Regex Tester & Debugger
100% Client-SideTest, edit, and analyze regular expressions in real-time. Safe, local browser-based execution with protection against infinite loops.
Frequently Asked Questions
What is RegEx and why is it useful?
A Regular Expression (RegEx or RegExp) is a sequence of characters that forms a search pattern. It is widely used by developers to perform advanced text search, find-and-replace, and form input parameter validations efficiently.
What does the global flag (g) do?
The global flag (g) specifies that the search should find all matches in the input string, rather than stopping after the first match. If you disable the global flag, only the first match index will be highlighted and itemized.
Why does the tester restrict inputs to 50KB?
To prevent execution lag on lower-end devices or slow viewports, we cap live testing strings at 50KB. Complex regex searches over extremely large datasets can degrade client performance.
Understanding Regex Syntax
Regular expressions use a specialized syntax to locate strings. Here is a summary of standard anchors and sets:
^matches the start of the line or string.$matches the end of the line or string..matches any single character except newline.[abc]matches any character within the brackets (a, b, or c).[^abc]matches any character NOT within the brackets.[a-z]matches any lowercase letter from a to z.
Quantifiers and Groups
Quantifiers indicate the number of times a preceding token must occur:
*matches 0 or more occurrences of the token.+matches 1 or more occurrences of the token.?matches 0 or 1 occurrence (makes it optional).{n}matches exactly n occurrences of the token.{n,m}matches between n and m occurrences.(abc)defines a capture group to remember matches for backreferences.