Magpies.

Every row and every column has a list of numbers: the lengths of its blocks of filled cells, in order, with at least one empty cell between two blocks. A filled cell means a magpie left something shiny there; an empty cell means nothing. Work out, from the numbers alone, which cells must be filled and which must be empty.

The grid size changes through the week, from eight by eight on Monday to fifteen by fifteen on Sunday. Every picture has exactly one arrangement of filled cells that fits every number.

A cross is your own note that a cell stays empty. When every number is satisfied, the game checks the picture by itself.

Tap or click a cell: once fills it, twice puts a cross, three times clears it. Hold the button or your finger and drag to sweep the same mark over many cells at once. Nothing lights up while you play: finding a mistake is part of the puzzle.

Check first tells you only how many marks are wrong. Press it again and it shows which. Hint outlines the row or column it is looking at, marks what follows and explains why; press it again to fill it in. Hints are counted and shown when you finish. Clear empties the grid; the clock keeps running.

Keyboard: arrows move, Space or Enter cycles the cell, F fill, X cross, Delete or Backspace clears, P pauses. Undo takes back the last move.

The clock runs from your first move to the last cell and pauses when you leave the tab, which also hides the grid. Your progress, time, history and day streak stay in this browser, and in your account when you are signed in, so you can continue on another device.

Monday and Tuesday are easy (eight by eight), Wednesday and Thursday medium (ten by ten), Friday and Saturday hard (twelve by twelve) and Sunday is the challenge: fifteen by fifteen. The week strip under the grid takes you to the other days; the archive goes back a year, and the practice sets have eight pictures of each level with no date attached.

Difficulty is measured, not guessed: every picture is checked to be solvable by line logic alone (no guessing), and the candidates for a date are ranked by how many settling passes that logic needs. Easy days settle fast; Sunday needs the most passes.

A block bigger than half the line always overlaps itself: work out its leftmost and rightmost position and mark what both agree on.

Once a line's numbers add up (with their gaps) to exactly the line's length, every block's position is forced: no other arrangement fits.

A cross you place narrows the room left for a block, sometimes forcing more cells around it; a filled cell you place can rule out arrangements that miss it.