Hard Printable Sudoku

Free to print, with answers. Hard: as few clues as the puzzle allows, often needing pairs and other advanced techniques.
Building the puzzle…

How to print

Press Print (or Ctrl+P / ⌘P). The puzzle fills page one on A4 or Letter paper and the answer key prints on page two, black on white with no ads. There's a new sudoku puzzle here every day; press New puzzle for as many more as you like.