A good sudoku app has clean puzzles with one solution, input that suits your hands, proper notes, a fair way of handling mistakes, and nothing that interrupts you mid-puzzle. Puzzle quality is similar across the big apps. The differences you feel every day are in the controls and in the business model. Use the checklist below to test any app in the first ten minutes, before you get attached to a streak.
We make Sudoku Royale, so we mark where it meets each point and where it does not. Some people will want features it does not have, and it is better to know that up front.
1. Interruptions: ads, pop-ups and paywalls
Sudoku rewards focus. An interstitial ad after every puzzle, or a banner under the grid, breaks it. Check three things before you download:
- Does the App Store listing show an In-App Purchases line? That often means a remove-ads or premium tier.
- Does the App Privacy section list Data Used to Track You? Ad networks are the usual reason.
- Do recent one-star reviews mention ads or subscriptions?
Sudoku Royale: no ads, no in-app purchases, no subscription. More in sudoku apps without ads.
2. Input that fits how you play
There are two input orders. Cell first: tap a cell, then a digit. Number first: select a digit, then tap all its cells. Each is faster at a different stage of a puzzle, so an app that supports both without a settings switch is a real advantage. Also check the size of the digit targets. Nine keys across a phone screen are small.
Sudoku Royale: both orders at once. Pick digits on the board, where each digit sits over its own 3x3 box, by tapping or by sliding from the cell. Or select a digit on the number row and tap cells. See number first vs cell first.
3. Notes that stay tidy
Past Easy, you need pencil marks. Look for a clear Notes toggle, fast ways to write the same candidate in several cells, and automatic removal of a candidate from its row, column and box when you place that digit. Some apps also fill in every candidate for you. That saves time, but it skips the part of solving where you notice patterns, so decide whether you want it.
Sudoku Royale: Notes toggle, drag to write a note across cells, a two-finger method for several notes in one cell, and automatic clean-up when you place a digit. It has no auto-fill: you write your own candidates.
Try Sudoku Royale
The classic sudoku you know, without the ads, the pop-ups, or the clutter. A fresh Daily Challenge, unlimited practice with no timer, and technique drills. When you want a rush, race 2 to 18 players on one shared grid.
Download Sudoku Royale: Free on iOS4. How mistakes are handled
This is the most overlooked difference between apps. There are three common designs:
| Design | How it feels | Watch out for |
|---|---|---|
| Wrong digits stay until you check | Closest to paper | Long chains of logic built on one early slip |
| Wrong digits shown in red | Forgiving, fast feedback | Leaning on the red instead of the logic |
| Wrong digits rejected | The board is always correct | No eraser or undo, since nothing wrong is ever placed |
Also check whether the app has a mistake limit that ends your game, and whether you can see how many mistakes you made.
Sudoku Royale: wrong digits are rejected with a shake and never land. In Practice mistakes are unlimited and counted on the result screen. In the Daily Challenge each mistake adds 30 seconds, and after three the run is unranked but you can still finish it. There is no undo or erase button. If you like to try a digit and take it back, that will feel different.
5. Highlighting
Good highlighting cuts scanning time. The two that matter most are shading the row, column and box of the selected cell, and lighting up every copy of a digit. A dimmed key for a finished digit also helps.
Sudoku Royale: all three. Row, column and box shading on the selected cell. Hold a filled cell to light every copy of that digit, a behavior you can turn off with the Highlight Same Number setting. Finished digits dim on the number row. There is no conflict highlighting, since wrong digits never reach the board.
6. Help when you are stuck
A hint that fills in a digit gets you moving. A hint that names the technique teaches you something. Check which kind an app gives, and whether hints are limited or sold.
Sudoku Royale: in Practice, a tip appears after about 90 seconds without progress and points you at a technique. Tips need a connection. The Dojo drills train single techniques like hidden singles and naked pairs.
7. Difficulty range
Beginners need truly easy puzzles, and experienced solvers need puzzles that require real technique. Every puzzle should have exactly one solution. Read our difficulty guide for what the labels usually mean.
Sudoku Royale: Easy, Medium, Hard, Expert, Master and Extreme. The top four unlock as you solve puzzles at the level below. Every puzzle has one solution.
8. Works offline
If you solve on planes or underground, open the app in airplane mode before you rely on it.
Sudoku Royale: Practice and the Dojo work offline. The Daily Challenge needs a connection to download the day's puzzle. Details in offline sudoku apps.
9. Comfort: theme, sound, one hand
Dark mode for night solving, separate switches for music and effects, and a portrait layout you can manage with one thumb.
Sudoku Royale: Appearance set to System, Light or Dark. Separate Music and Sound Effects switches. Portrait on iPhone, any orientation on iPad. No dedicated one-handed mode, but the on-board digit picker keeps your thumb on the grid. See one-handed sudoku.
10. A reason to come back
A daily puzzle, streaks and stats turn sudoku into a small daily habit. Some people want more: technique training, a league, or the option to play someone live.
Sudoku Royale: a Daily Challenge with a leaderboard, a profile with streaks and accuracy, skill tracking, and a weekly Belt League with friends. Live matches exist if you ever want them, and you never have to touch them.
The checklist at a glance
| Check | Sudoku Royale |
|---|---|
| No ads or paywall | Yes |
| Cell-first and number-first input | Yes, both at once |
| Notes with automatic clean-up | Yes |
| Auto-fill candidates | No |
| Undo and erase | No (wrong digits are rejected instead) |
| Same-digit highlighting | Yes, with a setting to turn it off |
| Technique-based hints | Yes, in Practice, online |
| Offline play | Practice and Dojo |
| Dark mode | Yes (System, Light, Dark) |
| Daily puzzle | Yes |
If auto-fill notes or an undo button are must-haves for you, other apps will suit you better, and our iPhone sudoku app ranking covers them. If you want a calm, ad-free board with flexible input, start with the iPhone sudoku walkthrough.
Frequently Asked Questions
What should I look for in a sudoku app?
Check for ads and paywalls, input that supports both cell-first and number-first entry, a solid notes feature, a mistake system you like, same-digit highlighting, a real difficulty range, offline play and a dark mode. Test these in your first ten minutes with the app.
Is it better when a sudoku app fills in notes automatically?
It depends on why you play. Auto-fill saves time on hard puzzles, but writing candidates yourself is how you learn to spot pairs and other patterns. Sudoku Royale does not auto-fill notes; it removes a candidate automatically when you place that digit.
Why does Sudoku Royale have no undo button?
Sudoku Royale rejects wrong digits instead of placing them, so the board only ever holds correct answers. There is nothing to undo or erase. Notes can be removed by picking the same note again.
Which sudoku app has no ads and no in-app purchases?
Sudoku Royale is free with no ads, no in-app purchases and no subscription. You can confirm this for any app on its App Store page by checking for an In-App Purchases line and the Data Used to Track You privacy section.