Welcome to the fantastic world of nerdy regex fun! Start playing by selecting one of the puzzle challenges below. There are a wide range of difficulties from beginner to expert.

# How to play

Regex Crossword is a game similar to sudoku or the traditional crossword puzzle, where you must guess the correct letters in the horizontal and vertical lines of a grid. In Regex Crossword you are not given a word to guess, but a pattern that tells you which letters are allowed.

Regex pattern

So how does such a regular expression pattern look like? Well, it can be very simple like [AB], which will match the letter A or B. There are also special characters which indicate how many times a letter can appear in the text, e.g. [AB]* which means that A or B can occur *zero or more times*. The syntax can get a little more advanced than this, but you can always find a quick reference by clicking " Help" in the top right menu above.

## Example solution

Let's walk through a test example, just to get the hang of it. Given the following Regex Crossword puzzle, you first need to look at the patterns, and see if there are some of them, that can only have one solution.

If we look at the first "clue" A*, it means that the first row can have *zero or more* A's. No other letters are allowed, so we just write A's all the way. That was easy!

If we then look at the clue in the first column, AB is actually literally an A followed by B. We already have the A, so we add the B in the last position.

Now we only need to fill in the last position, but the last two clues are a bit more tricky. [CA]* means that the*range* of letters C or A can occur *zero or more* times. The | symbol means *or*, so (B|C)* will match the letter B or C *zero or more* times. If we look at the last column, we already have an A in the first position, and the last position can be either C or A. But the clue in the last row only allow a B or C. Thus a C is the only letter we can put in the last position. Success - we have now solved the puzzle!

This has hopefully prepared you for solving the more challenging puzzles. Have fun!