Regex Tester

Regex Tester is a fast, browser-based tool for writing, testing and debugging regular expressions. You type a pattern, paste some sample text, and every match is highlighted instantly — along with the capture groups each match produced.

Regular expressions are compact patterns for describing text: a phone number, an email address, a date, a log line, or anything with a repeating structure. They are powerful but easy to get subtly wrong, and a single misplaced quantifier can silently match too much or nothing at all. A tester lets you see exactly what your pattern does against real input before you paste it into your code.

This tool uses the same regular-expression engine your JavaScript runs on, so what you see here is what you get in the browser, in Node.js, and in most front-end code. It runs entirely on your machine — your patterns and test text never leave the page.

Editing a regex directly in your code is a slow feedback loop: change the pattern, re-run the program, read the output, repeat. A dedicated tester collapses that loop to milliseconds. You see matches highlight as you type, so you can build a pattern incrementally and catch mistakes the moment they happen.

The live view also makes the invisible visible. It is hard to tell from a raw pattern whether .* is being greedy, whether your character class includes the hyphen you meant, or whether the g flag is actually finding every match. Highlighting answers those questions at a glance.

Because everything runs locally in your browser, there is nothing to install and nothing to upload. That matters when your test text is a real log file, a database dump, or anything you would rather not paste into a remote server. Private data stays on your machine.

Start with the smallest pattern that could work and grow it. Enter your expression in the pattern field — no surrounding slashes needed — then paste representative sample text below it.

As you type, matches light up in the text. Watch the results panel: it shows each full match plus every capture group, numbered $1, $2, and so on, with named groups labelled by name. If a group shows undefined, that part of the pattern did not participate in the match.

Toggle flags to change behaviour: g finds all matches instead of just the first, i ignores case, and m makes ^ and $ match at line breaks. When the highlighting matches your intent across every sample line, copy the pattern into your code with confidence.

Regular expressions show up everywhere text needs structure:

• Validation — check that an email, phone number, postal code or username has the right shape before you accept it.
• Extraction — pull dates, IDs, prices or URLs out of unstructured text and logs.
• Search and replace — find every occurrence of a pattern and rewrite it, often paired with capture groups in the replacement.
• Parsing logs — split a log line into timestamp, level and message using named groups.
• Cleaning data — strip out unwanted characters, collapse whitespace, or normalise formatting.

Once your pattern is solid here, take it to a bulk Find & Replace to apply it across a whole document, or start from a description with the Regex Generator if you are not sure where to begin.

Anchor when you mean the whole string. Wrap validation patterns in ^ and $ so ^\d{5}$ matches exactly five digits — without anchors, a longer string with five digits inside it also passes.

Prefer specific classes over . A dot matches almost anything. If you want digits, write \d; if you want word characters, write \w. Narrow patterns are faster and less surprising.

Watch greedy quantifiers. .* grabs as much as it can and backtracks. Use the lazy form .*? or a negated class like [^"]* when you want to stop at the next delimiter.

Escape special characters. Dots, parentheses, plus signs and brackets have meaning in regex. To match a literal . write \..

Test the edge cases. Empty strings, extra whitespace, unicode characters and multi-line input all break naive patterns. Paste a few awkward samples and confirm the highlighting still holds.