

The request object is how a handler reads everything the client sent — parsed body, params, query string, headers — plus useful derived values like the client IP, protocol, and a per-request logger. A handful of these (request.ip, request.protocol, request.hostname) only return trustworthy values once trustProxy is configured for your deployment.

Property	Example	Description
request.body	`const { name } = request.body`	• Parsed request body based on Content-Type • available after preParsing hook completes

The rest of this section is part of the full cheat sheet

Table 4: Reply Object Methods

Where request reads input, reply writes the response — setting status codes, headers, and content type, then sending a payload that Fastify serializes against your schema. Most methods chain fluently (reply.code(201).send(data)), and the escape hatches at the bottom (reply.hijack, reply.raw) hand you the raw Node response when you need to bypass Fastify's reply machinery entirely.

Method	Example	Description
reply.send	`reply.send({ status: 'ok' })`	• Sends response payload • automatically serializes using JSON Schema or JSON.stringify

The rest of this section is part of the full cheat sheet

Table 1: Server Initialization and Configuration

Option	Example	Description
logger	`fastify({ logger: true })`	• Enables Pino logger with default 'info' level • accepts boolean or config object with level, stream, and serializers
bodyLimit	`fastify({ bodyLimit: 2097152 })`	• Sets maximum request body size in bytes • defaults to 1048576 (1 MiB) to prevent memory exhaustion
trustProxy	`fastify({ trustProxy: true })`	• Enables proxied headers like X-Forwarded-For • required for accurate client IP behind load balancers or reverse proxies
ignoreTrailingSlash	`fastify({ ignoreTrailingSlash: true })`	• Treats `/users` and `/users/` as same route • simplifies routing logic by normalizing URL patterns
caseSensitive	`fastify({ caseSensitive: false })`	• Makes route paths case-insensitive • treats `/Users` and `/users` as identical routes
requestIdHeader	`fastify({ requestIdHeader: 'x-request-id' })`	• Reads existing request ID from header • useful for distributed tracing across microservices
genReqId	`genReqId: (req) => uuid()`	• Custom request ID generator function • defaults to auto-incrementing number for each instance
connectionTimeout	`fastify({ connectionTimeout: 30000 })`	• Sets idle connection timeout in milliseconds • defaults to 0 (no timeout) for HTTP/1.1
keepAliveTimeout	`fastify({ keepAliveTimeout: 72000 })`	• Sets keep-alive timeout for reusing connections • defaults to 72 seconds to match Node.js behavior
maxParamLength	`fastify({ maxParamLength: 200 })`	• Limits URL parameter length • defaults to 100 characters to prevent abuse
http2	`fastify({ http2: true })`	• Enables HTTP/2 server with multiplexing and header compression • requires Node.js 8.8+
https	`https: { key, cert }`	• Provides TLS credentials for HTTPS server • accepts key and cert file contents or paths

Table 2: Route Definition Methods

Method	Example	Description
shorthand GET	`fastify.get('/users', handler)`	• Registers HTTP GET route with handler function • most concise syntax for simple routes

Table 3: Request Object Properties

Property	Example	Description
request.body	`const { name } = request.body`	• Parsed request body based on Content-Type • available after preParsing hook completes

Table 4: Reply Object Methods

Method	Example	Description
reply.send	`reply.send({ status: 'ok' })`	• Sends response payload • automatically serializes using JSON Schema or JSON.stringify