Axios is a promise-based HTTP client for both browser and Node.js environments. It provides a rich feature set including request/response interceptors, automatic JSON serialization, cancellation via AbortController or legacy CancelToken, progress tracking, CSRF protection, and support for multiple adapters (XHR, HTTP, Fetch). The library is designed with a modular architecture: core classes (Axios, AxiosError, AxiosHeaders, InterceptorManager) handle request lifecycle and configuration merging, while platform-specific adapters handle actual network I/O. A comprehensive set of helper utilities (composeSignals, progressEventReducer, sanitizeHeaderValue, etc.) implement reusable patterns for signal composition, throttled progress events, header injection prevention, and more. The codebase is extensively tested across runtimes (Node, browser, Bun, Deno) and includes security hardening against prototype pollution, SSRF, and CRLF injection. While primarily a library for other applications, its architecture demonstrates strong separation of concerns and many components are independently reusable.