How to debug and test your regular expression (regex)

Regular expressions are such an incredibly convenient tool, available across so many languages that most developers will learn them sooner or later.

But regular expressions can become quite complex. The syntax is terse, subtle, and subject to combinatorial explosion.

The best way to improve your skills is to write a regular expression, test it on some real data, debug the expression, improve it and repeat this process again and again.

This is why regex101 ( is such a great tool.

Not only does it let you test out your regexes on a sample set, color coding your match groups:

But it also gives you a full explanation of what’s going on under the hood.

You can review the match information:

And even choose your favorite flavor (PHP, JavaScript, Python or Golan)