Thanks to Jason Siefken, the new math-expressions playground is live now! math-expressions playground — Rust vs JS (The math-expressions library is what powers the <math> and <boolean> tags.)
If anyone feels like experimenting, let me or Jason know what features should be added. The old math-expressions JS code is being ported to Rust (with the help of Claude), which should allow a lot more features (as well as better simplification algorithms!)