Daily Sudoku

How one board reaches everybody without being stored

A generator that shuffles randomly produces a different puzzle every time it runs. Feed it a fixed starting number instead and it becomes completely predictable: the same sequence of shuffles, the same grid, every run. The number used here is today’s date written out as year, month and day run together, so a date in August 2026 becomes an eight-digit integer. That integer is pushed through a small shift-and-mix routine that turns it into a stream of pseudo-random values, and the generator uses that stream to build the board. Two people on opposite sides of the world get identical grids because they did identical arithmetic, not because anything travelled between them.

It turns over at midnight UTC, not at yours

The date is read in Coordinated Universal Time, so the board changes at the same instant everywhere rather than rolling around the world with the clocks. In Britain that is midnight or one in the morning depending on the season. Across the Americas it means the next day’s puzzle appears during the afternoon or evening of the day before, and in Australia and New Zealand it arrives during the morning or around midday. If you play at a consistent hour this matters exactly once, when you notice the puzzle has changed earlier than you expected.

New puzzle gives up the date

Worth knowing before you press it. The button clears the seed as well as the board, so what you get back is an ordinary random grid, not that day’s shared one – and there is no way back to the dated board except reloading the page, which restores it exactly as it was drawn. That is a fair trade if you have finished the day’s puzzle and want another, and an unwelcome surprise if you meant to restart the one you were on. Reload rather than press it.

Nothing is counting your streak

The reason most dated puzzles want you signed in is the streak. Doing a sudoku daily is a habit, and a counter is the cheapest way to sell the habit back to the person who already has it. There is no sign-in here, no record of yesterday and nothing written to your device, so a run of days exists only if you are keeping it yourself, and the daily sudoku here has no opinion about whether you played yesterday. The same absence means a half-finished grid does not survive a reload – and reloading is also the only way back to the day’s board, so it is a genuine choice. The timer in the corner starts when the grid appears and stops when the last cell is correct; it is not submitted anywhere.

Some days the board is not a medium

This page asks for a middling puzzle and the generator gets twelve attempts at one: build a full grid, take digits out one at a time while the answer stays the only answer, grade whatever is left standing, and throw the whole thing away and begin again if the grade came out wrong. If none of the twelve lands on medium it hands over whichever attempt came closest, and the badge above the grid names what the board actually earned rather than what was requested. On any other page that is a private disappointment. Here it is not, because the twelve attempts are driven by the date and therefore run identically in every browser that asks: a day that comes out hard comes out hard for everybody, and if the badge disagrees with the word medium, nobody solving today has been handed an easier grid than you have.