Expert Sudoku

The toughest boards we generate: few given numbers, no easy footholds, and only advanced logic to see you through. Every puzzle still has a single, guess-free solution.

The idea of expert play

Expert Sudoku hands you the bare minimum of starting clues. There are almost no cells early on where a single number is obviously forced, so you cannot lean on scanning or simple singles for long. Instead you build the solution the way an expert does, from a full grid of pencil notes and the relationships between them. This is Sudoku at its most rewarding, where a single small deduction can cascade into a dozen placements, and where finishing a board feels genuinely earned.

The rules have not changed

The three rules are the same as ever: 1 to 9 in every row, column and 3×3 box, with nothing repeated. What changes is how much work each number costs. Complete, accurate pencil notes are not optional at this level. They are the game.

Techniques that pay off

• Naked pairs and triples. When two cells in a unit share the same two candidates, those numbers belong to those cells and can be cleared from the rest of the unit. The same idea extends to three cells sharing three candidates.
• Hidden pairs. When two numbers can only go in the same two cells of a unit, every other candidate can be stripped from those two cells, even if they looked crowded.
• Pointing pairs. If a candidate within a box is confined to a single row or column, it can be removed from that same line everywhere outside the box.
• Patience. Expert boards reward slow, careful chains of reasoning. Use undo freely, follow one idea at a time, and let each elimination set up the next.

How to approach a board

Begin by penciling every candidate into every empty cell. Then hunt for the eliminating patterns above, starting with the simplest. Each pattern you spot removes candidates, which in turn creates new singles, which reveal more of the grid. The trick is to trust the process: on an expert puzzle you often make no visible progress for a while, then one deduction opens the floodgates. Keep a steady rhythm, and remember that even the hardest board is really just a long sequence of small, certain steps stitched together.

Never guess, even here

It is tempting on a hard board to place a number on a hunch and see what happens, but resist it. Every puzzle on this site has exactly one solution reachable by pure logic, so a guess is never necessary, and a single wrong one can send you down a long false path that is painful to unwind. When you feel stuck, the answer is almost always a technique you have not applied yet, or a candidate you forgot to eliminate. Slow down, recheck your notes unit by unit, and look for the smallest possible deduction rather than the biggest. The break you need is usually one careful elimination away.

Built for serious solving

Pencil notes, hints, undo and redo, a pause button and a solve timer are all here, along with a Stats screen that tracks your best times so you can measure yourself against your own record. Every board is generated fresh with a guaranteed unique solution.

Mix it up

Need a breather? Drop back to Medium or Easy. Want a harder kind of puzzle rather than a harder board? Killer Sudoku adds arithmetic cages on top of the classic rules, and Flower Sudoku reshapes the regions into jigsaw petals. The classic grid is always at Sudoku AZ.