Four difficulty levels plus a daily puzzle, with pencil notes and smart highlights - practice right in your browser
Basic rules: the 9×9 board is split into nine 3×3 boxes with some cells pre-filled (givens, not editable). Fill the empty cells with 1–9 so each row, column and 3×3 box contains 1–9 exactly once with no repeats. Complete it to win.
Unique solution: every board is generated by backtracking a full solution then digging cells while a solver verifies uniqueness (stopping at a second solution), so there is exactly one answer — no multi-solution or unsolvable puzzles, letting you reason instead of guess.
Four difficulties: easy to expert differ mainly by how many cells are given — fewer givens means more reasoning steps and higher difficulty. Difficulty is an approximate casual grading, not a strict technique-tier rating.
Notes, hints and mistakes: notes mark small candidates in a cell and can auto-clear from related cells after you place a digit; with auto-check on, a digit that differs from the solution turns red and counts a mistake. An optional 3-mistake fail mode is off by default. Wins using hints or with mistakes don't count toward the clean best time.
Scores and daily puzzle: time is the core score, and each difficulty's best time only records clean solves (0 hints, 0 mistakes). The daily puzzle is generated deterministically from the date so everyone plays the same board, with a check-in streak. Progress, best times and check-ins live only in your browser, auto-resuming on refresh, no login needed.
⚠️ Every puzzle here is generated on the fly and verified to have a unique solution; it is for casual play, and time ratings are for fun, not a competitive standard.
Last updated: 2026-07-20 · Saved on this device only
