Regex Tester & Debugger
Test, debug, and validate regular expressions in real time using the native browser JavaScript RegExp engine. Instantly visualize highlighted matches, inspect capture groups, test multi-line strings, and copy verified patterns with 100% client-side privacy.
Test regular expressions in real time with syntax highlighting and regex capture groups. Fast client-side pattern evaluation with zero server latency.
Key Features
Explore performance capabilities engineered for in-browser execution.
How to Use This Tool
Follow these 3 simple steps to use Regex Tester directly in your browser.
Type your regular expression between the slashes or pick a pre-built preset (Email, URL, IP, Date).
Paste or write sample text to evaluate matches, capture groups, and edge cases.
Review highlighted matches in the preview window, inspect capture groups in the breakdown table, and copy results.
Interactive Regular Expression Sandbox with Live Match Highlighting
Writing and debugging complex regular expressions without real-time feedback is tedious and prone to edge-case errors. ToolDolfen Regex Tester evaluates your regex pattern against sample test strings in real time using the native V8/SpiderMonkey engine, highlighting matches, reporting index coordinates, and decomposing capture groups.
Test and verify regular expressions for email validation, phone number masks, and password complexity rules before deploying to production.
Formulate precise capture patterns to extract IP addresses, timestamps, and error codes from raw server log files.
Toggle the "g" (global) and "i" (case-insensitive) flags above the pattern box to match all occurrences regardless of casing.
Frequently Asked Questions
Clear, verified answers to common technical and workflow questions about Regex Tester.
Which regular expression engine is used?
This tool uses your browser's native ECMAScript / JavaScript RegExp engine. It fully supports standard JavaScript regex features including lookahead, lookbehind, Unicode property escapes, and named capture groups.
Are my regular expressions or test data sent to a server?
No. Regex evaluation runs entirely on your device inside your web browser. Neither your patterns nor your test strings are uploaded or logged anywhere.
How do the flag toggles work?
You can toggle flags with one click: 'g' finds all occurrences, 'i' ignores letter casing, 'm' treats each line with separate ^ and $ anchors, 's' allows dots to match newlines, and 'u' enables full Unicode code point handling.
Can I test complex multi-line text?
Yes, you can paste extensive multi-line logs, CSV snippets, or source code into the test string area to verify pattern matching across realistic documents.
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