Regex Tester

What is Regular Expression

A Regular Expression (Regex) is a mini-language for describing string matching patterns. It's used extensively for text search, data validation, and string replacement — virtually every programming language and text editor has a built-in regex engine.

Common Metacharacters

Pattern	Meaning	Pattern	Meaning
.	Any char (except newline)	^	Start of string
\d	Digit [0-9]	$	End of string
\w	[a-zA-Z0-9_]	(abc)	Capture group
\s	Whitespace	a|b	a or b
[abc]	Character class	[^abc]	Negated class

Quantifiers

* 0+ · + 1+ · ? 0 or 1 · {n} exactly n · {n,m} n to m

Flags

g global · i case-insensitive · m multiline (^$ match each line) · s dotAll (. matches newlines)

Common Patterns

Email   /^[\w.+-]+@[\w-]+\.[a-zA-Z]{2,}$/
Phone   /^\+?[1-9]\d{7,14}$/
URL     /^https?:\/\/[\w\-.]+(:\d+)?(\/\S*)?$/

Common Use Cases

• Form validation: Verify emails, phone numbers, passwords, and other user inputs
• Log analysis: Extract timestamps, IP addresses, and error codes from large log files
• Code refactoring: Batch-rename variables, update import paths, or reformat code
• Data extraction: Pull structured data from unstructured text, strip whitespace or special characters

How to Use

1. Enter your regex pattern in the "Regular Expression" input field and select the desired flags (g/i/m/s)
2. Paste or type your test text in the "Test String" area
3. View real-time highlighted matches, including capture group details and match position indices

FAQ

Why does my regex work in code but not here?

This tool uses the JavaScript regex engine. If your pattern was written for Python, Java, or PCRE, some syntax (like (?P<name>...) named groups or \K lookbehind reset) may not be compatible. Use the JS syntax (?<name>...) instead.

What's the difference between greedy and non-greedy matching?

By default, quantifiers (*, +, {n,m}) are greedy — they match as many characters as possible. Adding ? after a quantifier makes it non-greedy (lazy), matching as few characters as possible. For example, against <div>text</div>, <.*> matches the entire string, while <.*?> matches only <div>.

How do I match special characters literally?

Use a backslash \ to escape them. Use \. to match a literal dot, \( for a parenthesis. Inside a character class [], most special characters lose their meaning, but ], \, ^ (at start), and - (in middle) still need escaping.