Regex Tester Online

How to Use the Regex Tester

1. Enter your regex pattern in the pattern input field at the top. The pattern is automatically wrapped in forward slashes.
2. Select flags using the checkboxes. The g (global) flag is enabled by default to find all matches. Enable i for case-insensitive matching, m for multiline mode, or s to make the dot match newlines.
3. Type or paste your test string in the "Test String" area. Matches are highlighted in real time as you type.
4. View match results on the right panel with alternating highlight colors for each match. The match count updates live.
5. Inspect capture groups in the expandable table below. Each match shows the full match and all captured groups.
6. Use Replace Mode to test search-and-replace operations. Enter a replacement string (you can use $1, $2 for captured groups) and click "Replace" to see the result.
7. Browse Common Patterns for ready-to-use regex patterns for emails, URLs, IP addresses, and more.

What Are Regular Expressions?

Regular expressions (regex or regexp) are powerful sequences of characters that define search patterns. They are used across virtually every programming language and text editor for tasks like:

• Validation: Check if input matches an expected format (email addresses, phone numbers, dates).
• Search: Find specific patterns in text, such as all URLs in a document or all dates in a log file.
• Extraction: Pull out specific parts of text using capture groups, like extracting the domain from an email address.
• Replacement: Transform text by replacing matched patterns with new strings, including backreferences to captured groups.

A simple regex like \d+ matches one or more digits, while [A-Za-z]+ matches one or more letters. You can combine these building blocks to create patterns that match complex text structures. Regular expressions are supported in JavaScript, Python, PHP, Java, C#, Ruby, Go, and most other programming languages.

Regex Cheat Sheet

Pattern	Description	Example
.	Any character except newline	a.c matches "abc", "a1c"
*	Zero or more of the preceding element	ab*c matches "ac", "abc", "abbc"
+	One or more of the preceding element	ab+c matches "abc", "abbc" but not "ac"
?	Zero or one of the preceding element	colou?r matches "color", "colour"
^	Start of string (or line in multiline mode)	^Hello matches "Hello world"
$	End of string (or line in multiline mode)	world$ matches "Hello world"
[abc]	Character class: matches a, b, or c	[aeiou] matches vowels
[^abc]	Negated class: any char except a, b, c	[^0-9] matches non-digits
{n,m}	Between n and m repetitions	\d{2,4} matches 2 to 4 digits
()	Capture group	(\w+)@(\w+) captures user and domain
|	Alternation (OR)	cat|dog matches "cat" or "dog"
\d	Digit (equivalent to [0-9])	\d{3} matches "123"
\w	Word character (letter, digit, underscore)	\w+ matches "hello_123"
\s	Whitespace (space, tab, newline)	\s+ matches spaces between words
\b	Word boundary	\bcat\b matches "cat" but not "category"
(?=...)	Positive lookahead	\d+(?= dollars) matches "100" in "100 dollars"
(?!...)	Negative lookahead	\d+(?! dollars) matches digits not before " dollars"
(?:...)	Non-capturing group	(?:ab)+ matches "abab" without capturing

Common Regex Patterns

Frequently Asked Questions