Best Sudoku App With Notes: Pencil Marks, Auto-Fill, Auto-Clear

If you want the app to fill in pencil marks for you, Brainium Sudoku and Sudoku by Mind The Frog are the ones whose listings say so: Brainium has an Auto-Fill Notes option and Mind The Frog lists "automatic and manual notes". If you prefer writing your own notes and only want the app to tidy them, most good apps do that now: Sudoku.com, Sudoku Now!, Tripledot, Stress Free Sudoku and Sudoku Royale all clear or update notes when you place a number. Sudoku Royale has manual notes with automatic clearing, but no auto-candidates. Which of those you want depends on whether notes are a chore to you or the part of the puzzle where the thinking happens.

The App Store facts

From each app's US App Store listing, checked October 26, 2026. Prices and paid items change, so check the listing before you buy.

Note features compared

Three features matter. Manual notes: you type candidates into a cell. Auto-clear: placing a 7 removes the 7 from notes in the same row, column and box. Auto-fill: the app writes every possible candidate into every empty cell for you. Each competitor cell below quotes or paraphrases its own listing.

Auto-fill: when it helps and when it gets in the way

On a hard puzzle, writing every candidate by hand is slow and easy to get wrong. One missed candidate and an elimination you make later is wrong too. Auto-fill removes that risk and gets you straight to the interesting part: looking for naked pairs, hidden pairs or an X-Wing in a full grid of notes. That is why experienced solvers on Expert-level puzzles often like it.

The cost is on the easier levels and while learning. Filling notes by hand is how you train your eye to see singles. If the app writes them, you can solve a medium puzzle without ever noticing that a cell had only one option, because the app showed it to you. Beginners who start with auto-fill often stall later, when a puzzle needs them to see something the notes alone do not show.

A middle path that many players settle on: write notes by hand, but let the app clear them when you place a number. That keeps the thinking and removes the bookkeeping.

How notes work in Sudoku Royale

Sudoku Royale sits on that middle path, without the option to go further. You turn on the Notes switch under the board and tap candidates into cells; when you place a number, it is removed from the notes in its row, column and box automatically. There is no button to fill in all candidates. If that is the feature you are after, Brainium or Mind The Frog is the better app.

That fits an app built around learning techniques. When you are stuck in Practice, the hint names the technique and points to the cell, then links to a lesson, so you find the elimination in your own notes. The Dojo drills train exactly the patterns that notes reveal, from hidden singles to pointing pairs and X-Wing.

Two input details help with manual notes. You can arm a number on the bar and tap it into several cells in a row, which in Notes mode writes it as a candidate in each. And because every placed number is checked immediately, a wrong digit never sits on the board and spoils the notes around it. There is no undo, so a stray note has to be tapped again to remove it.

Getting more out of notes

• Note late on easy puzzles. Scan for singles first; write candidates only when scanning stops working.
• Look for pairs as soon as cells show two candidates. Two cells in a unit with the same two candidates clear those numbers from the rest of the unit. Our guide to getting unstuck with pairs walks through it.
• Check notes when a puzzle stalls. A missing candidate is the most common reason a hard puzzle seems to have no next move.

Where another app is the better pick

• You want all candidates filled in for you. Brainium Sudoku or Sudoku by Mind The Frog.
• You want to see which notes clash. Stress Free Sudoku highlights pencil marks that have a visible conflict.
• You want undo for notes. Sudoku Now!, Tripledot and Mind The Frog list undo; Sudoku Royale has none.
• You want to turn auto-clear off. Stress Free Sudoku lets you; in Sudoku Royale it is always on.

Our pick

For hard puzzles where you want the grid of candidates handed to you, Brainium Sudoku. For building the skill of reading notes yourself, with the tidying done for you and no ads, try Sudoku Royale. The best apps for learning techniques go deeper on the teaching side, and the comparisons page has every other matchup.