Regex Tester

Test, replace, and split with regex — live highlighting, capture groups, shareable URLs.

Pattern

//gi

⚠ Nested quantifiers detected (e.g. (a+)+). On long inputs this can cause catastrophic backtracking and freeze the tab. Consider rewriting with atomic alternatives.

Test string

Highlighted2 matches

Contact us at hello@toolsflip.com or support@example.org.
Bad: foo@, @bar.com, plain text.

Matches

#1hello@toolsflip.comat index 14

#2support@example.orgat index 37

Regex cheatsheet

.any character except newline

\ddigit (0-9)

\Dnon-digit

\wword char [A-Za-z0-9_]

\Wnon-word char

\swhitespace

\Snon-whitespace

\bword boundary

^start of line/string

$end of line/string

*0 or more

+1 or more

?0 or 1 (or lazy)

{n}exactly n times

{n,m}n to m times

[abc]any of a, b, c

[^abc]none of a, b, c

a|ba or b

(abc)capture group

(?:abc)non-capturing group

(?<name>abc)named capture group

(?=abc)lookahead

(?!abc)negative lookahead

(?<=abc)lookbehind

Free Online Regex Tester

Build and debug regular expressions in real time with our free online regex tester. Type a pattern, flip the flags you need, and watch every match highlight instantly. Switch to Replace mode to preview String.replace with substitutions like $1 and $&, or Split mode to see how your regex breaks a string apart. Share any regex with a single click — the tool encodes your pattern, flags, and test string into the URL so teammates land on the exact same state. Everything runs in your browser; your patterns and text never leave your device.

How to Use

Pick a mode: Match highlights results, Replace previews substitutions, Split shows the split parts.
Type or paste your regex into the Pattern field. Load a preset to start from a known-good pattern.
Toggle flags — g for all matches, i for case-insensitive, and more.
Paste the text you want to match in the Test string box.
Click Share link to copy a shareable URL, or Copy regex for the full literal.

Flag Reference

g — global, finds every match instead of just the first.
i — case-insensitive matching.
m — multiline, so ^ and $ match at line breaks.
s — dotall, so . matches newlines.
u — unicode, enables full unicode handling and \p{…} escapes.
y — sticky, matches only from lastIndex.

Who Uses a Regex Tester?

Developers validating email, phone, and password inputs. Data and QA engineers cleaning CSVs, logs, and API responses. DevOps folks writing grep, sed, nginx, and alerting rules. Security researchers building detection patterns. Writers running find-and-replace across long documents. Anyone who writes a regex wants to confirm it works before shipping it — this tool is that sandbox.

Why Use Our Regex Tester?

Three modes — match, replace, and split — in one tool.
Live matching with highlighted results as you type.
Nine real-world presets: email, URL, IPv4, phone, hex color, ISO date, UUID, price, HTML tag.
All six JavaScript regex flags with plain-English tooltips.
Capture groups and named groups shown for every match.
Shareable URLs — send a link with your exact pattern + test string.
Built-in cheatsheet, copy-to-clipboard, execution time, and zero-width loop safety.
Runs 100% in your browser — no uploads, no tracking of your patterns.

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