Regex Tester Online
Test and debug regular expressions with real-time match highlighting.
What Is a Regex Tester?
Regex Tester is a free online tool that test and debug regular expressions with real-time match highlighting. No files are uploaded — everything is processed locally on your device.
This regex tester online lets you write and evaluate regular expressions against sample text in real time, highlighting all matches as you type. Regular expressions are powerful patterns used in programming for text search, validation, extraction, and replacement. Our tester supports JavaScript regex syntax with all standard flags (g, i, m, s, u) and provides match details including capture groups. Everything runs locally in your browser for privacy.
Privacy guarantee: Regex Tester processes all files directly in your browser using WebAssembly. No data is uploaded to any server, no information is collected, and the tool works offline after loading. Unlimited usage with no signup, no watermarks, and no file size limits.
How to Use Regex Tester
Enter your regex pattern
Type a regular expression pattern in the pattern field.
Set flags
Toggle regex flags like global (g), case-insensitive (i), or multiline (m) as needed.
Paste test text
Enter or paste the text you want to test against your pattern.
Analyze matches
See all matches highlighted in the text with capture group details listed below.
Why Use Our Regex Tester?
Frequently Asked Questions
Which regex flavor does this tester support?
The tester uses JavaScript's built-in RegExp engine, which supports standard syntax including lookaheads, lookbehinds (in modern browsers), character classes, quantifiers, and all standard flags.
What do the different regex flags do?
The global flag (g) finds all matches. Case-insensitive (i) ignores letter casing. Multiline (m) makes ^ and $ match line starts and ends. Dotall (s) makes the dot match newlines. Unicode (u) enables full Unicode matching.
Can I see the capture groups from my regex matches?
Yes. The tester displays all capture groups for each match with their index positions, making it easy to debug complex extraction patterns.
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