Regex Tester
Test regular expressions against strings in real time. See highlighted matches, capture groups, and perform find-and-replace operations. All processing happens locally in your browser.
Pattern & Flags
Find & Replace
How It Works
This tool uses JavaScript's built-in RegExp engine to test your regular expressions in real time. As you type a pattern and test string, the tool instantly evaluates matches, highlights them, and displays capture groups.
The replacement feature uses String.prototype.replace(), supporting backreferences like $1, $2 for captured groups. All processing runs entirely in your browser with no server communication.
Common Regex Patterns
- Email:
[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,} - URL:
https?:\/\/[^\s]+ - IP Address:
\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b - Phone Number:
\+?\d{1,3}[-.\s]?\(?\d{1,4}\)?[-.\s]?\d{1,4}[-.\s]?\d{1,9} - HTML Tag:
<([a-z]+)([^<>]*)>(.*?)<\/\1>
Frequently Asked Questions
What is a regular expression?
A regular expression (regex) is a sequence of characters that defines a search pattern. It is used for pattern matching within strings, enabling tasks like validation, searching, and text replacement.
What do regex flags do?
Flags modify how the regex engine interprets the pattern. Common flags include: g (global - find all matches), i (case-insensitive), m (multiline - ^ and $ match line boundaries), s (dotAll - dot matches newlines), and u (unicode - enables full Unicode support).
What are capture groups?
Capture groups are portions of a regex pattern enclosed in parentheses. They capture the matched text so it can be referenced later, for example in replacement strings using $1, $2, etc.
Is my data processed on a server?
No. All regex matching and replacement happens entirely in your browser using JavaScript. Your data never leaves your device.