Regex Tester

Test, debug and analyze complex regular expressions with our powerful tool. Validate patterns, visualize matches, and optimize performance.

Enter your regex pattern. Example: \b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b
Enter text to test against the regex pattern
Test Results
Total Matches
0
Groups per Match
0
Execution Time
0ms
Pattern Complexity
-
Test results will appear here
Matches Details
# Full Match Position Groups
No matches found
Regex Visualization
Regex visualization will appear here
Performance Analysis
Backtrack Steps
-
Number of steps taken during matching
Match Attempts
-
Number of positions attempted
Pattern Length
-
Characters in regex pattern
Complexity Score
-
Estimated regex complexity (1-100)

Performance Tip: Avoid nested quantifiers and complex alternations to improve regex performance.

Replace Function
Use $1, $2, etc. to reference capture groups
Replace results will appear here

Regex Tester & Debugger

Our Regex Tester provides developers with an interactive playground for creating, testing, and debugging regular expressions. This powerful tool offers real-time pattern matching, detailed match explanations, and support for various regex flavors. Whether you're validating user input, parsing text data, or learning regular expressions, this tester helps you write accurate patterns with instant feedback and comprehensive debugging capabilities.

Common Regex Patterns

Email Address
Matches standard email addresses
\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b
URL
Matches HTTP/HTTPS URLs
https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)
Phone Number
Matches US phone numbers
(\+\d{1,2}\s)?\(?\d{3}\)?[\s.-]\d{3}[\s.-]\d{4}
Date (YYYY-MM-DD)
Matches dates in YYYY-MM-DD format
\d{4}-\d{2}-\d{2}
IP Address
Matches IPv4 addresses
\b(?:\d{1,3}\.){3}\d{1,3}\b
HTML Tags
Matches HTML tags
<\/?[a-z][a-z0-9]*[^<>]*>
Credit Card
Matches Visa, MasterCard, Amex
\b(?:4[0-9]{12}(?:[0-9]{3})?|5[1-5][0-9]{14}|3[47][0-9]{13})\b
Hex Color
Matches hex color codes
#([a-f0-9]{6}|[a-f0-9]{3})\b

Regex Cheatsheet

Character Classes
. Any character except newline
\d Digit (0-9)
\D Not a digit (0-9)
\w Word character (a-z, A-Z, 0-9, _)
\W Not a word character
\s Whitespace (space, tab, newline)
\S Not whitespace
Quantifiers
* 0 or more
+ 1 or more
? 0 or 1
{3} Exactly 3
{3,} 3 or more
{3,5} 3, 4 or 5
Groups & Lookarounds
(abc) Capture group
(?:abc) Non-capturing group
(?=abc) Positive lookahead
(?!abc) Negative lookahead
(?<=abc) Positive lookbehind
(? Negative lookbehind
Anchors
^ Start of string
$ End of string
\b Word boundary
\B Not word boundary

Regex Best Practices

Be Specific

Use specific patterns instead of broad ones to avoid false positives.

// Instead of: /.*@.*\..*/ // Use: /\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b/i
Use Non-Capturing Groups

When you don't need to capture group content, use (?:...) for better performance.

// Instead of: /(http|https):\/\// // Use: /(?:http|https):\/\//
Avoid Greedy Quantifiers

Use lazy quantifiers (*?, +?) when possible to avoid matching too much.

// Instead of: /<.*>/ // Use: /<.*?>/
Comment Complex Patterns

Use (?#comment) or x flag with whitespace for complex patterns.

/^(\d{3})-(?# area code)\d{3}-\d{4}$/
Test Edge Cases

Always test your regex with edge cases to ensure it behaves as expected.

// For email regex, test with: // [email protected] // [email protected] // @missinglocal.com // test@domain

Regex Flags Explained

  • i Ignore Case - Case-insensitive matching
  • g Global - Find all matches
  • m Multiline - ^ and $ match start/end of lines
  • s Dot All - . matches newline characters
  • u Unicode - Treat pattern as Unicode
  • y Sticky - Matches only from lastIndex position

Regex Performance Tips

  • Avoid backtracking with greedy quantifiers
  • Use non-capturing groups (?:) when possible
  • Be specific with character classes
  • Anchor patterns when appropriate
  • Test with large inputs to find bottlenecks

Regex Debugging Tips

  • Start with simple patterns and build complexity
  • Test each component separately
  • Use online regex testers to visualize
  • Check for greedy vs lazy quantifiers
  • Verify character classes and boundaries