How does Ruby run in a browser?

CRuby compiled to WebAssembly (ruby.wasm). First Run downloads the VM (~12 MB); later runs use the browser cache.

No. The CDN fetch is the interpreter binary. Your source stays in this tab.

No. Only what the stdlib WASM build includes. Nokogiri and native gems will not load.

Why is the first Run slow?

The WASM module has to download and compile once. After that, eval is typically well under a second.

CRuby compiled to WebAssembly runs in your tab. The VM downloads on first Run; your source never uploads.

First Run downloads the Ruby WASM VM (~12 MB), then caches it.

Output appears here after Run.

Ruby Playground runs entirely in your browser on DevTools — no signup, no upload.

Ruby Playground is a free in-browser utility, not a hosted API, and keeps no server-side history.

Using Ruby Playground
Open Ruby Playground, enter or paste your input, and copy the result.

Track subscriptions, memberships and recurring bills on a private paid/skipped calendar.

Track supplements by meal, empty or with food, and mark taken or skipped on a private calendar.

Write JavaScript, press Run, and read console output in your browser.

Compile TypeScript to JavaScript in your tab and inspect console output.

Write Dart, press Run, and see print output in your browser.

Life Path, Destiny, Soul Urge and Personality numbers from a birth name and date.