Sudoku solver
Type a grid in (or start from one you're stuck on), then validate it, solve it outright, or ask for the technique-by-technique reasoning our logical solver actually uses.
How this works
Validate checks the rules only: no digit can repeat in a row, column, or box among the cells you've entered. A grid can be valid and still be unsolvable, or solvable more than one way — that's what Solve checks next, by counting how many completions actually exist before filling one in.
Show steps runs the same technique-ordered logical solver that powers in-game hints: naked and hidden singles first, then locked candidates, pairs, triples, X-Wing, Swordfish, and XY-Wing, in that order, applying whichever is simplest at each point. If it stops before the grid is full, whatever's left needs something beyond those ten techniques — see the technique pages for how each one works.