Kolk Sudoku — Play It Online, With the Full Solution

Updated 15 October 2026

Kolk is a 22-clue sudoku from the Sudoku Players’ Forum list of the hardest known puzzles, where it is rated SE 11.9 — the same top-of-scale figure as Golden Nugget. It never had the newspaper fame of AI Escargot, which makes it a good test of whether a famous name or the grid itself is what makes a puzzle hard. Play it below, print it, or follow the engine’s solution.

Clues

22

Published SE rating

SE 11.9

Suuudokuuu rater

8.5+, past every implemented technique

Play Kolk in the appPrint Kolk — PDF with the solution

Where Kolk comes from

The forum’s “hardest sudokus” thread is the long-running list where solvers collect and rate the hardest grids they find, and Kolk is one of the named grids on it. Its rating is the forum’s published figure, carried by the Suuudokuuu Infinity corpus, not a Suuudokuuu measurement.

Source: Sudoku Players’ Forum, “The hardest sudokus (new thread)”. Compare it with Silver Plate from the same list, or browse every record grid on the hardest sudoku puzzles page.

The Kolk solution, step by step

Suuudokuuu’s source-available engine solves Kolk in 111 steps, reaching for the cheapest technique that still makes progress, exactly as it does when it rates a puzzle. 21 of those steps are forcing chains: the engine assumes a candidate, follows its consequences until something breaks, and removes the assumption. At 1 points even that runs dry — no technique the engine implements moves the grid — and the walkthrough says so, fills the cell with the fewest candidates from the verified solution, and carries on with logic from there. Every other step is a named deduction you can check by hand.

Along the way the walkthrough uses Full House, Naked Single, Hidden Single, Pointing Pair, Box Line Reduction, Naked Pair, Sashimi X-Wing, AIC and Nishio Forcing Chain.