FluxToolkit
Developer Utilities

Regex Pattern Library

A curated collection of production-ready regular expressions. Click any pattern to open it directly in our interactive sandbox and test it against your own strings.

Interactive Regex Sandbox

Need to write your own custom regex? Use our free sandbox tool to write, test, and debug your patterns with visual highlight capture groups and AI generation.

Open Sandbox

Browse Patterns

Network Patterns

Match IPv4 Address Regex

A regular expression to validate and extract standard IPv4 IP addresses from logs or text.

/^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/gm
Web Development

Match Hex Color Code Regex

A regex pattern to identify valid 3-digit and 6-digit hexadecimal color codes used in CSS.

/^#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$/gmi
Data Validation

Match Credit Card Number Regex

A regex pattern to detect major credit card providers (Visa, MasterCard, Amex, Discover).

/^(?:4[0-9]{12}(?:[0-9]{3})?|5[1-5][0-9]{14}|3[47][0-9]{13}|6(?:011|5[0-9][0-9])[0-9]{12})$/gm
Network Patterns

Match MAC Address Regex

A regex pattern to validate standard IEEE 802 MAC addresses separated by colons or hyphens.

/^([0-9A-Fa-f]{2}[:-]){5}([0-9A-Fa-f]{2})$/gm
Web Development

Match HTML Tags Regex

A regex pattern to extract or strip HTML elements from a block of text.

/<\/?\w+((\s+\w+(\s*=\s*(?:".*?"|'.*?'|[^'">\s]+))?)+\s*|\s*)\/?>/g

What Are Regular Expressions (Regex)?

A Regular Expression (often abbreviated as regex or regexp) is a sequence of characters that specifies a search pattern in text. Usually, such patterns are used by string-searching algorithms for "find" or "find and replace" operations on strings, or for input validation.

It is a technique developed in theoretical computer science and formal language theory that has become a fundamental tool for modern software developers. Whether you are validating a user's email address in a web form, parsing massive server logs, or building a web scraper, regular expressions allow you to identify complex patterns with a single line of code.

Why Use a Pattern Library?

Regex syntax is notoriously dense and difficult to read (often described playfully as a "write-only language"). Trying to manually write a pattern to validate an IPv4 address or an HTML tag from scratch is prone to errors—specifically, edge cases that can bypass your validation or cause catastrophic backtracking that crashes your server.

Our Regex Pattern Library provides tested, production-ready patterns for the most common developer use cases. Every pattern in this library can be instantly loaded into our Sandbox, allowing you to test it against your own specific edge cases before you deploy it to production.

Language Flavors

While the basic syntax of regular expressions is almost universal, different programming languages implement slightly different "flavors" of the engine. The most common flavor is PCRE (Perl Compatible Regular Expressions), which heavily influenced PHP, Ruby, and Java.

JavaScript uses the ECMAScript standard, which historically lacked some advanced features (like lookbehinds) but has caught up in recent years. Python uses its own re module, and Golang uses the RE2 engine (which sacrifices advanced features like lookarounds in exchange for guaranteed linear execution time to prevent DDoS attacks).

When using the patterns from our library, always verify them in the sandbox using the specific engine flavor that matches your backend architecture!