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The RegExp tester helps you build and test regular expressions. It provides real-time pattern matching, match highlighting, capture group extraction, and text replacement.

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Features

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Pattern testing

Test regex patterns against text:
  • Real-time pattern matching
  • Visual match highlighting
  • Match count and position information
  • Support for all JavaScript regex features
The tester uses native JavaScript RegExp, supporting all modern regex features.

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Match highlighting

See matches highlighted in context:
  • Yellow highlighting for matches
  • Preserve original text formatting
  • Multiple match visualization
  • In-context preview

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Capture groups

Extract and view captured groups:
  • See all capture groups for each match
  • Group numbering (1,1, 2, etc.)
  • Empty group detection
  • Position information for each match

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Text replacement

Replace matched text with patterns:
  • Use capture groups in replacements (1,1, 2)
  • Reference full match with $&
  • Preview replacement results
  • Test replacement patterns

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Flag support

Support for all JavaScript regex flags:
  • g - Global (find all matches)
  • i - Case-insensitive
  • m - Multiline (^ and $ match line boundaries)
  • s - Dot matches all (including newlines)
  • u - Unicode
  • y - Sticky (match from lastIndex)
Enable the global flag (g) to find all matches instead of just the first one.

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Use cases

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Email validation

Validate email addresses: 
Pattern: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}
Test: Contact us at support@example.com or sales@company.org
Matches: support@example.com, sales@company.org

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Phone number extraction

Extract phone numbers in various formats: 
Pattern: \(?\d{3}\)?[-.]?\d{3}[-.]?\d{4}
Test: Call (555) 123-4567 or 555.987.6543 for assistance
Matches: (555) 123-4567, 555.987.6543

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URL matching

Find URLs in text: 
Pattern: https?://[^\s]+
Test: Visit https://example.com or http://test.org for more info
Matches: https://example.com, http://test.org

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Date extraction

Extract dates with capture groups: 
Pattern: (\d{2})/(\d{2})/(\d{4})
Test: Events on 12/25/2024 and 01/01/2025
Matches: 12/25/2024 (groups: 12, 25, 2024)
         01/01/2025 (groups: 01, 01, 2025)

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Hex color codes

Find hexadecimal color values: 
Pattern: #([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})
Test: Colors: #FF5733, #333, #00AAFF, and #F0F
Matches: #FF5733, #333, #00AAFF, #F0F

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Pattern input

The pattern input includes:
  • Delimiters - Visual / delimiters for clarity
  • Pattern field - Enter regex without delimiters
  • Flag checkboxes - Enable/disable flags visually
  • Flag descriptions - Tooltip explaining each flag

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Match display

The matches tab shows:

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Highlighted text

Your test string with matches highlighted in yellow.

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Match details

For each match:
  • Match number badge
  • Position in original text
  • Full matched text
  • Captured groups (if any)
  • Copy button for each match

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Match information

Green badge showing total match count.

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Replace functionality

The replace tab provides:

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Replacement pattern

Enter replacement text using:
  • 1,1, 2, etc. - Captured groups
  • $& - Full match
  • Plain text - Literal replacement

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Replacement result

See the transformed text with all replacements applied.

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Example replacement

Pattern: (\d{2})/(\d{2})/(\d{4})
Replacement: $3-$1-$2
Input: Events on 12/25/2024 and 01/01/2025
Output: Events on 2024-12-25 and 2025-01-01
Use the replace tab to test text transformations before implementing in code.

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Examples

Click “Examples” to load preset patterns:

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Email validation

Pattern: [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} Test string: Contact us at [email protected] or [email protected]

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Phone numbers

Pattern: \(?\d{3}\)?[-.]?\d{3}[-.]?\d{4} Test string: Call (555) 123-4567 or 555.987.6543 for assistance

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URLs

Pattern: https?://[^\s]+ Test string: Visit https://example.com or http://test.org for more info

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Dates (MM/DD/YYYY)

Pattern: (\d{2})/(\d{2})/(\d{4}) Test string: Events on 12/25/2024 and 01/01/2025

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Hex colors

Pattern: #([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3}) Test string: Colors: #FF5733, #333, #00AAFF, and #F0F

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Quick reference

The tester includes a quick reference panel:

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Character classes

  • \d - Digit (0-9)
  • \w - Word character (a-z, A-Z, 0-9, _)
  • \s - Whitespace
  • . - Any character (except newline without s flag)

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Quantifiers

  • * - 0 or more
  • + - 1 or more
  • ? - 0 or 1
  • {n} - Exactly n times
  • {n,} - n or more times
  • {n,m} - Between n and m times

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Anchors

  • ^ - Start of string (or line with m flag)
  • $ - End of string (or line with m flag)
  • \b - Word boundary

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Groups and alternation

  • (x) - Capture group
  • (?:x) - Non-capturing group
  • x|y - x or y (alternation)
  • [abc] - Any of a, b, or c
  • [^abc] - Not a, b, or c

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Keyboard shortcuts

  • Cmd/Ctrl + Enter - Test pattern
  • Cmd/Ctrl + K - Clear all inputs
  • Cmd/Ctrl + C - Copy matches or replacement result

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Tips

Enable the global (g) flag to see all matches instead of just the first one.
Use capture groups to extract specific parts of matches, like area codes from phone numbers.
The case-insensitive (i) flag is useful for matching text regardless of capitalization.
Test your regex with edge cases to ensure it handles all expected input variations.

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Common patterns

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Username

^[a-zA-Z0-9_]{3,16}$
3-16 characters, letters, numbers, underscores only.

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Password strength

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$
At least 8 characters, one uppercase, one lowercase, one digit, one special character.

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IP address

^(?:[0-9]{1,3}\.){3}[0-9]{1,3}$
Basic IPv4 address format.

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Credit card

^(?:4[0-9]{12}(?:[0-9]{3})?|5[1-5][0-9]{14})$
Visa or Mastercard numbers.

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Error messages

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Invalid pattern

Displays the JavaScript regex error message when the pattern is syntactically invalid.

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No matches

Shows a toast notification when the pattern doesn’t match any text.

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Success

Displays the number of matches found when testing succeeds.

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