The grid & colour language
Sudoku University uses one consistent colour language across the grid, every hint, and this handbook, so once you learn it here it applies everywhere in the game.
Given digits are printed in dark ink and can never be changed. Everything you place yourself appears in blue, so you can always tell your own work apart from the puzzle's starting clues at a glance. When a hint is active, the same blue shifts to a highlighted shade to draw your eye to the cells, rows, columns or boxes the logic is currently pointing at. If a digit conflicts with another in its row, column or box, it switches to the magenta/red error shade until you fix it.
Candidate notation modes
Candidates are the small pencil-marks in a cell showing which digits could still legally go there. Sudoku University supports three ways of keeping track of them: pick whichever matches how you like to think.
Auto notation
The game keeps every cell's full candidate list up to date for you automatically. This is the easiest way to start: you always see the complete, accurate picture of what's still possible in a cell, with no bookkeeping of your own required.
Manual notation
You take full control. The game places no candidates for you: every pencil-mark you see is one you put there yourself, and nothing is added or removed automatically as you play. This is the closest experience to solving on paper, and it rewards careful, self-directed candidate tracking.
Snyder notation
A middle ground borrowed from a well-known paper-solving convention: only candidates that appear in exactly two cells within a row, column or box get marked (the pairs that are most useful for spotting Locked Candidates and Naked/Hidden Pairs quickly). It keeps the grid far less cluttered than full Auto notation while still surfacing the marks that matter most for early-tier techniques.
Switching notation modes doesn't erase your progress. Your placed digits are always preserved, only the pencil-mark bookkeeping changes.
Which mode should I use?
New to Sudoku University? Start with Auto notation so you can focus on learning the techniques in the Technique Glossary without also having to manage candidates by hand. Once locked candidates and pairs feel natural, try Snyder notation for a lighter touch, or go full Manual if you want the complete paper-solving experience.
Using the hint system
Every hint unfolds in four steps rather than simply announcing an answer, so you can stop reading the moment you see the logic for yourself:
- Technique: the technique and its difficulty tier are named, along with a short statement of the general premise (for example, "Somewhere a cell has only one candidate left").
- Region: the row, column or box the technique is acting in is named and highlighted on the grid, narrowing down where to look.
- Targets: the specific cells and candidates are highlighted, and the resulting placement or elimination is stated directly (for example, "So 6 goes in r9c5").
- Solution: the full plain-language argument, walking through exactly why the placement or elimination holds.
You can stop at any step. Many players only ever need the first one or two once a technique becomes familiar.
Hints that depend on your own candidate notes being accurate are flagged with an amber "leaning" highlight, a signal that the suggestion trusts your pencil-marks, so it's worth double-checking them if something looks off. For Novice-tier singles, a Show All option can reveal every immediately available single at once rather than one at a time. From Medium tier upward, an optional technique picker lets you ask for a hint using a specific technique rather than whatever the engine would suggest next.
Controls & shortcuts
Standard play uses the number keys 1–9 to enter a digit into the selected cell, Shift plus a number to toggle it as a candidate instead, and the arrow keys to move the selection around the grid.
Keyboard
| 1–9 | Place the digit in the selected cell |
|---|---|
| Shift + 1–9 | Toggle that digit as a candidate in the selected cell (the keyboard form of Manual notation) |
| Arrow keys | Move the selection around the grid |
| Backspace / Delete | Clear the selected cell |
| Enter | Place the digit a visible hint has already pointed at for the selected cell |
| H | Request the next hint, or step forward through a hint's stages |
| A / S / M | Switch to Auto, Snyder, or Manual notation |
| C | Press once to turn on candidate coloring; press again to clear the current coloring; press a third time to leave the mode |
| L | Press once to turn on chain-line drawing; press again to clear the drawn lines; press a third time to leave the mode |
| Hold W while clicking a link | Draw a weak link instead of the default strong link |
| Esc | Cancel a chain line that's mid-click, or clear the current multi-cell selection |
| Ctrl/Cmd + Z | Undo |
| Ctrl/Cmd + Y (or Shift + Ctrl/Cmd + Z) | Redo |
Mouse
| Click a cell | Select it |
|---|---|
| Click and drag | Brush-select a group of cells, replacing the current selection |
| Ctrl/Cmd + click and drag | Brush-select a group of cells, adding them to the current selection |
| Shift + click a candidate | Toggle that candidate in the cell (same effect as Shift plus the digit key) |
| Alt/Option + click a candidate | Place that digit outright, regardless of the candidate's current state |
| Double-click a candidate | Write it in as the cell's answer |
| Right-click | Strikes a candidate in ordinary play; paints the second colour while coloring mode is active; draws a weak link while chain-line mode is active |
The full control scheme is still being finalized during development. Check Settings → Controls in-game for the authoritative, up-to-date list once available.
Undo, redo & compose mode
Every placement, note, and hint step can be undone and redone, so exploring a technique never risks your progress. If you'd rather solve a puzzle from a book, a newspaper, or your own design, compose mode lets you enter a starting grid by hand, either by typing digits directly onto the board or by pasting an 81-character puzzle string, before handing it back to the solver and hint engine.