20 Regex Patterns Every Developer Should Know
A curated collection of the most useful regular expressions — from email validation to hex colors, with explanations you can actually understand.
The Regex Reference You Actually Need
Rather than another tutorial, this is a practical reference of patterns you'll actually use — with clear explanations of how each part works.
1. Email Address
/^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/Validates standard email format. Not RFC-compliant (there is no perfect email regex), but catches typos and common mistakes.
2. URL
/^https?:\/\/[\w\-]+(\.[\w\-]+)+[/#?=$]*/Matches http and https URLs with a hostname and optional path.
3. IPv4 Address
/^(?:(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}
(?:25[0-5]|2[0-4]\d|[01]?\d\d?)$/Validates each octet as 0–255, preventing invalid IPs like 256.0.0.1.
4. Phone Number (US)
/^\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}$/Matches (555) 123-4567, 555-123-4567, 5551234567, etc.
5. Hex Color Code
/^#?([a-fA-F0-9]{6}|[a-fA-F0-9]{3})$/Matches #FFF, #ffffff, #000, with or without the # prefix.
6. Date (YYYY-MM-DD)
/^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$/Validates year, month (01–12), and day (01–31) with proper month bounds.
7. Time (HH:MM or HH:MM:SS)
/^([01]\d|2[0-3]):([0-5]\d)(:[0-5]\d)?$/Matches 00:00 to 23:59, with optional seconds.
8. Username
/^[a-zA-Z0-9_-]{3,16}$/Alphanumeric + underscore/hyphen, 3–16 characters.
9. Strong Password
/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)
(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$/Requires: lowercase, uppercase, digit, special char, min 8 chars.
10. Credit Card (basic)
/^\d{4}[- ]?\d{4}[- ]?\d{4}[- ]?\d{4}$/Matches Visa, Mastercard format. Use a payment library for real validation.
11. Slug / URL-friendly string
/^[a-z0-9]+(?:-[a-z0-9]+)*$/Lowercase letters, numbers, single hyphens between words. No leading/trailing hyphens.
12. HTML Tag
/^<([a-z]+)([^<]+)*(?:>(.*)<\/\1>|\s+\/>)$/Matches opening tags with content and closing tags, or self-closing tags.
13. Comma-Separated Numbers
/^\d{1,3}(,\d{3})*$/Matches 1,000, 1,000,000 but not 10,00 or 1000,000.
14. UUID
/^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-
[0-9a-f]{4}-[0-9a-f]{12}$/iMatches standard UUID format (v4 or any version).
15. File Extension
/\.(jpg|jpeg|png|gif|webp)$/iExtracts image file extensions from filenames.
Test Your Regexes
Use our Regex Tester to validate patterns against test strings — with real-time highlighting of matches and capture groups.
Frequently Asked Questions
What's the best email validation regex?
For most apps: /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/. It catches 99% of typos. For the truly RFC-compliant version (5300+ characters), see the emailregex.com page — but it's unreadable and the false-negative rate is actually worse. Better strategy: send a confirmation email rather than reject valid-looking addresses.
How do I match a URL?
Simple: /https?:\/\/[\w\-]+(\.[\w\-]+)+([\/?#].*)?/. Production-grade URL parsing is a job for the URL/URI parser built into your language (URL constructor in JS, urllib in Python, java.net.URI in Java). Use regex for quick filtering, but use the parser for anything that touches user data.
Should I use regex to parse HTML?
No. Regex is the wrong tool for HTML — it can't handle nested tags, attributes with > in them, CDATA sections, or comments reliably. Use a real HTML parser: DOMParser in JS, BeautifulSoup in Python, Nokogiri in Ruby. The Stack Overflow answer that starts 'you can't parse HTML with regex' has 13,000 upvotes for a reason.