We use KaTeX for https://cocalc.com https://cocalc.com (source here https://github.com/sagemathinc/cocalc https://github.com/sagemathinc/cocalc) because it is d

We use KaTeX for https://cocalc.com https://cocalc.com (source here https://github.com/sagemathinc/cocalc https://github.com/sagemathinc/cocalc) because it is dramatically faster than MathJax. When KaTeX fails due to an error (e.g., something missing) our code falls back to MathJax, so we still get full MathJax support when needed, but with all the benefits of KaTeX. The code that John Jeng and I wrote to do this is tangled up with the rest of cocalc's code; I hope somebody else writes a standalone library that accomplishes that same thing. It wasn't too difficult to write this, though a couple of subtle issues arose in production, which we had to sort out.