Regex Tester Online — Test Regular Expressions Instantly

Last Updated: April 1, 2026

Last updated: 2026-03-14

I have been writing regex for 12 years and I still test every pattern before using it in production. Not because I do not know regex — because regex is one of those things where being 99% sure means you are wrong 1% of the time, and that 1% will bite you in production at 3 AM.

Why You Need a Regex Tester

Writing regex in your head and hoping it works is like writing SQL without running it. You might be right, but why risk it? A regex tester gives you:

• Instant visual feedback. See matches highlighted in real-time as you type.
• Group extraction. See what each capture group matches, not just the full match.
• Edge case testing. Paste 20 test strings and see which ones match and which do not.
• Explanation. Break down the pattern into human-readable steps.

Common Regex Patterns (Copy-Paste Ready)

Regex Flavor Differences

The same pattern can behave differently in JavaScript, Python, and PCRE. Our tester lets you switch between flavors:

• JavaScript: No lookbehind in older browsers. \d matches only ASCII digits.
• Python:re module. Named groups use (?P<name>...) syntax.
• PCRE: Most feature-rich. Supports recursive patterns, atomic groups, and possessive quantifiers.

Related Tools

According to MDN Web Docs, JavaScript regular expressions follow the ECMAScript specification with some browser-specific extensions.

As Python documentation notes, Python regex supports Unicode matching by default in Python 3.