You may have seen this feature called auto-fill, auto-notes, or just “auto candidates” elsewhere. Ours is called Fill Notes, and it’s a bit of a lightning rod in the Sudoku community, people have real opinions about it. Here’s why we built it, how we use it ourselves, and why it disappears entirely on the two easiest difficulty levels. (Want to see it in action first? Go pick a puzzle and toggle it on.)
Why Fill Notes Exists
If you’ve been solving for a while, marking accurate candidates by hand isn’t difficult, it’s just repetitive: checking every empty cell against its row, column, and box, over and over, cell after cell, puzzle after puzzle. Fill Notes handles that groundwork in one click.
What’s left after that is the actual solving. You’ll still spot your Naked Singles and Hidden Singles, work out your Pointing and Claiming pairs, same as always. Fill Notes just clears the mechanical part out of the way first, so you get to that logic faster, and so you have more time left for the genuinely tricky stuff: the “if this, then that” chains behind moves like an X-Wing or a Skyscraper.
If you’re a purist, you’re welcome to skip the button entirely. Nobody’s watching. You’re not in a tournament, there’s no judge with a clipboard, and no one is docking your score. (Well, you might be docking your own score. That’s between you and you.)
What’s the Debate About, Exactly?
Here’s the friction, honestly stated. A lot of Sudoku culture, especially the competitive side, treats writing candidates by hand as part of the skill, not just a preamble to it. Tournament rules almost always require candidates to be marked manually, no exceptions, and plenty of solvers carry that ethic into their casual play too. To them, an auto-fill button is a bit like a calculator on a math test: technically it gets you to the right answer faster, but it skips the part that was supposedly the point.
The counterargument is just as reasonable. Most people solving a Sudoku on a given morning aren’t training for a tournament. They already know the basic techniques cold, and re-executing them by hand for the hundredth time doesn’t teach them anything new. It’s just friction between them and the puzzle they actually want to solve. Neither side is wrong, exactly. It depends what you’re solving for.
How We Use It Ourselves
Honestly, it depends on the puzzle and the mood. Some days Fill Notes is a jump start, a way to skip the boring part and get to the good stuff. Other days we let candidates build up gradually by hand, one small deduction at a time, because that slower pace is its own kind of satisfying. And sometimes we use it as a check: we work out a cell on our own, then hit Fill Notes just to confirm we weren’t fooling ourselves.
Here’s the part worth remembering: Fill Notes only ever gives you the initial, basic candidate set. It doesn’t do your thinking for you. The real work, narrowing those candidates down through actual logic, is still entirely yours.
One thing to watch for. Say you’ve spent ten minutes narrowing a cell from six candidates down to two, purely through your own reasoning. If you press Fill Notes after that, it will cheerfully undo your progress and reinsert the full basic set. It’s not being rude, it just doesn’t know what you’ve already figured out. If this happens to you, don’t panic! Undo will put you right back where you were.
Why Casual and Tricky Levels Don’t Get Fill Notes
At the Casual (Easy) and Tricky (Medium) levels, Fill Notes tips over from “helpful shortcut” into “basically cheating.” At those difficulties, the candidate list alone is often enough to reveal the one valid answer for a cell. At that point you’re not solving a puzzle anymore, you’re just typing in numbers someone else already found for you. That’s not a Sudoku, that’s a spreadsheet.
So Fill Notes simply isn’t available on those two levels. It would hand you the ending before you’d earned the middle.
It's Still a Game
Everyone solves differently, and that’s exactly how it should be. The only thing that matters is that it stays enjoyable. If a puzzle starts feeling like a chore instead of a game, that’s your cue to step back and change something, the difficulty, the pace, or whether Fill Notes is even the right tool for that particular grid.
Whether you’re chasing a new personal best or just learning to spot your first Jellyfish, don’t lose sight of the fact that this is a game first. Everything else is optional. (Announcing your time to someone who didn’t ask is, regrettably, tradition.)
Ready to try it yourself? Head to the Fun & Games page and give Fill Notes a spin.
