Regex Tester

Understanding Regular Expressions

Regular expressions (regex) are powerful patterns used to match, search, and manipulate text. They're widely used in programming, text editors, search engines, and data validation. This regex tester helps you build and test regular expressions in real-time.

🔤 Basic Regex Syntax

Here are the most commonly used regex patterns and their meanings:

Pattern	Description	Example
.	Any character (except newline)	a.b matches "acb", "a1b"
\d	Any digit (0-9)	\d\d\d matches "123"
\w	Word character (a-z, A-Z, 0-9, _)	\w+ matches "hello_123"
\s	Whitespace (space, tab, newline)	\s+ matches " "
^	Start of string/line	^Hello matches "Hello world"
$	End of string/line	world$ matches "Hello world"
*	Zero or more	ab*c matches "ac", "abc", "abbc"
+	One or more	ab+c matches "abc", "abbc"
?	Zero or one	ab?c matches "ac", "abc"
{n}	Exactly n times	a{3} matches "aaa"
{n,m}	Between n and m times	a{2,4} matches "aa", "aaa", "aaaa"
[abc]	Character class	[aeiou] matches vowels
[^abc]	Negated character class	[^0-9] matches non-digits
()	Capturing group	(ab)+ captures "ab", "abab"
(?:)	Non-capturing group	(?:ab)+ matches but doesn't capture
\b	Word boundary	\bword\b matches whole word only

🚩 Regex Flags

Flags modify how the regex engine interprets the pattern:

• g (global): Find all matches, not just the first one
• i (case-insensitive): Ignore case when matching
• m (multiline): ^ and $ match start/end of each line
• s (dotAll): . matches newlines too
• u (unicode): Enable full Unicode support
• y (sticky): Match only from lastIndex position

💡 How to Use This Tool

1. Enter your regex pattern in the pattern field
2. Select flags by checking boxes or typing in flags field
3. Enter test text in the test string area
4. View results - matches are highlighted in yellow
5. Review match details - see index, groups, and captured text
6. Try common patterns - click any pattern card to use it

🎯 Common Use Cases

• Email validation: Check if text contains valid email addresses
• Phone number extraction: Find phone numbers in text
• URL matching: Identify and extract URLs
• Text replacement: Find and replace patterns
• Data validation: Validate input formats
• Log parsing: Extract information from log files
• String manipulation: Split, trim, or transform text

⚠️ Common Mistakes

• Forgetting to escape: Special characters need backslash (\., \*, \+, etc.)
• Greedy vs lazy: Use ? after quantifiers for lazy matching (*?, +?, ??)
• Character class confusion: Inside [], most special chars lose meaning
• Anchors in middle: ^ and $ only work at start/end of pattern
• Overusing .*: Be specific instead of matching everything

🔍 Tips for Better Regex

• Start simple: Build patterns incrementally
• Test thoroughly: Use various test cases
• Use comments: Add comments for complex patterns
• Break it down: Use groups to organize complex patterns
• Validate edge cases: Test empty strings, special characters