Sum Cross is a crossword made of numbers. Each white run of squares has a clue — the number it must add up to — shown in the dark square before it: across clues in the top-right corner, down clues in the bottom-left. Fill every square with a digit from 1 to 9 so each run reaches its total without repeating a digit. A helper lists the digit combinations that fit the selected runs, repeated digits turn red, and completed runs turn green. All fifteen puzzles have exactly one solution, growing from small 4×4 warm-ups to 6×6 grids.
How to play Sum Cross
Goal: Fill every white square so all across and down runs match their sums with no repeated digits.
Keyboard & mouse
- Click a white square or move with the arrow keys
- Type 1–9 to fill it; Backspace or 0 erases
- P or Escape to pause
Phone & tablet
- Tap a white square, then tap a number
- Erase clears it; Reveal cell fills it in for you
Rules
- The number in the top-right of a clue square is the total for the run to its right.
- The number in the bottom-left is the total for the run below it.
- Use digits 1–9 only, and never repeat a digit within a run.
- The helper shows which sets of digits can make each selected run.
- Every puzzle has exactly one solution.
Tips and strategy
- Start with runs that have only one combination, such as 3 in two squares (1+2) or 17 in two (8+9).
- Where an across run and a down run cross, the digit must be in both runs’ combinations.
- Large totals in short runs need big digits; small totals need small ones.
