What regex features are supported?

This tester supports JavaScript regular expressions, including character classes, quantifiers, alternation, capture groups, lookahead/lookbehind (in modern browsers), and all regex flags (g, i, m, s, u, y).

How do I test case-insensitive matching?

Add the "i" flag to the Flags field. For example, pattern "hello" with flag "i" will match "Hello", "HELLO", "hElLo", etc.

How do I use capture groups?

Put part of your pattern in parentheses: (\w+)@(\w+)\.com creates two capture groups for email username and domain.

Can I use this with my code editor?

Yes! Test patterns here first, then copy them directly into your JavaScript, Python, or other language where regex is supported.

How do I use this with ChatGPT or Claude?

Share this URL with AI models to have them help build or debug regex patterns: "Explain why this regex works: [pattern]"

What is the difference between g, m, and i flags?

g = global (find all matches), i = case-insensitive, m = multiline (^ and $ match line breaks not just string start/end).

Can I test lookahead and lookbehind?

Yes, if your browser supports them. Positive lookahead: (?=pattern), negative lookahead: (?!pattern), and similar for lookbehind.

Why does my pattern not work?

Check: (1) escaping (use \\ for backslash), (2) character classes ([a-z] vs \w), (3) quantifiers (+, *, ?), and (4) anchors (^ and $).

REGEX

Regex Tester

Revision: April 15, 2026 • Test regex patterns against sample text

Build and validate regular expressions

Enter a regex pattern and sample text to see matches in real time. This tool helps you debug patterns, check flags, and view captured groups before using the regex in code or search tools.

Pattern

Regex pattern Flags Sample text

Results

🔒 Why This Tool Works in Your Browser

Regular expression testing involves analyzing text patterns and testing matching rules—operations that don't require external processing but that could reveal sensitive information about your data patterns. Uploading test data to cloud regex tools exposes what you're searching for, what patterns you're analyzing, and what data structure you're working with. Browser-based regex testing keeps your test samples and pattern analysis completely private. This matters especially for developers working on proprietary parsing logic, security researchers analyzing potentially malicious content, or professionals handling sensitive data. Local testing means writing regex patterns, testing against sample data, and debugging matches entirely on your device without external visibility. You can test patterns against confidential datasets—customer records, financial data, personal information—knowing your test samples never touch external servers. Cloud regex testers could log every pattern you test and every sample data point, creating profiles of what data you process. Local testing eliminates this surveillance. Your regex development process, data structure insights, and parsing logic remain completely confidential. This preserves development autonomy and protects proprietary parsing strategies from exposure. Whether you're building data extraction systems, security detection rules, or text processing pipelines, local regex testing keeps your approach private and your data confined to your machines.