Write, test, and debug JavaScript regular expressions in real-time. Enter your pattern and test string, see matched results highlighted instantly — all processing happens in your browser with zero uploads.
Every match is highlighted directly in your test string as you type. No need to click "test" — results update instantly so you can iterate quickly.
Supports all JS regex flags (g, i, m, s, u, y) and features including lookahead, lookbehind, named capture groups, and Unicode property escapes.
Sensitive patterns or proprietary data never leave your browser. No server-side logging — your regex stays entirely local.
/^[\w.-]+@[\w.-]+\.\w{2,}$/
Validates basic email format. Works for most common use cases — [email protected]
/https?:\/\/[\w.-]+\.[\w]{2,}\/?/
Matches HTTP and HTTPS URLs from text. Great for parsing links out of raw content.
/^\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}$/
Matches US phone numbers in multiple common formats: (555) 123-4567, 555-123-4567, etc.
This tester uses JavaScript's built-in RegExp engine, which supports the ECMAScript specification. Most common patterns work across JavaScript and PCRE, but some advanced features differ (like recursive patterns).
The tool supports all standard JavaScript flags: g (global), i (case-insensitive), m (multiline), s (dotAll), u (unicode), and y (sticky). Toggle any combination.
Yes. The test runs entirely in your browser, so the limit is your browser's memory. For extremely large documents, consider breaking them into sections.
ByteBox is 100% client-side — your regex patterns never touch a server. It also integrates with ByteBox's other developer tools like JSON Formatter and Text Diff Checker for related workflows.