Ruby/WASM empowers Rubyists to build flexible applications directly on the browser. I developed "purified-synth," a browser-based synthesizer and sequencer combining Ruby/WASM with the Web Audio API. The core distinction of this project is its focus on "Pure Intonation" rather than the standard 12-tone equal temperament. While microtonal music often relies on approximations like 53-TET, this sequencer uses Ruby to calculate precise frequency ratios, enabling chords in their purest mathematical form. In this session, I will demonstrate the implementation of this musical theory in Ruby and share practical techniques for building functional applications using Ruby/WASM. I will discuss the nuances of JavaScript interoperability (JS interop) and the architectural patterns required to bridge the gap between Ruby and Web APIs, providing insights for those looking to move beyond "Hello World" examples in Ruby/WASM.