Regex Tester
Test regular expressions with live match highlighting, groups, and replace.
Examples
Match email addresses (g flag)
Input
Pattern: (\w+)@(\w+)\.(\w+)
Output
Highlights ada@example.com, grace@navy.mil — with groups ada / example / com
Replace with capture groups
Input
Replacement: $1 [at] $2
Output
ada@example.com → ada [at] example
Find all numbers
Input
Pattern: \d+ (flag: g)
Output
Matches every run of digits in the text
About this tool
This free online regex tester lets you build and debug regular expressions with instant feedback. Type a pattern, toggle the flags, and paste in some text — every match is highlighted live, with a breakdown of the capture groups and an optional replace preview. Everything runs in your browser with no upload.
How to use
- Type your pattern in the expression field (no surrounding slashes needed).
- Toggle flags like g (all matches) and i (case-insensitive).
- Paste your text into the test string box to see matches highlighted.
- Optionally add a replacement (use
$1,$2) to preview a substitution.
What you get for each match
- Live highlighting of every match directly in your text.
- Capture groups broken out (
$1,$2, and named groups). - A match count so you can confirm a pattern behaves as expected.
- A replace preview before you commit a find-and-replace.
New to regex?
Regular expressions look cryptic at first but come down to a few building blocks. Our beginner's guide to regex walks through them from scratch, the regex cheat sheet is a quick syntax lookup, and common regex patterns gives you ready-made expressions for email, URLs, dates, and more to test here. To apply a pattern across a block of text, try find and replace.
Frequently asked questions
Is this regex tester free?
Yes — it's a completely free online regular expression tester with no sign-up. Test as many patterns as you like.
Is my text sent to a server?
No. Your pattern and test string are evaluated entirely in your browser with no upload, so nothing leaves your device.
Which regex flavor does it use?
JavaScript's built-in RegExp engine, which shares its core syntax with most modern flavors (PCRE, Python, Java) — character classes, quantifiers, groups, lookarounds, and named groups all work.
What do the flags g, i, m, s, u, y mean?
g finds all matches, i is case-insensitive, m makes ^ and $ match line breaks, s lets . match newlines, u enables full Unicode, and y is sticky matching. Toggle them and the results update live.
How does the replace preview work?
Type a replacement in the optional field and the result appears below. Use $1, $2 for numbered capture groups and $<name> for named ones, exactly like String.replace.
Why are only some matches highlighted?
Without the g (global) flag, a regex matches only the first occurrence. Turn on g to highlight every match in the test string.
Do I need to add slashes or escape my pattern?
No. Type the pattern only — the slashes shown around it are just for display. Escape special characters with a backslash as usual, for example \. to match a literal dot.
Learn more
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