Play Medium Sudoku Online
The tier where notes start earning their keep: a medium Sudoku is waiting – free in your browser, no ads, no sign-up, no clock.
Medium Sudoku is where pencil notes earn their keep: our medium puzzles are generated so that pair techniques come into play, while every grid keeps exactly one solution. Play free in your browser – no ads, no sign-up – and use notes, careful scanning, and naked or hidden pairs to work through each puzzle without guessing.
The rules, briefly
Each digit 1–9 exactly once per row, column, and 3×3 box — that single constraint is the whole rulebook. Medium grids begin with 33 givens, and every puzzle we serve has exactly one solution, machine-verified before it ever reaches you. Notes mode and a quiet error hint are one tap away; there is no timer.
Strategy: the notes workflow and the power of pairs
Medium is the tier where a workflow beats raw staring:
Build notes as you scan
Do your first pass exactly as on Easy — scan, place singles. But now, whenever a cell narrows to two or three candidates, mark them. You’re not just solving; you’re building the map for the next technique.
Naked and hidden pairs
When two cells of one unit share the same two candidates, those digits are spoken for — erase them from the rest of the unit (naked pair). And when two digits, between them, fit only into the same two cells of a unit, everything else in those cells can go (hidden pair). Every medium puzzle here is generated so pair logic genuinely comes into play — that’s what the tier means on this site.
Let eliminations cascade
A pair rarely solves a cell directly; it removes candidates until a new single appears somewhere else. Follow that chain calmly and the grid unravels. When pairs feel natural, Hard adds box-line interactions and triples — or return to the Sudoku overview any time.
Frequently asked questions
What separates medium from easy Sudoku?
Fewer givens (33 instead of 39) and, more importantly, deeper deductions: our medium puzzles are generated so that singles alone stall somewhere and pair techniques become necessary. Each puzzle is machine-checked to sit exactly in that band.
Do I really need pencil notes on medium?
Strictly speaking no – some solvers keep candidates in their head – but notes are what pair techniques are made of. Marking two-candidate cells as you go turns pairs from invisible into obvious.
What is a naked pair, in one sentence?
Two cells in the same row, column, or box that share the same two candidates – so those two digits belong to those two cells, and you can erase them from every other cell of that unit.
I'm stuck mid-puzzle – what now?
Re-scan with fresh eyes for a missed single, then check your notes for a pair you haven't exploited. Medium puzzles never require anything beyond that band – it's always there to find, no guessing needed.