Sudoku

Somewhere around the third empty row, the easy candidates run out and Sudoku actually starts asking something of you. That's the moment worth chasing: staring at a 3x3 square, ruling out numbers one by one, until the last digit you need is the only one left that fits.

The grid itself is simple to describe and stubborn to solve - 81 cells, nine rows, nine columns, nine boxes, and every digit from 1 to 9 allowed exactly once in each. Click a cell, click the number you think belongs, and if you're not sure yet, hit Notes and jot down the candidates without locking anything in.

Multiple difficulty levels mean you can start gentle and work up to the boards that punish a careless click. It's the kind of quiet, one-track focus that fits alongside other Puzzle games on the site, or as a change of pace from something like Mahjong Connect when you want numbers instead of tiles.

No download, no account, just a grid and your own patience. Free to play right in the browser, on desktop or mobile, whenever ten minutes opens up.

Fill every empty cell so each row, each column, and each 3x3 box contains the digits 1 to 9 with no repeats.

Click on a cell to select it, then click the number you want to place there. If you're not ready to commit, tap the Notes button first to pencil in possible numbers for that cell without actually placing them.

Pick a difficulty level that matches your mood. Watch for mistakes as you go - an early wrong guess has a way of blocking an entire row later on, so double-check a square before you lock in a number you're unsure about.