The idea is smart and the presentation is top-notch!
From seeing the first screen and "tweaking code" to set my name and settings I've got my expectations a bit too high and wanted to do something with that part of screen during the actual puzzles. Want more puzzles that require changing rules to solve!
Little touches: screen between puzzles can be a bit longer to see what's written in the popup, the end of run should also be clearer, I ended up starting new and realized it only after solving a few again.
I am personally not a fan of speedrun-leaderboard, but this one is very cleverly done!