NestJS is a progressive framework for building server-side applications with Node.js and TypeScript. It organizes code into modules, controllers and injectable providers, and while it uses Express by default it can also run on Fastify, giving teams a consistent architecture on top of familiar HTTP foundations.
The site provides a thorough getting-started guide, documentation on providers, middleware, guards, interceptors, pipes and exception filters, plus dedicated sections for configuration, validation, caching, authentication, database integration, GraphQL, WebSockets, microservices and testing, along with an official CLI and schematics.
It suits backend teams that want a maintainable structure for medium to large APIs, developers moving from Angular or Spring who expect dependency injection and decorators, and organizations standardizing several services on one convention so new engineers can navigate any codebase quickly.
Compared with minimal Express applications it adds conventions and a steeper initial learning curve but pays off in testability and separation of concerns; compared with full-stack meta-frameworks it stays focused on the server side, leaving rendering and client routing to other tools.
Read the providers and module chapters before designing feature folders, choose the Express or Fastify adapter early since platform-specific APIs differ, and keep controllers thin so business logic stays in injectable services that can be unit tested without starting an HTTP server.