Regex Tester

About the Regex Tester

Regular expressions are powerful and famously fiddly. This tester gives you a tight feedback loop: type a pattern and instantly see what it matches, highlighted right in the text, with every capture group broken out beside it. When the pattern does what you want, copy a ready-to-run snippet for the language you're working in.

It runs entirely in your browser. Your patterns and test text never touch a server — handy when you're testing against real log lines, customer data, or anything you'd rather not paste into a random website.

What you get

• Live highlighting. Every match is highlighted in the test string, with alternating colors so adjacent matches stay readable. Hover a match to link it to its capture breakdown.
• Capture groups, side by side. Each match lists its full text plus every numbered and named group, so you can see exactly what your parentheses capture.
• A ready-made playground. The built-in sample paragraph is packed with the things people actually parse — emails, URLs, phone numbers, prices, dates, IPs, hex colors, hashtags, and versions.
• One-click pattern library. Load battle-tested patterns for email, URL, phone, date, price, IPv4, hex color, hashtag, mention, and more.
• Flags that make sense. Toggle global, ignore-case, multiline, dotall, unicode, and extended (verbose) mode and watch results update.
• Find & replace. Try a replacement using $1, $2, $& and preview the rewritten text.

Code for your language

Pick a language and the tool writes a copy-paste snippet that compiles your pattern with the right flags and iterates the matches — for JavaScript, Python, R, Java, C#/.NET, PHP, Ruby, Go, and grep (PCRE). It handles the awkward bits for you: raw strings in Python, doubled backslashes in Java and R, perl = TRUE in R, inline flags where a language has no flag argument, and the (?P<name>) vs (?<name>) named-group syntax difference between Python and the rest.

Good to know

• Matching uses your browser's JavaScript regex engine. The vast majority of everyday patterns behave identically across languages, but engines differ on advanced features — lookbehind, recursion, possessive quantifiers, and POSIX classes like [[:alpha:]] aren't all portable. The generated snippet notes per-language quirks.
• Go uses the RE2 engine, which intentionally omits backreferences and lookaround; Ruby treats ^/$ as line anchors by default and uses /m for dotall. The notes call these out.
• You can paste Python-style named groups (?P<name>…) — they're understood here and converted appropriately in each snippet.

No account, no watermark, no upload — just iterate until the pattern is right.

Common questions

How do I test a regular expression?

Type the pattern and paste sample text: matches highlight live as you edit, so every tweak gets instant feedback. When it works, copy runnable code for your language, escaping included.

How do I see what my capture groups matched?

The side-by-side breakdown lists every match with each group's captured text labeled, which ends the guessing about which parenthesis grabbed what.

Can I get the regex as code for Python or JavaScript?

Yes: one click exports working snippets for Python, JavaScript, R, Java, and more, with the pattern properly escaped for each language's string rules.

Why does my regex work here but not in my code?

Usually escaping (backslashes doubling in string literals) or flavor differences between engines. The exported code handles the escaping correctly, which eliminates the most common culprit.

Is it safe to test regex against real production data?

Here, yes: the matching runs in your browser, so the log lines and user data you paste never travel. That is the difference between this and testing on a server-side regex site.

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