Dev Tool

Regex Tester

Test and debug regular expressions with real-time match highlighting and group analysis

Expression Settings

JSON Formatter

Format and validate JSON data

URL Encoder

Encode and decode URL parameters

Base64 Encoder

Encode and decode Base64 strings

About the Regex Tester

Test and debug regular expressions (regex) instantly with our free online tool. Built with the high-performance V8 engine, it provides real-time match highlighting, group analysis, and a handy cheatsheet for common patterns. Perfect for developers, data analysts, and anyone working with complex text patterns.

  1. Enter your regex pattern into the Regex Pattern field.
  2. Select the desired flags (g, i, m, u, s) to control matching behavior.
  3. Paste your test string into the Test String area.
  4. View real-time highlights and a detailed breakdown of matches and capturing groups below.

Why Choose AllOmnitools?

Instant Feedback

Zero server lag. All regex matching and highlighting happens locally on your device for maximum speed.

100% Private

Your test data and regex patterns remain private. We never track or store your data processing information.

Regex: What to Watch Out For

Regular expressions are the right tool for pattern matching, validation, and text extraction — but they're also one of the easier ways to introduce a security vulnerability. Catastrophic backtracking (ReDoS) happens when a pattern with nested quantifiers, like (a+)+$, causes the engine to try an exponential number of combinations against crafted input, hanging the thread indefinitely.

This tester runs against the browser's V8 regex engine, which is the same engine Node.js uses. Paste your pattern and test input, and matches highlight in real-time. Testing patterns against realistic data lengths here — before dropping them into production — catches backtracking issues and logic errors in seconds rather than after an incident. The tool is local-first: your patterns and data never leave the browser.

Frequently Asked Questions

Which regex flavor does this tool use?

This tool uses the standard JavaScript (V8) regex engine, which is very similar to PCRE and the regex engines used in most modern web and backend environments.

What is "Catastrophic Backtracking"?

This occurs when a regex pattern has multiple overlapping quantifiers (like (a+)+$), causing the engine to try an exponential number of combinations. Always test your patterns with realistic data lengths.

Does this tool support global (g) and case-insensitive (i) flags?

Yes. Our tester supports the most common regex flags, including global (match all), case-insensitive, multiline (m), unicode (u), and dotAll (s) modes.

Is my data safe when using this tool?

Yes. AllOmnitools is "local-first." All regex testing happens locally in your browser using JavaScript. No data is ever sent to our servers or stored externally.

Related Tools