What’s tougher about Hard?
Hard puzzles have no givens at all — you start with a totally empty grid full of cages. Cages can have up to five cells, so the totals get bigger and the combos get trickier.
You’ll need to use multiple strategies together. Don’t rush! Most Hard puzzles take 18–30 minutes when you’re used to them, and longer when you’re still learning.
If you haven’t played the easier levels yet, do a few rounds at Medium Killer Sudoku first to make sure the basic strategies (single combos, 45 rule, locked pairs) feel automatic. Hard relies on all of them at the same time.
Two real solver tricks
-
Naked pairs across cages
If two cells in a row both can only be 3 or 5 (because of their cages), no other cell in that row can be 3 or 5. Erase them from your notes.
-
Killer pair sums
A 3-cell cage totaling 6 can only be 1+2+3 (any other combo repeats or goes over). Once you spot the combo, you’ve narrowed those cells massively.
Hard puzzle game plan
-
Step 1
Tap Auto Notes to fill all the candidate numbers.
-
Step 2
Find any cage with one possible combo and lock it in.
-
Step 3
Apply the 45 rule on every box — missing pieces often pop out.
-
Step 4
Look for naked pairs to clean up your notes.
-
Step 5
When stuck, tap Hint — then keep going!
Common Hard mistakes
- ⏩ Going too fast. Hard punishes a quick guess — wrong numbers ripple through cages and rows.
- 📝 Forgetting to update notes after a placement. Always erase the new digit from neighbours’ notes.
- 🔢 Only using row/column/box logic. The cages give you extra clues — use them.
- ✅ Skipping the Check button. If something feels stuck, the most likely reason is a wrong digit from earlier.
Frequently asked questions
Is Hard too tough for kids?
Hard is really meant for kids who’ve already played a lot of regular sudoku and a few Easy/Medium Killer puzzles. If it feels too tough, jump back to Medium — there’s no rush.
Can I solve a Hard puzzle without guessing?
Yes — every puzzle on this site has exactly one solution and is designed to be solved with logic. If you’re stuck, the Hint button always reveals a correct cell.
How does Hard Killer compare to Hard 9×9?
They’re different challenges. Hard 9×9 is all about pattern-spotting; Hard Killer adds the cage sums on top. If you can do one, you can usually pick up the other within a few sessions.
Try other sudoku games
Different rules, same friendly board. Pick a sibling puzzle to play next.