Regex Tester

The browser's native RegExp engine, which makes it a true javascript regex tester. Most syntax carries over to Python, Go, or Java, but details like lookbehind support and named groups vary, so confirm in your target language before shipping.

Both. Invalid patterns trigger an error message from the engine, and valid ones are executed against your test string with every match, offset, and capture group listed below.

Usually a greedy quantifier. Constructs like .+ expand as far as they can, so tighten the character class, add anchors, or switch to the lazy form .+? and watch the match list shrink.

Yes. Paste the whole block into the test string, then enable multiline if you anchor per line, or dotAll if your pattern needs the dot to walk over newline characters.

It's the zero-based character offset where the match starts in your test string. That number maps directly to what String.prototype.slice or substring would use in code.

No. Pattern matching executes locally in your browser, so proprietary logs or user data in the test string never touch a server.

No. Patterns that can match an empty string, like a lone \d*, are stepped past automatically, so the match list finishes instead of looping forever.

You see matches the instant you type, with no compile and run loop. As a regular expression tester it runs your pattern against the test string live, highlighting each hit with its index and capture groups. Being an online regular expression tester, there's nothing to install and your text stays in the browser.

Yes. Type an invalid pattern and the regex validator surfaces the engine's error message in red before you run anything. A valid pattern instead lists its matches, so the same field validates and tests in one step.

That's the whole idea. As a regex validator online it runs in the browser, and whether you call it a regular expression validator or a regular expression validator online, the job is the same: confirm the pattern compiles, then see what it matches.

No boilerplate. This online regex tester skips the file, the imports, and the print statements; you paste a pattern and a sample and read the results. That tight loop is the whole appeal.

Yes. Working with regex online here, you paste the pattern and sample text and get an instant verdict, so it's a fast regex checker for confirming behavior before the pattern lands in code.

Paste your pattern, then drop genuine samples into the Test string box, including lines that shouldn't match. To check regex online this way shows every hit with its offset, and to check regular expression online against edge cases you just add more lines and watch the match list react.

No, and it's fair to be clear about it: this page tests and validates patterns rather than generating them. A regex generator online would build a pattern from a description, which is a different tool. Here you write or paste the expression, and the live matches tell you whether it's right.

Yes. Every match lists Group 1, Group 2, and so on, so as a regex pattern validator it proves not just that the pattern matched but what each part grabbed. That group breakdown is what makes a complex pattern debuggable.

It is. As an online regex evaluator the matches recompute on every keystroke, and being a plain regex evaluator too, it lists each hit with its index the moment the pattern is valid.

Watch the match list as you tighten the pattern. A regular expression checker like this highlights exactly what a greedy quantifier swallowed, so to debug regex online you shrink the character class or switch to a lazy quantifier and see the matches shrink in real time.