Daily Sudoku

The puzzles come from a stored pool of 60 per level, and the rules are exactly those of classic Sudoku.

What makes a puzzle “the daily”?

Everyone who opens this page on the same UTC date gets the same puzzle, in the same orientation, with the same digits. The new puzzle appears at midnight UTC, which is a different local time depending on where you are. There is no New button on this board, because a second puzzle would not be the daily. You can restart the one you are on, and pause it. Everything else about play is covered by the rules and controls pages.

Which level is each day?

The schedule is stored in the site’s code and the page reads it from there. It starts the week gently on Monday, builds through Thursday, and puts the two hardest kinds on the weekend. The level names follow the site’s own grading, explained in how Sudoku difficulty is graded.

How is the puzzle chosen?

The server combines the UTC date, the level for that weekday and a secret value called a salt, and turns them into a number with a standard hash function. That number selects one puzzle from the level’s pool of 60. A second number, derived the same way, seeds a transformation that relabels the digits and shuffles rows, columns and bands in ways that keep the puzzle valid, unique and equally hard. Because the salt stays on the server and is not in the public code, nobody can work out future puzzles from the repository.

The honest consequence is that the pool is finite. The pick is a hash and not a rotation, so it is possible for the same underlying puzzle to come round again on another date, in a different disguise. Transformations change how a puzzle looks, but not its logic, and a solver with a good memory for structure might recognize one. The site does not claim every daily is a brand-new puzzle.

What is in the pool?

The daily pool has 60 puzzles at each of the five levels, 300 in all, and every one is verified to have exactly one solution. Givens run from 22 to 29. From the technique data for this pool:

• Easy (Monday): naked singles in all 60 puzzles and hidden singles in 97%.
• Medium (Tuesday, Wednesday): pointing pairs in 98%, box/line reduction in 35% and naked pairs in 32%.
• Hard (Thursday): naked triples in 63% and X-Wing in 37%.
• Expert (Friday, Saturday): XY-Wing in 75% and simple coloring in 43%.
• Evil (Sunday): every puzzle needs a unique rectangle.

With 60 samples per level these percentages are rough, and the larger classic pool in the technique frequency guide is the better reference. They do tell you what to expect on a given weekday. Sunday is the day to have the unique rectangles lesson fresh, and Friday and Saturday reward knowing XY-Wing.

How does the streak work?

• Completing the daily on a day after you completed it the day before adds one to your streak.
• Completing it twice on the same day does not change the streak.
• If you skip a day, the next completion starts a new streak at 1. On the day you have missed, the page shows a streak of 0 until you finish again.
• Replaying a daily you have already finished is practice mode. A banner says that the replay does not change your streak or statistics.

The page also shows a calendar of the last 28 days, marking which days you completed, which you missed and today. Your streak, best streak and results live only in this browser, so they do not follow you to another device, and clearing site data removes them. Day boundaries are UTC, so a streak can break earlier or later than your own midnight suggests.

How should you approach it?

1. Check the weekday and level first. Sunday’s Evil puzzle is a different task from Monday’s Easy.
2. On Medium and above, switch notes on once the singles run out and look for pointing pairs before anything heavier. The pencil marks guide helps.
3. Use hints for learning on the days you are stretching. They name the technique and are worked out from the placed digits.
4. If you are short of time, pause. The game also pauses by itself when you switch apps, so a short interruption does not cost you the puzzle.

Where next?

For a no-aid version of the same puzzles, try expert mode. To practice a particular level any day, use the level chooser on the home page. The 6×6 board suits a shorter session, killer suits a change of pace, and the games hub lists every board.