What is a regular expression?

A regular expression (regex) is a sequence of characters that defines a search pattern. It is used for pattern matching in strings — extracting data, validating input, finding and replacing text. Common uses include email validation, phone number extraction, and log file parsing.

What do regex flags like g, i, m mean?

Common regex flags: g (global) finds all matches, not just the first; i (case-insensitive) ignores uppercase/lowercase differences; m (multiline) changes ^ and $ to match line boundaries instead of string boundaries. You can combine flags like /pattern/gi.

How do I test a regex pattern?

Type your regex pattern between the forward slashes in the pattern input, add any flags you need, then type a test string. Valid matches will be highlighted instantly. Use common patterns like \d+ for digits, \w+ for word characters, and .* for any characters.

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Developer

Regex Tester

Test and debug regular expressions with real-time matching.

Quick Answer & Summary

The Regex Tester is a fast, accurate Developer utility designed to test and debug regular expressions with real-time matching. entirely in your browser with zero server data storage.

Pattern

Enter your regular expression

Flags

Global (g)

Case Insensitive (i)

Multiline (m)

Test String

Enter text to test against the pattern

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Toolbox Editorial TeamVerified Authors

Systems & Security Engineers • Applied Cryptography & High-Performance Web Tools

Updated: August 2026

100% In-BrowserZero server storage

Standards AuditedRFC & ISO compliant

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Documentation & Guide

How to Use Regex Tester

Enter regex pattern

Type your regular expression in the input field.

Enter test string

Paste or type the text you want to test against.

View matches

See highlighted matches in real-time.

Pro Tips

Use flags for case-insensitive matching

Test edge cases

Practical Examples & Conversions

Input

[a-z]+@[a-z]+\.[a-z]+

Output

Matches: test@example.com

Frequently Asked Questions (PAA)

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Authoritative Standards & Citations

Calculations and algorithms on this page are implemented and verified in strict accordance with the following official technical specifications:

IETF (Internet Engineering Task Force)

RFC 7519: JSON Web Token (JWT)

Standardized compact, URL-safe means of representing claims to be transferred between two parties.

W3C Recommendation

Web Cryptography API Specification

Standard JavaScript API for performing basic cryptographic operations in web applications.

IETF Standards Track

RFC 4122: A Universally Unique IDentifier (UUID) URN Namespace

Definition of uniform format and generation algorithms for UUIDs.