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Fastify

Overview

Fastify is a high-performance, low-overhead web framework for Node.js built on a plugin-first architecture. It emphasizes JSON Schema validation, a deterministic request-reply lifecycle, and encapsulation by default. An agent needs to know it to build scalable APIs and navigate its hook-driven plugin system.

Mental Model

Fastify treats every feature as a plugin, forming a tree of encapsulated contexts where decorators extend functionality and hooks intercept the request-reply lifecycle. The framework relies on zero-cost abstractions, strict JSON Schema validation, and a deterministic plugin loading order. Canonical pages: fastify/docs/latest/Guides/Getting-Started/index.md, fastify/docs/latest/Guides/Plugins-Guide/index.md, fastify/docs/latest/Reference/Hooks/index.md, fastify/docs/latest/Reference/Lifecycle/index.md.

Learning Paths

  • New Developer: fastify/docs/latest/Guides/Getting-Started/index.md → fastify/docs/latest/Guides/Plugins-Guide/index.md → fastify/docs/latest/Reference/Routes/index.md
  • Production Engineer: fastify/docs/latest/Guides/Database/index.md → fastify/docs/latest/Reference/Validation-and-Serialization/index.md → fastify/docs/latest/Guides/Delay-Accepting-Requests/index.md → fastify/docs/latest/Guides/Benchmarking/index.md
  • Framework Contributor: fastify/docs/latest/Reference/Hooks/index.md → fastify/docs/latest/Reference/Lifecycle/index.md → fastify/docs/latest/Reference/Decorators/index.md → fastify/docs/latest/Reference/Plugins/index.md → fastify/docs/latest/Guides/Contributing/index.md

Concept Map

  • Server & Basics
    • Getting Started → fastify/docs/latest/Guides/Getting-Started/index.md
    • Routes → fastify/docs/latest/Reference/Routes/index.md
    • Request / Reply → fastify/docs/latest/Reference/Request/index.md, fastify/docs/latest/Reference/Reply/index.md
  • Plugin Architecture
    • Plugins Guide → fastify/docs/latest/Guides/Plugins-Guide/index.md
    • Encapsulation & Scope → fastify/docs/latest/Reference/Plugins/index.md
    • Decorators → fastify/docs/latest/Reference/Decorators/index.md
    • Ecosystem → fastify/docs/latest/Guides/Ecosystem/index.md
  • Lifecycle & Hooks
    • Hooks → fastify/docs/latest/Reference/Hooks/index.md
    • Lifecycle → fastify/docs/latest/Reference/Lifecycle/index.md
  • Validation & Types
    • Validation and Serialization → fastify/docs/latest/Reference/Validation-and-Serialization/index.md
    • Fluent Schema → fastify/docs/latest/Guides/Fluent-Schema/index.md
    • Type Providers → fastify/docs/latest/Reference/Type-Providers/index.md
  • Operations & Reliability
    • Benchmarking → fastify/docs/latest/Guides/Benchmarking/index.md
    • Delay Accepting Requests → fastify/docs/latest/Guides/Delay-Accepting-Requests/index.md
    • Detecting Client Abort → fastify/docs/latest/Guides/Detecting-When-Clients-Abort/index.md
    • Logging → fastify/docs/latest/Reference/Logging/index.md
  • Data & Migration
    • Database → fastify/docs/latest/Guides/Database/index.md
    • Migration Guides → fastify/docs/latest/Guides/Migration-Guide-V3/index.md, fastify/docs/latest/Guides/Migration-Guide-V4/index.md, fastify/docs/latest/Guides/Migration-Guide-V5/index.md
    • LTS → fastify/docs/latest/Reference/LTS/index.md

If You Need To...

If you need to...Read
Build your first serverfastify/docs/latest/Guides/Getting-Started/index.md
Master plugins and encapsulationfastify/docs/latest/Guides/Plugins-Guide/index.md
Intercept the request lifecyclefastify/docs/latest/Reference/Hooks/index.md
Validate requests and serialize responsesfastify/docs/latest/Reference/Validation-and-Serialization/index.md
Use TypeScript type providersfastify/docs/latest/Reference/Type-Providers/index.md
Connect to a databasefastify/docs/latest/Guides/Database/index.md
Benchmark performancefastify/docs/latest/Guides/Benchmarking/index.md
Handle client disconnectsfastify/docs/latest/Guides/Detecting-When-Clients-Abort/index.md
Delay accepting requests on startupfastify/docs/latest/Guides/Delay-Accepting-Requests/index.md
Migrate to a new major versionfastify/docs/latest/Guides/Migration-Guide-V5/index.md
Extend the Fastify instancefastify/docs/latest/Reference/Decorators/index.md
Understand the request lifecyclefastify/docs/latest/Reference/Lifecycle/index.md

Top Must-Know Pages

  1. fastify/docs/latest/Guides/Getting-Started/index.md — Install Fastify and create your first server and plugin.
  2. fastify/docs/latest/Guides/Plugins-Guide/index.md — Core guide to the plugin system, decorators, hooks, and encapsulation.
  3. fastify/docs/latest/Reference/Hooks/index.md — Complete reference for request/reply and application lifecycle hooks.
  4. fastify/docs/latest/Reference/Lifecycle/index.md — Detailed visual reference of the Fastify request/response lifecycle.
  5. fastify/docs/latest/Reference/Plugins/index.md — Deep dive into plugin registration, scope handling, and distribution.
  6. fastify/docs/latest/Reference/Validation-and-Serialization/index.md — How to validate inputs and serialize outputs with JSON Schema.
  7. fastify/docs/latest/Reference/Decorators/index.md — Extend Fastify instances and encapsulation contexts with custom functionality.
  8. fastify/docs/latest/Guides/Database/index.md — Integrate MySQL, Postgres, Redis, and MongoDB into your application.
  9. fastify/docs/latest/Guides/Benchmarking/index.md — Performance testing workflows for current branches and Node.js versions.
  10. fastify/docs/latest/Guides/Migration-Guide-V5/index.md — Latest breaking changes, LTS cycle, and V5 upgrade requirements.