What to Look For
A good Sudoku app has clean visuals, responsive controls, and multiple difficulty levels. Pencil mark support is essential. A hint system helps when you are stuck. Daily challenges keep you coming back. And most importantly: no aggressive ads that interrupt your solving.
SudokuVault
Our own app has thousands of puzzles at four difficulty levels. It has pencil marks, hints, daily challenges, offline play, and stat tracking. The free version has no ads during gameplay. It is available on both iPhone and Android.
Other Good Options
The New York Times has a Sudoku section in their games app. It is well designed and ad-free for subscribers. Nikoli publishes the original Sudoku app with hand-crafted puzzles from the company that popularized the format. Andoku is a solid Android option with multiple puzzle variants.
Avoid Apps With Constant Ads
Many free Sudoku apps show a video ad after every puzzle or pop up banner ads while you solve. This kills the focus that makes Sudoku enjoyable. Look for apps that keep ads out of the solving screen or offer a reasonable one-time purchase to remove them.
Pencil Marks Are Non-Negotiable
Any Sudoku app worth using must support pencil marks. Without them, you cannot solve medium or hard puzzles. The best apps let you toggle candidates with a single tap and automatically remove candidates when you place a number.
Try Before You Buy
Download two or three apps and solve a few puzzles in each. Pay attention to how the controls feel. Can you place numbers quickly? Are the pencil marks easy to read? Does the hint system actually help? Pick the one that feels most natural to you.