A Sudoku's difficulty level is often the first thing readers notice about a puzzle. For questions and answers showing a puzzle it would be nice to have a relatively objective linkable tester.
The first one is not at all "very, very difficult". I only needed basic techniques and a binary branch-point at G7 (either 4 or 9) to solve it.
A further check of the puzzle in question using SudokuWiki.Org's Grader, (click on the orange "Grader" button), returns "diabolical", which agrees with the presumed overestimate of Thonky.
Is there something that does a better job at grading sudokus out there online? It should be:
- no paywall or login
- include some form of sudoku shorthand in the URL
Failing that, if anyone knows of a good command-line utility that does the job? Preferably a util that's already widely distributed, rather than something that needs compiling...