Legendary Sudoku: The Hardest Puzzles We Rate

Legendary Sudoku starts at ER 10.0 on the Sudoku Explainer scale and has no upper stop. Our own engine generates every grid, and the hardest classic puzzle we have produced so far rates ER 11.1. Classic legendary puzzles hold 20 to 31 clues, 25.3 on average, which is more than Master, because clue count and difficulty are different things.

What this level asks

Legendary is where you find the hardest sudoku puzzles on the site, and ordinary tools run out. You test a candidate, follow where it leads, and then test a second candidate inside that line. Expect many hours of thought. Every Sudoku69 puzzle, Legendary included, can be solved by logic alone, so the answer is always reachable even when the route is long.

Techniques you will meet

Forcing nets begin at 8.5 in Sudoku Explainer and grow harder with depth: you take every candidate of one cell, follow its consequences, and keep whatever all the branches agree on. Bowman's Bingo, the guess-and-verify method, starts at 7.5 and is the only last-resort technique in our registry. You assume a candidate, write out every placement it forces, and wipe the trail if it contradicts. Death blossom is a further extreme-tier tool. Nested forcing chains, a guess inside one chain that needs its own chain to test it, are what push a rating past 10.

Tips for this level

• Keep a written log of every assumption and what it forced.
• Mark which branches ended in a contradiction, so you never repeat them.
• Work on paper if the notes grid gets crowded, and reserve the app for confirming placements.
• Rest between sessions. Autosave keeps your place, and fresh eyes spot a missed single.

Next step

Read about the hardest Sudoku puzzles to see how far the scale goes, or warm up on Master first.