Regex Tester

Test, validate, and debug regular expressions with real-time highlighting

Regular expressions (regex) are powerful tools for pattern matching and text validation. Whether you're validating email addresses, extracting data from logs, or parsing complex strings, our Regex Tester helps you build and debug patterns with real-time feedback, match highlighting, and a comprehensive patterns library — all securely in your browser.

How to Use the Regex Tester

Our Regex Tester makes it easy to build, test, and debug regular expressions. Here's how to use it:

Enter your pattern – Type your regular expression between the forward slashes (e.g., /pattern/).
Set flags – Toggle flags like g (global), i (case-insensitive), m (multiline), and others to modify matching behavior.
Add test text – Enter the text you want to test your regex against.
Test automatically – The tool updates in real-time as you type, highlighting matches instantly.
View highlighted matches – See exactly where your pattern matches in the highlighted text area.
Review match details – The matches list shows each match with its position and capture groups.
Use pattern library – Click any common pattern to load it instantly.

Real-Time Testing

Instant feedback as you type

Match Highlighting

See matches visually

Detailed Results

Match positions & groups

Pattern Library

Common regex patterns

Regular Expression

Pattern

/ /

g global

i case-insensitive

m multiline

s dot all

u unicode

y sticky

Test String

Match Results

Matches

Groups

Unique

Highlighted Matches

All Matches

No matches found

Common Regex Patterns

Regular expressions (regex) are patterns used to match character combinations in strings. Use the flags to modify matching behavior: g (global), i (case-insensitive), m (multiline).

Regex Testing Disclaimer

The Regex Tester provided by Easy Tools HQ is for development, testing, and educational purposes only. All regex operations are performed locally in your browser — no pattern or test data is sent to our servers.

Important limitations: Regular expression engines can behave differently across programming languages and platforms. This tool uses JavaScript's RegExp engine, which may not support all features available in other languages (PCRE, Python, Java, etc.).

Cross-language compatibility: Patterns that work in this JavaScript-based tester may:

Not work in other languages (Python, PHP, Java, C#, etc.)
Have different performance characteristics in production environments
Behave differently with Unicode across platforms
Require escaping adjustments for different regex dialects
Support different flag sets than JavaScript provides

Catastrophic backtracking warning: Poorly constructed regular expressions can cause exponential backtracking, leading to browser performance issues or freezing. This is especially risky with nested quantifiers like `(a+)+` or `(a*)*`. Test with realistic data sizes.

Sensitive data warning: Do not test regex patterns on sensitive production data (passwords, PII, authentication tokens) in any online tool. All processing is local, but browser extensions or compromised networks could potentially expose your data.

Group highlighting: Group capture highlighting is simplified in this tool and may not accurately represent nested or complex group structures. Always verify group indices in your target language.

Last Updated: March 2026

JavaScript engine • Test before production • Local processing