Regular Expression Tester

Test and debug your regular expressions with real-time highlighting and detailed match information.

Regex Pattern

//

Common Patterns:

Test String

Sample Texts:

Match Results

No matches found
Execution time: 0.00ms

Highlighted Match:

Regular Expression Cheatsheet

Character Classes

.Matches any character except line breaks
\wMatches any word character (alphanumeric & underscore)
\dMatches any digit character (0-9)
\sMatches any whitespace character (spaces, tabs, line breaks)
\WMatches any non-word character
\DMatches any non-digit character
\SMatches any non-whitespace character
[abc]Matches any character in the set
[^abc]Matches any character not in the set
[a-z]Matches any character in the range

Anchors

^Matches the beginning of the string
$Matches the end of the string
\bMatches a word boundary
\BMatches a non-word boundary

Quantifiers

*Matches 0 or more times
+Matches 1 or more times
?Matches 0 or 1 time
{n}Matches exactly n times
{n,}Matches at least n times
{n,m}Matches from n to m times

Groups & Alternation

(abc)Capturing group
(?:abc)Non-capturing group
(?<n>abc)Named capturing group (ES2018)
a|bMatches either a or b

Special Characters

\\Escapes a special character
\nMatches a line feed
\tMatches a tab
\rMatches a carriage return
\0Matches a NUL character

Lookarounds

(?=abc)Positive lookahead
(?!abc)Negative lookahead
(?<=abc)Positive lookbehind (not fully supported in all browsers)
(?<!abc)Negative lookbehind (not fully supported in all browsers)

Flags

gGlobal search (find all matches)
iCase-insensitive search
mMulti-line search
sDot (.) matches newlines too
uUnicode support
ySticky search

Common Patterns

\d{3}-\d{2}-\d{4}US Social Security Number
^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$Email address
^(https?:\/\/)?[\w-]+(\.[\w-]+)+([\w.,@?^=%&:/~+#-]*[\w@?^=%&/~+#-])?$URL
^\+?[1-9]\d{1,14}$Phone number (E.164 format)

How to Use Regular Expressions

Regular expressions (regex) are powerful patterns used to match character combinations in strings. They are widely used for text validation, search and replace operations, and data extraction.

Basic Examples

Validating an Email Address

/^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$/

This pattern checks for a valid email format with a username, @ symbol, domain name, and domain extension.

Finding All URLs

/(https?:\/\/)[a-zA-Z0-9-\.]+\.[a-zA-Z]{2,}/g

This pattern locates URLs in text, matching the protocol, domain name, and domain extension.

Tips for Effective Regex Use

  • Start simple and iteratively refine your pattern as needed
  • Use non-capturing groups (?:...) when you don't need to extract that part
  • Be careful with greedy quantifiers (* and +) as they match as much as possible
  • For complex patterns, consider adding comments with the x flag in supported languages
  • Test your regex thoroughly with different inputs, including edge cases

Performance Considerations

Complex regex patterns can lead to performance issues, especially with large input texts or when using certain features like lookaheads and lookbehinds. Using catastrophic backtracking patterns (like nested quantifiers) can cause extremely slow execution or even browser hangs.