What does this tool do?
Regex Tester runs the regular expression you write against sample text and highlights every match live as you type. Whether you are extracting emails from a log file, validating a form field, or simply learning a pattern, you can iterate quickly right in the browser.
How to use it
- Paste your text into the input area.
- Adjust the options to fit your needs.
- Copy the processed text.
See matches and groups
The tool scans your text and color-highlights each match, then lists the capturing groups (the parts in parentheses) separately, so you can confirm whether your pattern grabs the area code of a phone number or the year of a date correctly. Toggle the g (global), i (case-insensitive) and m (multiline) flags on or off to change the behaviour instantly and watch the results update.
Practical tips
Build complex patterns in small pieces: match the year with \d{4} first, then add the month. Prefer lazy quantifiers (.*?) over greedy ones (.*) to avoid over-matching. Escape special characters like the dot, parentheses and plus with a backslash when you want them literally. Everything runs in your browser, so your text is never uploaded anywhere.
Frequently asked questions
Which regex syntax does it use?
It uses JavaScript's RegExp engine, so ECMAScript syntax applies. Lookahead is supported and lookbehind works in modern browsers. Some PCRE-only features (such as \K) are not available.
Why does my expression match nothing?
The most common causes are forgetting to escape a special character (a bare dot matches any character), leaving off the g flag, and a case mismatch. Turn on the i flag and test the pattern in small chunks.
Can it freeze or loop forever?
Badly written patterns with nested quantifiers (for example (a+)+) can trigger catastrophic backtracking and slow the browser down. If that happens, simplify the groups and remove unnecessary nested repetition.
Is Regex Tester free?
Yes. Regex Tester and all 300+ tools on MagmaNex are completely free with no signup or account required.
Is my data safe?
Yes. Everything runs locally in your browser. The data you enter is never sent to a server, stored, or shared.
Does it work on mobile?
Yes. Regex Tester works on phones, tablets and desktops — no app download needed.
🔒 Privacy: everything runs in your browser, your data is never sent to a server.