https://pencilmark.pages.dev/2026-09-24 https://pencilmark.pages.dev/explore/2026-09-24 https://pencilmark.pages.dev/learn/2026-09-24 https://pencilmark.pages.dev/learn/classic/2026-09-24 https://pencilmark.pages.dev/learn/marks/2026-09-24 https://pencilmark.pages.dev/learn/killer/2026-09-24https://pencilmark.pages.dev/media/killer.jpgKiller Sudoku Rules Explained in One Short ExampleA three-cell cage with a total of 6 shows how killer sudoku works. 2 + 2 + 2 adds up to 6 but repeats a digit, so the cage must hold 1, 2 and 3.https://pencilmark.pages.dev/media/killer.mp4152026-09-23yes https://pencilmark.pages.dev/learn/xv/2026-09-24https://pencilmark.pages.dev/media/xv.jpgXV Sudoku Rules Explained in One Short ExampleA four-cell row with an X and a V shows the XV rule. 3 and 7 add up to 10 across the X, 2 and 5 fail the V because they make 7, and 1 and 4 make the 5 the V needs.https://pencilmark.pages.dev/media/xv.mp4182026-09-23yes https://pencilmark.pages.dev/learn/kropki/2026-09-24https://pencilmark.pages.dev/media/kropki.jpgKropki Sudoku Dots Explained in One Short ExampleA four-cell row with a white dot and a black dot shows the Kropki rules. 4 and 5 fit the white dot, 3 and 7 fail the black dot, and 3 and 6 pass because 6 is double 3.https://pencilmark.pages.dev/media/kropki.mp4182026-09-23yes https://pencilmark.pages.dev/learn/thermo/2026-09-24https://pencilmark.pages.dev/media/thermo.jpgThermo Sudoku Rules Explained in One Short ExampleA four-cell thermometer shows the rule. 2, 5, 7, 3 fails because 7 drops to 3, and 2, 5, 7, 8 climbs all the way from the bulb to the tip.https://pencilmark.pages.dev/media/thermo.mp4152026-09-23yes https://pencilmark.pages.dev/learn/arrow/2026-09-24https://pencilmark.pages.dev/media/arrow.jpgArrow Sudoku Rules Explained in One Short ExampleA circle holding 9 sits at the start of a three-cell arrow. 1, 3 and 6 add up to 10, which is too big, and 2, 3 and 4 add up to exactly 9.https://pencilmark.pages.dev/media/arrow.mp4182026-09-23yes https://pencilmark.pages.dev/learn/whisper/2026-09-24https://pencilmark.pages.dev/media/whisper.jpgGerman Whispers Sudoku Explained in One Short ExampleA four-cell green line starts with 2 and 7, which are 5 apart. 7 then 4 fails because they are only 3 apart, and 2, 7, 1, 8 swings low, high, low, high.https://pencilmark.pages.dev/media/whisper.mp4182026-09-23yes https://pencilmark.pages.dev/learn/renban/2026-09-24https://pencilmark.pages.dev/media/renban.jpgRenban Lines Explained in One Short ExampleA four-cell purple line shows the renban rule. 5, 3, 7, 4 fails because the set skips 6, and 5, 3, 6, 4 passes because 3 to 6 is an unbroken run in any order.https://pencilmark.pages.dev/media/renban.mp4152026-09-23yes https://pencilmark.pages.dev/learn/palindrome/2026-09-24https://pencilmark.pages.dev/media/palindrome.jpgPalindrome Sudoku Lines Explained in One Short ExampleA gray line runs diagonally across three cells. It starts with 7 and has a 2 in the middle, so the far end must be 7 as well.https://pencilmark.pages.dev/media/palindrome.mp4152026-09-23yes https://pencilmark.pages.dev/learn/dutch/2026-09-24https://pencilmark.pages.dev/media/dutch.jpgDutch Whispers Sudoku Explained in One Short ExampleAn orange line shows the Dutch whispers rule. 1, 5, 3 fails because 5 and 3 are only 2 apart, and 1, 5, 9, 4 works because every step is 4 or more.https://pencilmark.pages.dev/media/dutch.mp4152026-09-23yes https://pencilmark.pages.dev/learn/entropic/2026-09-24https://pencilmark.pages.dev/media/entropic.jpgEntropic Lines Sudoku Explained in One Short ExampleA four-cell line starts 1, 8, 4, which is one low, one high and one middle digit. A 7 in the last cell fails because 8, 4, 7 has two highs, and a 2 works.https://pencilmark.pages.dev/media/entropic.mp4182026-09-23yes https://pencilmark.pages.dev/learn/parity/2026-09-24https://pencilmark.pages.dev/media/parity.jpgParity Lines Sudoku Explained in One Short ExampleA four-cell parity line starts 3, 8, 2, which fails because 8 and 2 are both even. 3, 8, 7, 4 passes because it goes odd, even, odd, even.https://pencilmark.pages.dev/media/parity.mp4152026-09-23yes https://pencilmark.pages.dev/learn/regionsum/2026-09-24https://pencilmark.pages.dev/media/regionsum.jpgRegion Sum Lines Explained in One Short ExampleA five-cell line crosses a box border. The piece in the first box is 1, 2 and 6, which adds up to 9, so the piece in the next box must also make 9 with 4 and 5.https://pencilmark.pages.dev/media/regionsum.mp4152026-09-23yes https://pencilmark.pages.dev/learn/between/2026-09-24https://pencilmark.pages.dev/media/between.jpgBetween Lines Sudoku Explained in One Short ExampleA four-cell between line has circles of 2 and 7. An 8 on the line fails because it is outside 2 to 7, and 5 and 4 both fit.https://pencilmark.pages.dev/media/between.mp4182026-09-23yes https://pencilmark.pages.dev/learn/antiknight/2026-09-24https://pencilmark.pages.dev/media/antiknight.jpgAnti-Knight Sudoku Explained in One Short ExampleA 6 sits in the corner of a 3x3 grid, and the two cells a knight's move away light up. A second 6 in one of them breaks the rule, and a 3 in the same cell is fine.https://pencilmark.pages.dev/media/antiknight.mp4152026-09-23yes https://pencilmark.pages.dev/learn/antiking/2026-09-24https://pencilmark.pages.dev/media/antiking.jpgAnti-King Sudoku Explained in One Short ExampleA small grid with a box border down the middle shows the anti-king rule. Two 7s touching diagonally across the border break it, and a 7 with a 2 in the same cells is fine.https://pencilmark.pages.dev/media/antiking.mp4152026-09-23yes https://pencilmark.pages.dev/learn/nonconsec/2026-09-24https://pencilmark.pages.dev/media/nonconsec.jpgNon-Consecutive Sudoku Explained in One Short ExampleThree cells in a row show the non-consecutive rule. 4 and 5 side by side break it, and 4, 7, 2 passes because no neighbors are one apart.https://pencilmark.pages.dev/media/nonconsec.mp4152026-09-23yes https://pencilmark.pages.dev/learn/diagonal/2026-09-24https://pencilmark.pages.dev/media/diagonal.jpgDiagonal Sudoku (Sudoku X) Explained in One Short ExampleA 4x4 example marks one diagonal. Two 3s on the same diagonal break the rule, and a 3 and a 7 on it are fine.https://pencilmark.pages.dev/media/diagonal.mp4152026-09-23yes https://pencilmark.pages.dev/learn/sandwich/2026-09-24https://pencilmark.pages.dev/media/sandwich.jpgSandwich Sudoku Explained in One Short ExampleA row with a clue of 10 shows the sandwich rule. Two cells sit between the 1 and the 9, and 3 + 7 = 10 matches the clue.https://pencilmark.pages.dev/media/sandwich.mp4152026-09-23yes https://pencilmark.pages.dev/learn/little/2026-09-24https://pencilmark.pages.dev/media/little.jpgLittle Killer Sudoku Explained in One Short ExampleA clue of 12 points along the long diagonal of a 3x3 grid. The digits 1, 5 and 6 add up to 12, and digits may repeat on a diagonal when the rest of the grid allows.https://pencilmark.pages.dev/media/little.mp4122026-09-23yes https://pencilmark.pages.dev/learn/oddeven/2026-09-24https://pencilmark.pages.dev/media/oddeven.jpgOdd Even Sudoku Explained in One Short ExampleA four-cell row has a circle and a square. A 5 in the square breaks the rule because 5 is odd, and a 3 in the circle with a 4 in the square passes.https://pencilmark.pages.dev/media/oddeven.mp4152026-09-23yes https://pencilmark.pages.dev/learn/quad/2026-09-24https://pencilmark.pages.dev/media/quad.jpgQuadruple Sudoku Explained in One Short ExampleA circle showing 1 and 3 sits where four cells meet. The 1 and the 3 both appear in those cells, and the other two cells are free.https://pencilmark.pages.dev/media/quad.mp4122026-09-23yes https://pencilmark.pages.dev/learn/extra/2026-09-24https://pencilmark.pages.dev/media/extra.jpgExtra Regions Sudoku Explained in One Short ExampleA shaded diagonal of three cells works like an extra box. Two 5s in the region break the rule, and 5, 1 and 8 pass because they are all different.https://pencilmark.pages.dev/media/extra.mp4152026-09-23yes https://pencilmark.pages.dev/learn/xsums/2026-09-24https://pencilmark.pages.dev/media/xsums.jpgX-Sums Sudoku Explained in One Short ExampleA row with a clue of 10 shows the X-sums rule. The first digit is 3, so you add the first three cells, and 3 + 2 + 5 = 10 matches the clue.https://pencilmark.pages.dev/media/xsums.mp4152026-09-23yes https://pencilmark.pages.dev/learn/fog/2026-09-24https://pencilmark.pages.dev/media/fog.jpgFog of War Sudoku Explained in One Short ExampleA 3x3 grid starts with every cell hidden except the center. Placing a correct 4 there clears the fog and shows the clues underneath, a white dot and a green whispers line.https://pencilmark.pages.dev/media/fog.mp4152026-09-23yes https://pencilmark.pages.dev/learn/glossary/2026-09-24