**Letter Sudoku**, also known as **Word Sudoku** or **Alphadoku,** is a variation of the classic Sudoku puzzle that uses letters instead of numbers. The rules for Letter Sudoku on a 9×9 grid are as follows:

**1.** The grid is divided into nine 3×3 sub-grids, also known as “boxes” or “regions.”**2.** Each row of the grid must contain the letters A to I, with no repetition of letters within the row.**3.** Each column of the grid must also contain the letters A to I, with no repetition of letters within the column.**4.** Each 3×3 sub-grid must contain the letters A to I, with no repetition of letters within the sub-grid.**5.** The puzzle starts with some letters already filled in, known as “clues” or “givens.” These letters are the starting point for solving the puzzle.**6.** The goal of the puzzle is to fill in the remaining empty cells with letters from A to I, following the rules above, so that each row, column, and 3×3 sub-grid contains all the letters A to I without any repetition.**7.** As with the classic Sudoku, there is only one solution to a valid Letter Sudoku, and it can be achieved through logical deduction without any guessing or trial-and-error.

Letter Sudoku provides a different and interesting challenge for puzzle enthusiasts who enjoy word-based puzzles.