Fasthttp is a high-performance HTTP/1.1 server and client library for Go, designed as a drop-in replacement for the standard `net/http` package with significantly lower latency and memory allocations. It achieves this through extensive use of `sync.Pool` for object reuse, zero-allocation byte-to-string conversions (`b2s`/`s2b`), stackless goroutine wrappers for compression, and a custom worker pool that keeps CPU caches hot. The library handles both server and client roles, supporting TLS, keep-alive, pipelining, load balancing (via `LBClient`), transparent retries, and streaming request/response bodies. It also provides a rich set of sub-packages for proxy dialing (`fasthttpproxy`), `net/http` adapter (`fasthttpadaptor`), listener reuse (`reuseport`, `tcplisten`), in-memory testing utilities (`fasthttputil`), and prefork process management for multi-core deployments. The architecture is modular: core types (`Server`, `Client`, `HostClient`, `RequestCtx`, `Request`, `Response`, `Headers`, `URI`, `Cookie`, `Args`) are in the root package, while optional features live in sub-packages. The server uses an event-driven, non-blocking I/O model with a worker pool that reuses goroutines and allocates few objects per request. The client maintains connection pools with idle timeout and supports both FIFO and LIFO connection reuse to minimize latency. Extensive test coverage, including fuzz tests and allocation benchmarks, validates correctness and performance across edge cases and shared-nothing concurrency. Fasthttp is production-hardened, powering services like VertaMedia at over 200K requests per second per server with 1.5M concurrent keep-alive connections. It is not a generic web framework but a foundational layer that can be embedded into frameworks (including gin, echo, etc.) via adapters. The codebase demonstrates advanced Go patterns for high-performance I/O, making it a reference for engineers building latency-sensitive network services.