Regex Tester & Helper

This regex tester runs your pattern with the browser’s built-in JavaScript RegExp engine. Type a regular expression at the top, paste test text below, and every match is highlighted live, with a running match count. The Match Details list shows each match, its index range in the text (for example Index: 12-27) and the value of every capture group (Group 1, Group 2…), so you can see at a glance whether your parentheses capture what you think they capture.

Toggle the g flag to find all matches (without it, only the first match is returned), i to ignore case, and m for multiline mode, where ^ and $ match at the start and end of each line. If the pattern is invalid, such as an unbalanced parenthesis or a quantifier with nothing to repeat, the tool shows the browser’s syntax error message instead of silently returning nothing, and re-runs as soon as you fix it.

Five presets give you a starting point: email address, Taiwan mobile number (10 digits starting with 09), IPv4 address (each octet 0–255), Taiwan national ID format, and a strong-password check (at least 8 characters with uppercase, lowercase and a digit). One click loads the pattern, flags and sample text so you can adapt it. Note that the ID preset only checks the shape, one letter, then 1 or 2, then eight digits, and does not verify the checksum digit; the email pattern is a practical approximation, not the full RFC grammar.

Because it uses JavaScript syntax, it is ideal for front-end form validation, Node.js scripts and browser extensions. Most basics carry over to Python, PHP (PCRE), Java or SQL, but some advanced features such as possessive quantifiers, atomic groups or the \A and \Z anchors are engine-specific, so results can differ. All matching happens in your browser; your test text is never uploaded.