Visualize Regular Expressions with Marbles

If you are one of those people who visualize things physically better than in the abstract, then Regex Marble Run by [bottomless] might be for you. Visualize Regular Expressions with Marbles. You enter a test expression and a string, and the site generates a virtual marble machine that lets you see the regular expression pick apart the string in a physical way.

Click this link, and you’ll see the regular expression “^[hH]ack.[dD][^0-9]*$” which, if you aren’t a regular expression user, might seem a bit cryptic. It is fairly simple if you take it bit-by-bit. The caret character tells it to match the start of the string.

So “^dog” will match “dog” and “dog food” but won’t match “food for a dog.” The following bit “[hH]” will match either “h” or “H”. Then there is “ack” which is just what you think it is. So a string starting with “hack” or “Hack” might match (depending on the rest of the expression.