Sudoku Next Move Finder (Naked Single)

You are stuck on a sudoku and you do not want the full solution, just the next cell so you can keep going on your own. That is what happens here: you paste the board as a single 81-character line, read left to right and top to bottom, using a dot or a zero for empty cells. What comes back is one move, given as a row, a column and the digit that belongs there.

Under the hood this is the simplest sudoku technique, the naked single: for every empty cell the tool collects the digits already present in its row, its column and its 3x3 box, and if exactly one digit from 1 to 9 survives, that is the move. It scans in reading order and stops at the first cell it finds, so the suggestion is not the easiest or the best one, just the first. Hidden singles are not covered.

The workflow is iterative: play the suggested move, update your 81-character line and paste it again for the next one. If the answer says there is no single candidate, either the puzzle needs a more advanced technique or you mistyped the board. Double-check the grid first, because nothing is validated here: two 5s in the same row raise no warning and a move may still be suggested. The whole thing runs in your browser.