Biblioteca de Regex

Curated Regular Expression Patterns for Common Validation

Writing correct regular expressions from scratch is time-consuming and error-prone — email validation alone has dozens of edge cases around quoted local parts, internationalized domain names, and RFC 5322 compliance that most ad-hoc patterns miss. The Regex Library provides a browsable collection of production-tested patterns organized by category, each with clear documentation of what it matches, what it intentionally excludes, and example strings for both positive and negative cases.

Every pattern in the library has been validated against real-world edge cases and includes a one-click copy feature. Patterns cover common validation needs including email addresses, URLs, UUIDs, IP addresses (v4 and v6), phone numbers, dates, hex colors, credit card formats, slugs, and semantic versions. Each entry explains the regex fragment by fragment so you understand what you are copying rather than using it as a black box.

Identity and Communication Patterns

Patterns for validating user identity and communication fields:

• Email (RFC 5322 simplified): Validates standard email formats with domain validation, rejecting obvious invalid inputs while allowing legitimate edge cases like plus-addressing
• Phone (E.164 international): Matches international phone numbers with country code prefix
• URL (HTTP/HTTPS): Validates web URLs with optional query strings and fragments
• Domain name: Validates hostnames including subdomains and TLDs
• Slug: Validates URL-safe slugs (lowercase letters, numbers, hyphens)

Each pattern includes notes on intentional limitations — for example, the email pattern does not validate that the domain's MX record exists, only that the format is structurally valid.

Identifier and Format Patterns

Patterns for validating technical identifiers and data formats:

• UUID v4: Matches the canonical 8-4-4-4-12 format with correct version digit
• IPv4 address: Validates dotted-quad notation with octet range checking (0-255)
• IPv6 address: Handles full notation, compressed (::) notation, and mixed IPv4/IPv6
• MAC address: Matches colon-separated and dash-separated hardware addresses
• Hex color: Validates 3-digit and 6-digit CSS hex color codes with optional # prefix
• Semantic version: Matches semver with optional pre-release and build metadata
• JWT token: Validates the three-part base64url structure of JSON Web Tokens

Using Patterns Safely

Best practices when using regex patterns from a library:

• Understand before copying: Read the fragment explanation to know what edge cases are and are not covered
• Test with your data: Every application has unique input patterns — test the regex against your actual user input samples
• Add anchors: Use ^ and $ to prevent partial matches when validating complete strings
• Consider performance: Some patterns with alternation or backtracking behave poorly on very long inputs — test with maximum expected input length
• Complement with logic: Regex validates format, not semantics — an email that matches the pattern may still not exist, an IP that matches may not be routable

The library clearly marks which patterns are suitable for strict validation (rejecting invalid input) versus lenient extraction (finding patterns within larger text).

Code Examples

Common Validation Patterns

// Email (simplified RFC 5322)
const emailRegex = /^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/;

// UUID v4
const uuidV4Regex = /^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i;

// IPv4 with range validation
const ipv4Regex = /^(?:(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(?:25[0-5]|2[0-4]\d|[01]?\d\d?)$/;

// Semantic Version (semver)
const semverRegex = /^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-((?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+([0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$/;

// CSS Hex Color (3 or 6 digits)
const hexColorRegex = /^#([0-9A-Fa-f]{3}|[0-9A-Fa-f]{6})$/;