Daily Killer Sudoku
The two extra rules
Normal sudoku, plus the dashed cages. The small number in a cage's corner is the sum of its digits, and a digit cannot repeat inside a cage even if the cage spans two boxes.
Most of these start with no given digits at all. The sums are enough.
Where to start
Look for the extremes. A two cell cage summing to 3 can only be 1 and 2. One summing to 17 can only be 8 and 9. Those pin down a box fast.
Then use the fact that every row, column and box holds 1 to 9 exactly once, so each sums to 45. Add up the cages sitting inside one and whatever is left over is forced.
Controls
Click a cell and type a digit, or use the pad. Space toggles pencil marks. Arrow keys move. Progress saves in this browser as you go.
Why Killer Needs No Given Digits
A normal sudoku has to hand you digits to get started. A killer does not, because the cage sums carry the same information in a denser form. A cage of two cells summing to 17 tells you more than a single given 8 would, since it fixes two cells at once and rules those digits out of everything around them.
Every puzzle here was generated and then proved solvable by a solver that is only allowed techniques a person can use: cage combinations, the rule that each row, column and box sums to 45, singles and naked pairs. If it needed a guess anywhere, it was thrown away rather than published.
More to Play
There is a daily thermo sudoku if you prefer your constraints drawn rather than counted, and 2048 for something faster. All of them are on the games page, and the puzzle tools solve real objects.