Puzzle format
The sudoku-puzzle file: the format, every rule family, complete examples and a quick reference.
Grade card
The sudoku-grade format: every field of a grade card (difficulty, time, band, techniques, steps, issues).
Generator spec
The sudoku-spec format: a request to the puzzle generator (board, rules, givens, symmetry, targets).
Other formats
Reading and writing other sudoku formats: plain strings, text grids, sudokuwiki.org strings and ipuz.