Every row and every column is an equation, like 7 + 5 = 12, and the equations cross on their numbers. Some cells are already filled; the bank below holds exactly the numbers that are missing. Put each one in its place so that every equation is true. Every grid has a single solution, checked before you see it, and you never have to guess.

• 4levels, from 7×7 to 13×13
• 4daily challenges, the same for everyone
• 2,924daily grids, two years of them, already in the app

Five cells to an equation

A number, an operator, a number, an equals sign and a result. Where a row and a column cross, they share a number, so every number you place has to work both ways.

Four levels

Easy: numbers up to 20, addition and subtraction, on a 7×7 grid. Medium: up to 50, on 9×9. Hard: up to 100, with multiplication and division, on 11×11. Expert: up to 150, on grids up to 13×13.

Logic alone

Four techniques are enough for every grid: working out an equation with one cell left, the only number that fits a cell, the only cell that fits a number, and reasoning across two equations that cross. A grid’s level is the hardest technique it needs.

Four daily challenges, the same for everyone

One grid per level, every day. They were made ahead of time and ship inside the app, so no server is involved: your device reads the day’s grids from its own date. A streak for each level, a calendar of past days, and a share that shows the shape of your grid without the numbers.

A hint in three steps

Where to look, then why, then the answer, which you place yourself. If a number you placed is wrong, the hint says that first. Check turns the wrong numbers red for a few seconds, or shows a green tick.

Played your way

Drag a number to its cell, or tap a cell and then a number. Undo, redo, a timer you can hide, mistakes flagged only if you want them to be. On iPad, the grid and the bank sit side by side. VoiceOver reads each cell with its equations.

Free, and what Pro adds

Free: the four daily challenges, the last seven days of the archive, unlimited practice in Easy and Medium, and your streaks. Pro adds the full archive, practice in Hard and Expert, detailed statistics and four colour themes, paid once and shared with your family. No ads, no account, no lives.

It asks for no permissions at all

Your games and settings stay on the device and, if you leave iCloud on, in your own private iCloud, which we cannot open. Export them as a JSON file from the settings. There is no server of ours and no analytics. The privacy page says the rest.

Thirteen languages: English, French, German, Spanish (Spain and Latin America), Italian, Japanese, Korean, Portuguese (Brazil and Portugal), Russian, Arabic and Chinese (Simplified). iPhone and iPad.

Incastro is being tested and has not been submitted to the App Store. There is nothing to download yet — this page will carry the link when there is.