Greater Than Sudoku

A Sudoku you solve from comparisons. Between neighbouring cells inside each 3×3 box sits a < or > sign, and with only a few given numbers you deduce the whole grid from those inequalities and the usual rules. Also known as Comparison or Less Than Sudoku. Free, in your browser, in three levels.

How it works

The board is an ordinary 9×9: every row, every column and every 3×3 box must contain the numbers 1 to 9 exactly once. What changes is where the clues come from. Instead of a grid full of given digits, almost every pair of side-by-side cells within a box carries a sign — and the open side of the sign always points at the larger number. So 5 > 2 and 3 < 7. Read the signs together with the Sudoku rules and each cell is forced, one deduction at a time.

Reading the signs

Take any run of cells in a box. A chain like 2 < 5 > 4 tells you the middle number is the biggest of the three, and the ends are smaller. Corners and edges where several signs meet are the best place to start: a cell that must be greater than two neighbours and less than none can only be a high number, and the reverse pins the low ones. As you place numbers, the normal row, column and box eliminations do the rest.

Tips for your first game

• Find the extremes first: a cell every sign points away from is a 9; a cell every sign points toward is a 1.
• Follow the sign chains inside a box — they order several cells at once.
• Then switch to ordinary Sudoku scanning to lock the rest.
• A wrong entry turns red — including when it breaks a < or > sign, not just a duplicate.

Everything you expect

• Three difficulty levels — from a friendly start with more givens to a stern board with only a handful.
• Undo, erase, a one-cell hint and Show solution, a solve timer and a mistakes counter.
• Your progress is saved automatically, and the game follows the site's light or dark theme.

A worked example

Suppose a short run inside one box reads cell A < cell B > cell C, and a fourth sign tells you C > D. Straight away B is the largest of the group and D is the smallest, with A and C somewhere in between. If the box already contains a 9 elsewhere, B cannot be 9, which caps the whole chain and often forces D down to 1 or 2. None of this needs a single given digit — the ordering alone, combined with the numbers a box, row or column has already used, keeps narrowing the options until one value survives. That is the whole pleasure of the variant: you are reasoning about relationships between cells, not just which digits are missing, and the grid unlocks in satisfying cascades once the first few extremes fall into place.

Where it comes from

Greater Than Sudoku grew out of the same family as Futoshiki, the Japanese "inequality" puzzle, but keeps the full 9×9 grid with its 3×3 boxes rather than a plain Latin square. That combination is what makes it feel familiar and fresh at once: all your ordinary Sudoku instincts still apply, yet the clues arrive as comparisons instead of printed numbers. If you have never solved from inequalities before, start on the easy level, where a few given digits give your chains something to anchor to.

More logic variants

If you like an extra rule layered on Sudoku, try Killer Sudoku (arithmetic cages) or Diagonal Sudoku (Sudoku X). Prefer a calmer, more visual solve? Color Sudoku swaps numbers for colours. The pure original is always a tap away at Sudoku AZ, with a real test on Expert Sudoku.