81Sudoku
Log in
Sign up
81Sudoku
A free, logic-driven Sudoku platform - here's what makes it different, and answers to the questions we hear most.
Welcome to 81Sudoku.com, a free online sudoku platform designed for true puzzle enthusiasts. A classic grid consists of exactly 81 cells, but cracking the toughest ones takes more than just simple guessing. Our engine uses advanced human-style math to generate perfectly balanced grids - every puzzle here is solvable with pure logic, never trial-and-error.
Live now, with a growing set of features built to actually teach you the game, not just let you play it:
Yes. 81Sudoku is free to play, with the full feature set - hints, daily challenges, streaks, undo/redo - live and playable right now. It's a young, actively developed project, so expect it to keep improving.
Every puzzle is generated so it can be solved with pure human logic - no trial-and-error guessing required. Puzzles are rated by the specific solving techniques needed, from basic singles up to advanced tactics like X-Wing, Swordfish, and XY-Wing, powered by the HoDoKu solving engine.
Hints are tiered instead of just solving the cell for you: tap once to see which cell to look at, tap again for the full explanation naming the actual technique, and a third tap reveals the answer. An Always-On mode can also walk you through an entire puzzle step by step as a dedicated learning aid.
No account is required to play. Signing up is only needed if you want to save progress, track streaks/stats, or get notified about updates.
Yes - the Practice picker lets you choose a technique by name and serves a puzzle that genuinely needs it, and the technique library has a full explainer for each one if you want to read up first.
See Updates for what's changed recently.
Bugs, ideas, anything rough around the edges - tell us.