Servant is a Haskell library family for defining type-safe web APIs at the type level using DataKinds, TypeOperators, and type families. The core package (`servant`) provides combinators like `:>`, `:<|>`, `Capture`, `QueryParam`, `ReqBody`, and `Verb` to describe API structure. From these type-level descriptions, the ecosystem automatically derives server implementations (`servant-server`), client functions (`servant-client`, `servant-http-streams`), documentation (`servant-docs`), OpenAPI/Swagger specs (`servant-openapi3`, `servant-swagger`), and property-based tests (`servant-quickcheck`). The architecture is modular: each sub-package interprets the same API type via typeclasses (`HasServer`, `HasClient`, `HasDocs`, `HasSwagger`, `HasOpenApi`), enabling a single source of truth for the API contract. The server package provides a WAI `Application` via `serve` and `serveWithContext`, supporting custom monads, authentication (JWT, cookies, basic auth via `servant-auth`), streaming (conduit, pipes, machines), and error handling with configurable formatters. The client package generates type-safe query functions that run in a `ClientM` monad over HTTP. The ecosystem also includes foreign language bindings (`servant-foreign`), generic record-based APIs (`NamedRoutes`), and a rich set of cookbook examples covering real-world patterns like pagination, file upload, Prometheus metrics, and OpenID Connect. Key external dependencies include `warp` (server), `http-client`/`http-streams` (client), `aeson` (JSON), `jose` (JWT), `swagger2`/`openapi3` (spec generation), and `QuickCheck` (testing). The codebase is heavily tested with CI across multiple GHC versions (9.2–9.14) and uses Nix for reproducible development environments. While the type-level machinery can produce cryptic errors, the library is production-grade and widely used in the Haskell ecosystem.