Regex Tester: Test & Debug Regular Expressions | Morph

A regex tester lets you write a regular expression, paste in sample text, and instantly see what it matches — with the matches highlighted right in your text. Regular expressions are powerful but notoriously easy to get wrong, and the fastest way to get one right is to test it against real input as you build it. Morph's regex tester does exactly that, live, in your browser.

Instead of running your pattern in code, restarting, and squinting at the output, you tweak the expression and watch the highlights update in real time. When a match appears or disappears, you know immediately whether your last change helped.

What you get

Live match highlighting over your sample text as you edit the pattern.
Capture group breakdown, so you can see exactly what each group `(...)` pulled out.
Flag toggles for global, case-insensitive, multiline, and other common modifiers.
Instant feedback on invalid patterns, so a stray bracket or quantifier is caught right away.
A scratchpad for real input — paste logs, CSV rows, URLs, or any text you actually need to match.

Why test regex in the browser

Regex is a write-and-verify loop: you rarely nail a non-trivial pattern on the first try. A dedicated tester collapses that loop to nothing — change the pattern, see the result. Doing it in a browser tab means you don't have to drop into a REPL or write a throwaway script just to check whether your character class is doing what you think.

It's also private, which matters more for regex than people expect. The text you're matching against is often real data — production log lines, customer records, internal file paths. Morph's regex tester runs entirely client-side, so that sample text never leaves your browser. Nothing is uploaded, and there's no account to create.

Build patterns with confidence

Start simple and grow the pattern piece by piece, watching the highlights confirm each step. Use capture groups to pull out the parts you care about — a date, an ID, a domain — and check the group breakdown to make sure each one captures the right slice. Toggle flags to handle case or to scan across multiple lines. When the pattern matches exactly what you intend and nothing you don't, copy it into your code, your editor's find-and-replace, or your command-line tool.

For working with structured data once you've extracted it, the JSON formatter pairs well, and the markdown editor is handy when you're documenting the patterns you've built. The regex tester is the place to get the expression right before it ships.

How to use

Open the regex tester — Go to the regex tester page. The pattern field and a sample-text area load instantly in your browser — no sign-up required.
Enter your pattern — Type your regular expression into the pattern field. Invalid syntax is flagged immediately so you can fix it on the spot.
Paste your test text — Paste the text you want to match against — log lines, CSV rows, URLs, or any real input. Matches highlight as you type.
Set your flags — Toggle flags like global, case-insensitive, and multiline to control how the pattern is applied to your text.
Check capture groups — Review the capture group breakdown to confirm each group pulls out the right piece, then copy the finished pattern into your code.

Frequently asked questions

Is this regex tester free?

Yes. You can build and test regular expressions in your browser for free, with no account or sign-up required.

Is my test text uploaded anywhere?

No. The tester runs entirely client-side in your browser. The pattern and the sample text you paste stay on your own device and are never sent to a server.

What regex flavor does it use?

It uses JavaScript regular expressions, the same engine that runs in browsers and Node.js. Most common syntax — character classes, quantifiers, groups, lookaheads — works as expected.

Can I see what each capture group matched?

Yes. The tool breaks down capture groups so you can confirm exactly what each parenthesized group extracted from your text.

Why isn't my pattern matching?

Common causes are a missing flag (such as case-insensitive or multiline), an unescaped special character, or a greedy quantifier grabbing too much. The live highlighting and invalid-pattern warnings help you spot which one it is.