Regex Tester

Test and debug regular expressions with real-time matching and highlighting

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About Regular Expressions

Regular expressions (regex) are powerful patterns used to match, search, and manipulate text. This free regex tester helps you test and debug regular expressions with real-time matching and highlighting, making it an essential tool for developers working with pattern matching, text processing, form validation, and data extraction.

How to Use:

Enter your regular expression pattern in the regex field and your test text in the text area. The tool will highlight all matches in real-time, show match groups, and display detailed information about each match. You can test different flags (global, case-insensitive, multiline, etc.) to see how they affect matching behavior.

Basic Metacharacters:

^
Caret - Matches the start of a string
Example: ^hello matches "hello" at the start
$
Dollar - Matches the end of a string
Example: world$ matches "world" at the end
.
Dot - Matches any single character (except newline)
Example: a.c matches "abc", "a1c", "a-c"
*
Asterisk - Matches zero or more of the preceding element
Example: ab*c matches "ac", "abc", "abbc"
+
Plus - Matches one or more of the preceding element
Example: ab+c matches "abc", "abbc" (not "ac")
?
Question Mark - Matches zero or one of the preceding element
Example: colou?r matches "color" and "colour"

Character Classes & Shorthand:

\d
Digit - Matches any digit (0-9)
Example: \d3 matches "123", "456"
\w
Word Character - Matches letters, digits, and underscore
Example: \w+ matches "hello", "user123"
\s
Whitespace - Matches spaces, tabs, newlines
Example: hello\s+world matches "hello world"
[abc]
Character Class - Matches any character in brackets
Example: [aeiou] matches any vowel
[0-9]
Range - Matches characters in a range
Example: [a-z] matches any lowercase letter
(group)
Capturing Group - Captures matched text for later use
Example: (\d3)-(\d3) captures area code and number separately

Common Examples:

^\d+$
Numbers only
Matches strings containing only digits from start to end
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
Email validation
Basic email address pattern (simplified)
\b\w4\b
4-letter words
Matches complete words that are exactly 4 characters long
(\d4)-(\d2)-(\d2)
Date format (YYYY-MM-DD)
Matches dates and captures year, month, and day in groups

Regex Flags:

g
Global - Find all matches, not just the first one
i
Case Insensitive - Match regardless of case (A = a)
m
Multiline - ^ and $ match line breaks, not just string boundaries
s
Dot All - . matches newline characters as well
u
Unicode - Treat pattern as a sequence of Unicode code points
y
Sticky - Matches only from the index indicated by the lastIndex property

Use Cases:

  • Form Validation: Validate email addresses, phone numbers, URLs, passwords, and other input formats
  • Text Processing: Extract, replace, or transform text patterns in documents
  • Data Parsing: Parse structured data from unstructured text (logs, CSV, etc.)
  • Search & Replace: Find and replace patterns in code editors or text processors
  • Log Analysis: Filter and extract specific information from log files
  • Code Refactoring: Find patterns in codebases for automated refactoring

Tips & Best Practices:

  • Use anchors (^ and $) when you want to match the entire string
  • Escape special characters with a backslash (\. to match a literal dot)
  • Use character classes [0-9] instead of \d if you need specific behavior
  • Test your regex with various inputs, including edge cases and empty strings
  • Use non-capturing groups (?:group) when you don't need to capture the match
  • Be mindful of regex performance with very long strings or complex patterns
  • This tool works entirely in your browser - no data is sent to servers, ensuring privacy