Free Regular Expression (Regex) Tester
Test and debug regular expressions with real-time pattern matching. Perfect for developers working with text processing, validation, and data extraction.
Regex Pattern Tester
Test Results:
Common Regex Patterns
📧 Email Validation
\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b
Matches valid email addresses
📞 Phone Numbers
\(?\d{3}\)?[-. ]?\d{3}[-. ]?\d{4}
US phone number formats
🌐 URL Validation
https?://...
HTTP and HTTPS URLs
🔒 Strong Password
^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])...
8+ chars, upper, lower, digit, special
Understanding Regular Expressions
Regular expressions (regex) are powerful patterns used for matching character combinations in strings. They're essential for text processing, validation, search and replace operations, and data extraction.
Basic Regex Syntax
. (Dot)
Matches any single character except newline
a.c matches "abc", "axc", "a5c"
* (Asterisk)
Matches 0 or more of the preceding character
ab*c matches "ac", "abc", "abbc"
+ (Plus)
Matches 1 or more of the preceding character
ab+c matches "abc", "abbc" but not "ac"
? (Question)
Matches 0 or 1 of the preceding character
colou?r matches "color", "colour"
^ (Caret)
Matches the start of a line
^Hello matches "Hello world"
$ (Dollar)
Matches the end of a line
world$ matches "Hello world"
Character Classes
\d - Digits
Matches any digit 0-9. Same as [0-9]
\w - Word Characters
Matches letters, digits, underscore. Same as [A-Za-z0-9_]
\s - Whitespace
Matches spaces, tabs, newlines
[abc] - Character Set
Matches any character in the brackets
Quantifiers
| Quantifier | Meaning | Example |
|---|---|---|
| {n} | Exactly n times | \d{3} matches "123" |
| {n,} | n or more times | \d{3,} matches "123", "1234" |
| {n,m} | Between n and m times | \d{3,5} matches "123" to "12345" |
Common Use Cases
- **Form validation** - Email, phone numbers, passwords
- **Data extraction** - Parsing log files and structured text
- **Search and replace** - Text processing and cleanup
- **URL routing** - Web framework route matching
- **Input sanitization** - Security and data cleaning
- **Text parsing** - Configuration files and data formats
Regex Flags Explained
Global (g)
Find all matches in the string, not just the first one
Ignore Case (i)
Make the pattern case-insensitive
Multiline (m)
Make ^ and $ match the start/end of each line, not just the string
Frequently Asked Questions
What programming languages support regex?
Almost all modern programming languages support regex, including JavaScript, Python, Java, C#, PHP, Ruby, Go, and more. The syntax may vary slightly between languages.
How do I escape special characters in regex?
Use a backslash (\) before special characters like . * + ? ^ $ { } [ ] ( ) | \. For example, \. matches a literal dot instead of "any character".
What are capture groups?
Capture groups are parts of a regex pattern enclosed in parentheses () that "capture" the matched text for later use. They're useful for extracting specific parts of a match.
Can regex be used for parsing HTML or XML?
While possible for simple cases, regex is not recommended for parsing HTML/XML due to their complex nested structure. Use proper parsers like DOM or SAX parsers instead.