Use the number pad or keyboard to enter values. Turn Notes on, or hold Shift while pressing a number, to add candidate marks. Press Enter to commit the current value while keeping focus on the same cell. Walkthrough mode locks the board for review.
Milestone 10 continues here: choose a puzzle image, detect the puzzle area, review the recognized givens, validate them, then import the corrected puzzle into the board.
The image stays in the browser. Detect the puzzle area to estimate the four corners, drag the handles if the outline catches artifacts, and prepare future coordinate-based OCR. Then enter or paste the recognized givens and use Validate before importing.
The detected puzzle area and normalized coordinate map will appear here.
Fill only the starting clues from the image. Blanks stay empty.
A page-by-page learning guide for solving, taking notes, using Assist, reviewing walkthroughs, exploring What-If branches, and saving progress.
You will learn: The basic flow for starting a puzzle, getting help, and reviewing your solve.
Load an example, generate a random puzzle, or choose Blank Puzzle to enter your own givens. The board is editable until you solve it, ask the app to solve it, or enter walkthrough review mode.
Sudoku Skills records your manual entries as you solve. If you finish the puzzle yourself, your own path becomes a walkthrough you can review step by step.
What to notice: The app is built around learning. Every action either helps you solve or helps you review how the puzzle was solved.
You will learn: How to read R#C# cell names and box numbers used in walkthrough explanations.
A Sudoku grid has 9 rows, 9 columns, and 9 boxes. Each cell can be named by row and column. For example, R4C1 means row 4, column 1.
You do not need to memorize box numbers. The app shows them when needed. Knowing R#C# and box numbers simply makes the walkthrough easier to follow.
What to notice: Box numbers run left to right and top to bottom. R4C1 is the first cell in row 4 and belongs to box 4.
You will learn: How to use the board, number pad, keyboard, and Enter key while keeping your solve recorded cleanly.
Select a cell, then use the number pad or keyboard to enter a value. Use Clear or Backspace/Delete to remove an editable value.
Press Enter to commit the current cell without moving focus. This is useful when you want the walkthrough recording to capture the current value right away.
What to notice: The number pad and keyboard do the same thing. Enter commits the selected cell and keeps focus where it is.
You will learn: How notes help you think without changing the puzzle solution.
Use the Notes pill for Pencil marks, or hold Shift while pressing a number, to add or remove candidate marks in an empty cell. Notes never affect solving, but they are saved with your puzzle.
Try toggling notes in the demo. Candidate notes are for your own thinking; Validate, Hint, and Solve only care about placed values.
What to notice: Notes appear as small marks inside the cell. Tapping the same number again removes that note.
You will learn: How blue hatches show which numbers are eliminated from contention for that cell.
Blue hatches are cell-focused. They are the quickest way to see which numbers are eliminated from contention for that cell. They mark the selected cell's row, column, and box peers. These are the only cells that can affect which numbers can go in the selected cell.
When to use it: Use Blue Assist when you want to understand what values are ruled out for one selected cell.
What to notice: The blue hatches instantly reveal every cell that shares R7C9's row, column, or box. Those are the cells that can rule numbers out for R7C9.
You will learn: How yellow hatches and red circles show where a chosen value can and cannot go.
Yellow hatches are value-focused. Red circles mark matching values already on the board. Yellow hatches show cells where those matching values rule out the same value.
When to use it: Use Yellow Assist when you want to see where a specific value can still fit in a row, column, or box.
What to notice: Red circles show the 9s already placed. Yellow hatches show the cells those 9s block, making the remaining safe location easier to see.
You will learn: How Validate and Hint help without erasing your recorded solve.
When you load a puzzle, Validate only highlights the cells you entered that are wrong. It leaves the original givens alone.
Hint fills one verified solution cell, highlights it, and lets you keep solving manually. Hint values remain purple so you can quickly see which cells were filled by the app.
What to notice: R4C1 should be 1. If 4 is entered there, Validate marks that exact cell red and leaves the givens alone.
What to notice: A correct manual entry is left alone. Validate focuses attention only on cells that need fixing.
What to notice: The first safe hint fills R4C1 with 1. Purple means the app supplied the value while your manual solve continues.
You will learn: How puzzle-area detection and scan review turn an image into trusted givens before solving starts.
Choose a Sudoku image from your device, then detect the puzzle area to create a local four-corner, perspective-corrected preview and coordinate map. If the detector catches a nearby artifact, drag the purple corner handles onto the outside Sudoku border before reviewing the givens. OCR is not connected yet, so you can enter or paste the recognized givens while checking the detected puzzle area.
Detect puzzle area estimates the puzzle corners, corrects skew when possible, lets you adjust the corners manually, and creates the coordinate map that future OCR will use. Validate checks the reviewed givens with the same Sudoku engine used by the main board. Red cells need attention. Once the scan is logically valid, Import to board locks those givens and lets you use Hint, Solve, Save, Recent, and walkthroughs normally.
What to notice: Scan import is conservative. It speeds up entry, but the app asks you to confirm anything uncertain before the puzzle becomes a locked set of givens.
You will learn: How the app turns solving into a step-by-step lesson.
Solve completes the puzzle and opens a teaching walkthrough. Each logical step teaches one placement at a time: one cell, one value, one reason.
Manual solving is recorded too. When you enter the final correct value, the app adds a Solved step and switches to review mode so you can replay your own path.
While reviewing a walkthrough step, turn Assist on to see the row, column, and box context visually.
R4C1 has candidates 1, 4, and 8. But in box 4, only 1 can go in R4C1.
Technique: Hidden Single in a boxWhat to notice: The walkthrough title tells you the placement. The reason explains why that value is now safe.
You will learn: Why a hard puzzle may require a controlled What-If path.
Sometimes no safe logical placement is available. A strong solver does not guess randomly. They choose the box with the fewest valid combinations, try one path, and backtrack if it creates a contradiction.
Sudoku Skills shows that process so you can study why one path succeeds and the others fail.
What to notice: The guess is limited and testable. The app records what happens so you can learn from the branch.
You will learn: How What-If lets you test a branch without losing the real puzzle state.
What-If lets you safely explore "what would happen if I tried this combination?" This is exactly what strong solvers do when they get stuck.
When a What-If path fails, the app highlights the exact cell that caused the contradiction and shows which guessed values will be removed when it rewinds.
What to notice: Both cards show box 3 only. Purple cells are the values being tested in that combination, matching the live What-If cards.
You will learn: How saved puzzles, mobile review, and offline app behavior work.
Save stores the givens, current board, candidate notes, and manual replay steps. Recent saved puzzles can be loaded or removed. Restart returns a loaded puzzle to its givens, or clears a fully manual board.
You can keep the app shell available offline, but puzzle actions that need the server require a connection.
What to notice: Saved puzzles include more than the board. They also preserve notes and your manual replay history.
You will learn: The words used in walkthroughs, hints, validation, and What-If branches.
These terms appear throughout the app. You can come back to this page whenever a walkthrough phrase is unfamiliar.
Common beginner mistake: checking only a row or column and forgetting the box. Every placement must satisfy all three: row, column, and box.