Regex Tester & Debugger
Test and debug regular expressions online with real-time match highlighting, group capture extraction, and flag toggles client-side in the browser.
What is the Regex Tester?
The Regex Tester validates and matches regular expression patterns against test strings with live syntax highlights, match counts, and capture group breakdowns.
How to Use the Tool
- Enter your regular expression pattern and select appropriate flags (g, i, m, s, u).
- Paste or type your test string in the input area.
- View real-time highlighted match segments, match counts, and capture groups.
- Switch to substitution/replace mode to test string replacements.
Common Use Cases
- Validating email, phone number, and URL extraction patterns.
- Testing string cleanup and replacement logic before deploying code.
- Debugging complex capture groups and lookaheads in API validations.
Supported Formats & Options
Supports standard JavaScript flags (Global, Case-insensitive, Multiline, DotAll, Unicode), match indexing, group extractions, and live replacement testing.
Related Guides & Tutorials
A cheat sheet of the top 20 regular expression patterns used by developers for input validation and text extraction.
A complete developer guide to learning, writing, and testing regular expressions (Regex) in modern web development.
Learn regex syntax, character classes, lookaheads, capture groups, and common regex validation patterns across JavaScript and backend runtimes.
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Frequently Asked Questions
What regex engine does this tester use?
It uses the native JavaScript RegExp engine running directly inside your browser.
Is my test data or regex pattern sent to any server?
No. All regex compilation, matching, and replacement tests run 100% locally in your browser memory.