Numeral.js is a mature, standalone JavaScript library for formatting and manipulating numbers. It provides a plugin-based architecture where number formats (e.g., currency, percentage, bytes, time) and locale definitions are registered separately, allowing extensibility and customization. The core library parses numeric strings, applies locale-specific delimiters and abbreviations, and outputs formatted strings. It also supports arithmetic operations with floating-point correction. The library is distributed as a single-file UMD module and has no external runtime dependencies. It is widely used in web applications for displaying numbers in a human-readable, locale-aware manner.