This looks really promising! I just tried it out. A few pieces of feedback!

1. It seems like the save delay is a bit too long. If you reload the page within like 1s of writing, what you just wrote disappears. Maybe make that faster and/or include a confirmation that there's unsaved changes if you try to close so you don't lose changes.

2. I was expecting some of the other languages to evaluate too (specifically JS). Maybe I missed something, but it seems like just the Math blocks are evaluable? Does it work with JS too?

Some things I love: 1. Block concept! 2. It's a scratchpad, there's no files to save. I'd love to use this as a dev journal.