FastestSmallestTextEncoderDecoder is a tiny, high‑performance JavaScript polyfill that implements the UTF‑8‑only parts of the Web API `TextEncoder`, `TextEncoder.encodeInto` and `TextDecoder`. It can be used in browsers (including old ones), Node JS, Workers and module systems, and is distributed via npm or a single minified script for easy inclusion. The library is aimed at developers who need reliable, fast string‑↔ Uint8Array conversion where native support is missing or inconsistent.