How to Test Regular Expressions Online (Free Regex Tester)

What Is a Regular Expression?

A regular expression (regex) is a pattern that describes text. You use it to find, match, validate, or replace strings — an email address, a phone number, a date, a URL.

Regex is powerful but unforgiving. A single misplaced character changes the match entirely, which is why testing patterns before using them matters.

Why Test Regex Before Using It

A regex that looks right can fail in subtle ways:

• It matches too much (greedy matching)
• It matches too little (missing edge cases)
• It breaks on special characters, spaces, or unicode
• It works on your sample but not on real data

Testing against several inputs catches these problems in seconds.

How to Test a Regex Online

1. Open the free Regex Tester.
2. Paste your regular expression.
3. Paste sample text to test against.
4. See the matches highlighted instantly, and tweak the pattern until it behaves.

Common Regex Building Blocks

Pattern	Matches
\d	Any digit (0–9)
\w	A word character (letter, digit, underscore)
\s	Any whitespace
.	Any character
+	One or more of the previous
*	Zero or more
?	Zero or one (also makes matching lazy)
^	Start of the string
$	End of the string

A Practical Example

To match a simple email:

^[\w.+-]+@[\w-]+\.[\w.-]+$

Break it down: word characters, dots, plus and hyphen before the @, then a domain, a literal dot, and a top-level domain. Test it against several addresses before trusting it.

Regex in Different Languages

The core syntax is shared across JavaScript, Python, PHP, and Java, but flavors differ slightly. Always test in the flavor you will actually use.

After You Test

• Format and validate JSON payloads with the JSON Formatter
• Preview rendered HTML when testing web output with the HTML Preview

FAQ

Is the regex tester free? Yes. The Regex Tester is free and needs no signup.

Which regex flavor does it use? It follows JavaScript regular expression syntax, the same engine used in browsers and Node.js.

Can it replace text too? A tester focuses on matching and highlighting. Use it to confirm your pattern, then apply the replace in your own code.

Why does my regex match too much? Greedy quantifiers like + and * grab as much as possible. Add ? to make them lazy, or anchor the pattern with ^ and $.

Test and fix your patterns instantly with the free Regex Tester.