Regex Checker — Check and Validate Regular Expressions Online

Paste any regex pattern to instantly check if it's valid. Get plain-English error messages for syntax mistakes, then test against your own text with real-time match highlighting.

Why Check Your Regex?

Regex syntax is notoriously easy to get wrong. A misplaced parenthesis, a forgotten escape character, or an ambiguous quantifier can silently break your pattern. This tool validates your regex as you type, catching errors before they reach your code. The error messages are translated from cryptic JavaScript exceptions into clear explanations.

Common Regex Mistakes

The most frequent errors: unmatched groups (opening parenthesis without closing), nothing to repeat (quantifier with no preceding token), invalid escapes (backslash followed by a character that isn't a recognized escape), and unmatched character classes (opening bracket without closing). Each error is shown with a specific fix suggestion.

Real-Time Validation Feedback

Every keystroke triggers validation using JavaScript's native RegExp constructor. Valid patterns show a green checkmark. Invalid patterns show a red indicator with a human-readable error. The tool also highlights syntax elements in different colors — character classes in cyan, groups in green, quantifiers in orange — so you can visually verify your pattern's structure.

Paste your regex pattern below to check it.

/
/g
✅ Valid pattern
No matches

Plain-English Breakdown

(Start of capturing group 1
\wMatch any word character (letter, digit, _)
+One or more times
)End of group
\sMatch any whitespace
(Start of capturing group 2
\wMatch any word character (letter, digit, _)
+One or more times
)End of group