Currently making a perfect sudoku webapp / plugin using native JS and html templates where I'm very enthousiast about.

It allows to select multiple cells and then put in a number and all selected have that number. It keeps state of every change, you can do unlimited redo's. Right click or double click someehere removes selection. Not built yet, but it will have a box where you can paste sudoku's you've found on the internet. I just parse 81 times [1-9] with regex. So all formats are supported including noisy ones as long the noise is not numbers. Making your own puzzle is very easy. Art is to make hard ones. I'm generating extra hard puzzles using C threading. For reference: there are 6,670,903,752,021,072,936,960 sudoku puzzles possible and from that I try to resolve the hard ones using simple human logging with brute forcing as fallback until it can use logic again. 30 million attempts to solve per secon. I should at some more logic. I don't do xwing or ywing, bs imho. You have to be a superhuman to spot xwing / ywing possibilities. I think i can imagine a better logic myself. We'll see.

And yes, that's a real screenshot. Puzzle is validated and it found issues. Marked with red font. Green is current selection by user