# Introduction

tsoa is a framework with integrated OpenAPI compiler to build Node.js serve-side applications using TypeScript. It can target express, hapi, koa and more frameworks at runtime. tsoa applications are type-safe by default and handle runtime validation seamlessly.

# Goal

  • TypeScript controllers and models as the single source of truth for your API
  • A valid OpenAPI (formerly Swagger) spec (2.0 or 3.0) is generated from your controllers and models, including:
    • Paths (e.g. GET /Users)
    • Definitions based on TypeScript interfaces (models)
    • Parameters/model properties marked as required or optional based on TypeScript (e.g. myProperty?: string is optional in the OpenAPI spec)
    • jsDoc supported for object descriptions (most other metadata can be inferred from TypeScript types)
  • Routes are generated for middleware of choice
    • Express, Hapi, and Koa currently supported, other middleware can be supported using a simple handlebars template
    • Seamless runtime validation

# Philosophy

  • Rely on TypeScript type annotations to generate API metadata if possible
  • If regular type annotations aren't an appropriate way to express metadata, use decorators
  • Use jsdoc for pure text metadata (e.g. endpoint descriptions)
  • Minimize boilerplate
  • Models are best represented by interfaces (pure data structures), but can also be represented by classes
  • Runtime validation of tsoa should behave as closely as possible to the specifications that the generated OpenAPI 2/3 schema describes. Any differences in validation logic are clarified by logging warnings during the generation of the OpenAPI Specification (OAS) and/or the routes.
    • Please note that by enabling OpenAPI 3 you minimize the chances of divergent validation logic since OpenAPI 3 has a more expressive schema syntax.