SuuudokuuuEvil Sudoku Puzzles (Hell Level)
Updated
Hell is Suuudokuuu’s hardest tier — what most competitors call evil or extreme. A Hell board carries just 17 clues out of 81 cells, the minimum number of clues a sudoku can have and still keep a unique solution. Unlike every other tier, Hell is not generated to a technique band: it is drawn from a bundled corpus of real minimum-clue puzzles, verified by two independent solvers and filtered by SE rating before it ships. In practice that means chains and coloring — X-Chain, XY-Chain, simple coloring and AIC, the technique that generalises all three.
Play Hell Sudoku nowWhat makes a puzzle Hell
A chain follows an alternating sequence of strong and weak links, starting from a candidate and working outward until it proves an elimination or a placement no matter which branch turns out to be true. X-Chain works on a single digit; XY-Chain follows a path of bivalue cells instead. Simple coloring assigns two alternating colours to a network of strong links on one digit and clears any candidate that sees both colours, and AIC generalises the whole family, mixing digits and cell types along one continuous chain. Seventeen clues is not an arbitrary number: it is the smallest clue count mathematically proven to still guarantee a unique solution, which is why the corpus behind this tier is fixed and verified rather than generated fresh for every puzzle.
How hard is it, honestly
Our sample of 40 Hell boards measures SE (Sudoku Explainer) 6.7 to 7.8, with the AIC as the most common hardest step and the Nishio Forcing Chain as the hardest step anything in the sample reached. Be careful about what the clue count is doing here, though: the same sample puts Nightmare at SE 4.5 to 7.3 with 25 clues, which reaches nearly as high while starting with more givens. Seventeen clues makes a puzzle rare and hard to construct; what makes these particular boards hard is the rating filter applied to the corpus, not the number of givens. Our clues versus difficulty guide takes that argument apart properly, and the rating guide publishes the per-tier tables.
Where to go next
Not ready for chains yet? Step back to Nightmare Sudoku, which asks for the same reasoning with more of the grid already filled in. Prefer paper? Download the printable Hell sudoku PDF. Browse the technique index, especially X-Chain, XY-Chain, Simple Coloring and AIC, the how to play guide, the 17-clue sudoku guide, every tier on the Sudoku difficulty levels hub, or head home.
Hell Sudoku FAQ
What techniques do I need for Hell level?
Chains and coloring: X-Chain, XY-Chain, Simple Coloring and AIC, layered on top of every fish, wing and subset technique the earlier tiers already require. A minority of boards in our sample also needed a forcing chain.
How many clues does a Hell sudoku have?
17 clues, the proven minimum for a sudoku with a unique solution.
Is Hell harder than Nightmare?
Only slightly, and not because of the clue count. Our sample measures Hell at SE 6.7 to 7.8 and Nightmare at SE 4.5 to 7.3 — Hell has the higher floor, but the two tiers reach almost the same ceiling.
Why does Hell use a fixed puzzle corpus instead of generating puzzles?
17-clue puzzles are rare and expensive to search for on demand, so Suuudokuuu ships a bundled corpus that has already been checked by a Dancing Links exact-cover solver and a bitmask solver, rated, and filtered by that rating before it is packed.