Regex Tester
Enter a regular expression and some test text below — matches are highlighted live and listed with their exact position as you type.
How to Use the Regex Tester
- Type your regular expression pattern into the "Regular Expression" field (without the surrounding slashes).
- Set flags —
gfor global (find all matches),ifor case-insensitive,mfor multiline, and so on. - Paste or type your sample text into the "Test String" box.
- Matches are highlighted live in the preview and listed below with their index position in the string — no button to click, results update as you type.
Why Use This Tool?
Is my text or pattern uploaded anywhere?
No. The regex engine used is your browser's own native RegExp implementation — the same one that powers String.match in JavaScript everywhere. Everything runs locally; nothing you type is sent to a server, which matters if your test string includes log lines, emails or other data you'd rather keep private.
What happens if my regex is invalid?
If the pattern or flags you enter are not valid (for example, mismatched parentheses or an unsupported flag combination), the tool catches the SyntaxError from RegExp and displays a clear message above the preview instead of silently failing.
Why does the "g" flag matter for the match list?
Without the global (g) flag, JavaScript's matching only finds the first match in the string. With g set, the tool uses matchAll to find and highlight every occurrence, along with each one's starting index — essential when testing patterns meant to match repeatedly across a larger block of text.
Who uses a regex tester?
Developers validating form input patterns, data engineers writing log-parsing rules, and anyone learning regular expressions who wants immediate visual feedback on what a pattern actually matches, rather than guessing and re-running code.