Sudoku

Fill the grid so that every row, every column and every 3 × 3 box holds the digits 1 to 9 once each — the puzzle everybody knows, played here without the clock most sites put beside it. Pick a cell, pick a digit, keep pencil marks if you like; the only thing the board points out is a digit that already stands in its row, column or box. No hints and no checking as you go: a full grid that is not right yet is told how many cells are off, never which.

A new board every day — Gentle, Steady, and Tricky — the same for everybody, each with a single solution that reasoning alone reaches. No timer and no account needed: a board left half-done waits for you until the day turns, at midnight UTC.