Regex Tester
Test, validate, and debug regular expressions instantly with real-time match highlighting.
Regular Expression
Features
- Match Highlighting: See exactly what your Regular Expression matches in real-time with visual highlighting inside your test string.
- Replace Testing: Instantly preview how a substitution string (like
$1) alters your text based on the matched groups. - Common Examples: 1-click loading for frequently used regex patterns including Email Validation, URLs, and IPv4 Addresses.
- Flag Toggles: Easily swap between global (
g), case-insensitive (i), and multiline (m) matching. - Zero Latency: Because everything runs natively in your browser using JavaScript's Regex engine, feedback is instant as you type.
How it works
A Regular Expression (Regex) is a sequence of characters that specifies a search pattern. They are incredibly powerful for parsing text, validating user input, and finding/replacing strings in code.
Simply enter your pattern in the top input box (don't include the surrounding slashes, we handle that for you), define your flags (e.g. g for global matching), and type your test string below. The output will immediately highlight every match. Switch to the Replace tab to test substitution operations!
Frequently Asked Questions
Everything you need to know about DevToolkit.
Which Regex Engine does this use?
This tool uses the native JavaScript RegExp engine running directly inside your browser. Therefore, it perfectly simulates how a regex will behave when executed in Node.js, Next.js, or any modern web application.
Why doesn't my match show up unless I add the 'g' flag?
Without the 'g' (global) flag, a regular expression stops searching after it finds the very first match. Adding the 'g' flag tells the engine to find all possible matches in the entire string.
Can I test substitution groups?
Yes! In the Replace tab, you can use standard JavaScript replacement patterns like $1, $2, etc., to reference capture groups defined in your regex pattern (using parentheses).