The Hardest Sudoku Puzzles in the World

Updated 15 October 2026

The hardest sudoku puzzles in the world are not the ones with the fewest clues. They are a small set of hand-crafted or computer-searched grids built specifically to defeat every named human solving technique, leaving only long forcing chains and speculative trial branches to close them out. Clue count decides how much a puzzle gives you up front; it says almost nothing about how far you have to reason once the easy placements run out, and every puzzle on this page proves it.

Researchers rate that reasoning depth with SE (Sudoku Explainer), a community-standard 1.0–12.0 scale that scores a puzzle by the hardest technique its optimal solve path requires — our sudoku difficulty rating guide explains how the technique ladder becomes a number. Suuudokuuu does rate every puzzle it generates, but our source-available rater prices the ladder only as far as forcing chains and reports 8.5 with a ceiling flag above that — so it returns that same figure for every puzzle below. The values quoted here are attributed to their publishers and to the sudoku-solving community that maintains SE-based difficulty trackers, not to our own rater — no single figure below is a Suuudokuuu measurement, and different SE implementations are known to disagree by several tenths at this end of the scale, which is why we attribute rather than link to one disputed number.

The most difficult sudoku puzzles ever published

Every grid below is printed as its source publishes it, and each has exactly one solution. The SE ratings are the figures the source or the solving community attributes to each puzzle; where no source publishes one, we quote none.

AI Escargot (2006)

Finnish mathematician Arto Inkala published AI Escargot in late 2006 and called it the world’s hardest sudoku. The 23 givens trace a spiral across the grid, which is where the name comes from — “escargot” is French for snail. Rated at roughly SE 10.6, it needs chains and forcing logic well beyond the fish and wing patterns that finish most “expert” puzzles, and it remains the puzzle most people mean when they first ask about the hardest sudoku ever made. Source: SudokuWiki, “AI Escargot”.

Play AI Escargot online, print it and read its step-by-step solution.

Easter Monster

Easter Monster comes from the solving community’s lists of the hardest known puzzles, and it is famous less for a number than for a result: Bob Hanson and Dave Marans published a complete logical solution for it in 2008, and SudokuOne calls it perhaps the most difficult sudoku solved without a computer solver. Its givens form an almost symmetrical pattern, and that symmetry is what lets a human-sized proof exist at all. Sources: Hanson and Marans, “Easter Monster” and SudokuOne, “A General Sudoku Logic”.

Play Easter Monster online, print it and read its step-by-step solution.

Golden Nugget

Golden Nugget is a hand-crafted extreme puzzle posted to the Sudoku Players’ Forum as an open challenge, built for maximum resistance to logical solving. It is commonly cited at SE 11.9, level with Everest at the top of the scale, though — as with every puzzle at this end — the exact figure moves depending on which rater produced it. Source: Sudoku Players’ Forum, “Golden Nugget challenge”.

Play Golden Nugget online, print it and read its step-by-step solution.

Platinum Blonde

Platinum Blonde is a computer-generated puzzle built specifically to push the SE scale, commonly cited at roughly SE 10.9. Its 21 givens run in a band from the top-right corner to the bottom-left, so the opening looks deceptively open — the difficulty only shows up once ordinary subset and fish techniques run out and the solve has to fall back on chains and coloring nets that span the whole board at once. Source: sci.math, “Platinum Blonde”.

Play Platinum Blonde online, print it and read its step-by-step solution.

Inkala’s Everest (2012)

Arto Inkala followed AI Escargot with a second puzzle in 2012, again promoted as the world’s hardest sudoku. The solving community nicknamed it “Everest,” and independent raters place it at roughly SE 11.9 — noticeably higher than AI Escargot, and high enough that different SE implementations disagree by several tenths depending on which chain types they model. Source: SudokuWiki, “Arto Inkala Sudoku”.

Play Everest online, print it and read its step-by-step solution.

More record puzzles: Kolk and Silver Plate

Two more named grids from the Sudoku Players’ Forum list of the hardest known puzzles have their own pages, each playable, printable and solved step by step by the same engine as the five above: Kolk, rated SE 11.9 on that list, and Silver Plate, rated SE 11.5.

Why the hardest sudoku in the world defeats human solvers

Every pattern technique on Suuudokuuu’s technique index, up through AIC and X-Chain, justifies one placement or one elimination by reasoning about a fixed, bounded pattern of candidates. The puzzles above are built so that no such bounded pattern ever fires. Solving them means building a forcing chain or a forcing net — following the consequences of a single assumption, sometimes for dozens of steps, until the only way forward is a contradiction that rules the assumption out. The index covers the short forcing chains, starting with the Nishio forcing chain; these puzzles need far longer ones. That is qualitatively different work from spotting an X-Wing: it is closer to a proof by exhaustive case analysis than to pattern recognition, which is exactly why the SE scale keeps climbing past 10.0 for puzzles that a fish-and-wing solver simply cannot touch.

Play these puzzles on Suuudokuuu

Suuudokuuu serves the record puzzles themselves in its Infinity tier: Everest, Platinum Blonde, AI Escargot, Golden Nugget and the rest of a curated set of 100 grids, each checked for a single solution and reshuffled every game so a familiar puzzle never looks the same twice. Prefer paper? The printable Infinity sudoku PDF prints them as originally published.

For the same family of reasoning in shorter doses, play Hell tier, drawn from a bundled corpus that is verified for uniqueness and then filtered to boards that need a forcing chain, or print the Hell sudoku PDF. Hell is hard because of the technique it requires rather than the clue count; seventeen clues is a different fact about a puzzle than “hardest,” and the two get confused constantly — see the 17-clue sudoku guide for why minimal and hard are not the same property. Measured on our own scale, Hell sits clearly past the generated Nightmare tier and still well below the puzzles on this page.