regex101
A regular expression tester that explains each token as you type, highlights matches live and shows why a pattern failed. Turns regular expressions from guesswork into something you can debug.
Tool
Other
regex101
Minutes per use
All
Free
What it is
A browser tool for building and testing regular expressions, with live match highlighting, a token by token explanation of your pattern, a reference panel, and support for the differing syntax of several languages.
Why the explanation panel matters
Regular expressions are usually written by copying something close and adjusting it until it works, which means people who use them daily still cannot read them. Watching the tool name each element as you type teaches the syntax as a side effect of getting your work done.
The feature people miss
The debugger, which steps through how the engine attempts a match. It is the only practical way to understand why a pattern is catastrophically slow or why it matched more than you expected.
Best for: anyone who writes regular expressions, which is most developers, occasionally and reluctantly.
Ready to start?
Opens on regex101 in a new tab.
Stuck on something specific?
Writing only gets you so far. If you want an answer to your situation rather than the general case, book a session and we will work through it together. Every session is free; a few slots open each week.
Follow along
New writing, resources and project ideas land here first.