llhttp is a high-performance HTTP/1.1 parser written in TypeScript that generates optimized C source code via the llparse state machine compiler. It is the parser used by Node.js for handling HTTP requests and responses. The core logic is defined as a finite state machine in TypeScript, which is then compiled to C for maximum performance, achieving around 156% faster parsing than the legacy http_parser. The architecture separates the HTTP line parsing (method, URL, version) from header and chunked body parsing, with a dedicated URL state machine. The parser supports both request and response modes, configurable lenient parsing for non-compliant clients, and exposes callbacks for message begin/end, headers, body, and chunk events. It is distributed as both a native C library and a WebAssembly module, making it usable in diverse environments.