Snyder Notation
Snyder notation is a tidier way to keep pencil marks, popularised by Thomas Snyder — a world Sudoku champion — and widely used on channels like Cracking the Cryptic. Instead of writing every candidate in every cell, you mark a digit only where it really matters. The result is a far cleaner grid in which hidden singles and pairs almost announce themselves.
The idea
Full pencil marks quickly turn a grid into a wall of tiny numbers. Snyder notation cuts through that with one rule: for each digit, in each box, only pencil it in if it can go in exactly two cells of that box. Digits that can still go in three or more cells you leave off entirely for now.
Why two? Because two-candidate placements are exactly what the most useful techniques feed on. If a digit is marked in only one cell of a box, that's a hidden single — place it. If two digits are marked in the same two cells, that's a hidden pair. Both leap out when the clutter is gone.
Only the two indigo cells can still hold a 4 in this box, so that's the only place you note it. If a third cell freed up, you'd drop the mark until it narrowed to two again.
How to use it
- Go digit by digit, box by box. For each, count the cells where it can still go.
- Mark only the twos. Exactly two cells → pencil the digit in both. One → place it. Three or more → skip it.
- Watch the pairs align. When two of your marked digits land in the same two cells, you've found a hidden pair.
- Update as you go. Every placement can turn a "three or more" into a clean two — re-mark as the grid tightens.
When to switch to full marks
Snyder notation is brilliant for the early and middle game, where it keeps you fast and clear. On the hardest grids — where you need patterns like the X-Wing or Unique Rectangle — you'll eventually want full candidate lists. Many strong solvers start in Snyder and fill in the rest only once they stall.
Common mistakes
- Marking threes "just in case". The whole point is restraint — three-cell candidates are noise at this stage.
- Forgetting to re-check after a placement. A single fill can drop a digit to two cells in a box; that's a new mark to make.
- Mixing it with full marks halfway. Pick one system per grid until you're fluent, or you'll lose track of what's noted.
Which Sudoku types is this best for?
The same logic applies across variants, but it pays off more in some than others.