{sudoku} draws a sudoku as an HTML table with the three-by-three boxes marked. The puzzle is written as its 81 cells, row by row: a digit for a given, a . or 0 for an open cell. Whitespace is passed over, as are the bars and plus signs of a grid drawn in text, so the puzzle may be written as one string or as nine lines.

Without options the givens show in bold and the open cells are empty - ready to print. An open cell says "empty" to a screen reader. With solve a backtracking solver fills in every open cell, in another colour than the givens. It tries the cell with the fewest candidates first, so even the hardest published puzzles are solved well within a second. title= adds a caption.

Under the strict check a wrong number of cells, an unknown character, two equal givens in a row, column or box, and - with solve - a puzzle that has no solution are errors. The colours are --pad-sudoku-line, -box, -given, -solved, -cell and -shade on .pad-sudoku.