jsmad : jsmad is a pure javascript MP3 decoder, based on libmad, with an ID3 decoder written from scratch.
Quicktype : Quicktype generates types and helper code for reading JSON in C#, Swift, JavaScript, Flow, Python, TypeScript, Go, Rust, Objective-C, Kotlin, C++ and ...
JSHint : This is JSHint, a tool that helps to detect errors and potential problems in your JavaScript code.
jsfx : This is a javascript library (with frontend) for sound effect generation.
Online javascript beautifier : Beautify, unpack or deobfuscate JavaScript and HTML, make JSON/JSONP readable, etc.