Five techniques worth knowing well — scanning, pencil marks, naked pairs, hidden pairs, and pointing pairs — are enough to solve Noodler Sudoku's daily hard grid without ever needing to guess.
Sudoku's deceptively simple to explain and properly hard to do well. Every grid has exactly one solution, and you never need to guess - if you're stuck, it's because there's a technique you haven't spotted yet, not because you're missing information.
A few that'll get you through most grids:
1. Scanning
The most basic technique, and the one everyone starts with. Look at a row, column, or box and work out which numbers are missing, then check which cells could actually hold each one based on what's already in their row and column.
2. Pencil marks
If you're not writing small candidate numbers in the corners of empty cells, start. It's the difference between holding six possibilities in your head and just being able to see them. Once a cell's down to one candidate, it's solved.
3. Naked pairs
If two cells in the same row, column, or box both have exactly the same two candidates left (say, both can only be 4 or 7), those two numbers are locked to those two cells. You can safely remove 4 and 7 as candidates everywhere else in that row, column, or box.
4. Hidden pairs
The reverse of the above. If two numbers only appear as candidates in the same two cells anywhere in a row, column, or box, those cells must be those two numbers - even if they've still got other candidates pencilled in. Strip the rest out.
5. Pointing pairs
If a candidate number only appears in one row or column within a box, it has to go somewhere in that row or column inside the box. So you can rule it out everywhere else in that row or column outside the box.
6. If you get stuck
Most "hard" grids need at least one of the pair techniques to crack - scanning alone won't get you there. But you shouldn't need anything more advanced than what's above; the difficulty is deliberately calibrated so a solid grasp of these five gets you through.
If you get properly stuck, the elimination logic is always there in the grid somewhere. It's just a case of looking more carefully.
Frequently asked questions
What is Noodler Sudoku?
Noodler Sudoku is a free daily hard Sudoku grid, generated fresh each day with no repeats.
Do I ever need to guess in Sudoku?
No. Every valid Sudoku puzzle, including Noodler's daily grid, has exactly one solution reachable through logical elimination alone — if you're stuck, there's a technique to find, not a guess to make.
What's the difference between naked pairs and hidden pairs?
A naked pair is two cells that each have only the same two candidates left; a hidden pair is two candidates that only appear in the same two cells, even if those cells still have other candidates pencilled in. Both let you eliminate candidates elsewhere.
Do I need pencil marks to solve Sudoku?
You don't strictly need them, but pair-based techniques are far harder to spot without pencilling in candidates first — it turns six possibilities held in your head into something you can actually compare side by side.
Can I replay old Noodler Sudoku puzzles?
Yes — the Past Sudoku archive lets you revisit earlier grids, and they stay fully playable.
Ready to put these to work? Play today's Sudoku or try an archived grid at your own pace.