Medium sudoku — the level where Sudoku begins to reveal its real depth — is where many players discover their favourite difficulty to play online. These puzzles suit solvers who are comfortable with basic scanning and want a genuine challenge without venturing into advanced territory. Elimination and scanning will carry you a good distance into the grid, but at some point the straightforward cells will run out and you will need a more deliberate approach. The most important technique to learn for medium difficulty sudoku is naked pairs: when two cells in the same row, column, or 3×3 box share exactly the same two candidate digits — and only those two — you can safely remove those candidates from every other cell in that group. Finding a naked pair often unlocks a chain of simple deductions that fills several cells at once. Before applying this technique, get into the habit of writing all possible candidates in small pencil marks inside each empty cell. Without a clear record of which digits are still available in each cell, naked pairs are almost impossible to spot. Update your candidate list every time you fill in a new digit: cross out that digit from all cells in the same row, column, and box. Medium sudoku online typically takes 20 to 40 minutes and rewards methodical, unhurried thinking above all else. If you are stepping up from Easy, this is the level that teaches you how Sudoku really works.