Commonly Used Regular Expressions Cheat Sheet

A practical collection of regex patterns for common validation and matching tasks. Test each pattern live using the linked regex tester.

1. Digits & Numbers

• Whole Numbers
  /^\d+$/
  Test →

• Decimal Numbers
  /^\d*\.\d+$/
  Test →

• Whole + Decimal Numbers
  /^\d*(\.\d+)?$/
  Test →

• Negative, Positive Whole + Decimal
  /^-?\d*(\.\d+)?$/
  Test →

• Whole + Decimal + Fractions
  /[-]?[0-9]+[,.]?[0-9]*([\/][0-9]+[,.]?[0-9]*)*/
  Test →

2. Alphanumeric

• Alphanumeric (no spaces)
  /^[a-zA-Z0-9]*$/
  Test →

• Alphanumeric (with spaces)
  /^[a-zA-Z0-9 ]*$/
  Test →

3. Email Addresses

• Common Email Format
  /^([a-zA-Z0-9._%-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,6})*$/
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• More Flexible (uncommon emails)
  /^([a-z0-9_\.\+-]+)@([\da-z\.-]+)\.([a-z\.]{2,6})$/
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4. Password Strength

• Complex (≥8 chars, 1 lowercase, 1 uppercase, 1 number, 1 special)
  /(?=(.*[0-9]))(?=.*[\!@#$%^&*()\\[\]{}\\-_+=~|:;"'<>,./?])(?=.[a-z])(?=(.[A-Z]))(?=(.*)).{8,}/`
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• Moderate (≥8 chars, 1 lowercase, 1 uppercase, 1 number)
  /(?=(.*[0-9]))((?=.*[A-Za-z0-9])(?=.*[A-Z])(?=.*[a-z]))^.{8,}$/
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5. Username

• Alphanumeric + _ - (3–16 characters)
  /^[a-z0-9_-]{3,16}$/
  Test →

6. URLs

• With http(s) protocol
  /https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/
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• Protocol optional
  /(https?:\/\/)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/
  Test →

7. IP Addresses

• IPv4
  /^(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])$/
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• IPv6 (full pattern — very long)
  (See full pattern in original source)
  Test →

• IPv4 or IPv6
  (Combined pattern — see source for complete regex)
  Test →

8. Dates

• YYYY-MM-DD
  /([12]\d{3}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01]))/
  Test →

• DD-MM-YYYY (with -, ., / separators)
  (See full pattern in source)
  Test →

• DD-mmm-YYYY (month names)
  (See full pattern in source)
  Test →

9. Time Formats

• HH:MM 12-hour (optional leading zero)
  /^(0?[1-9]|1[0-2]):[0-5][0-9]$/

• HH:MM 12-hour with AM/PM
  /((1[0-2]|0?[1-9]):([0-5][0-9]) ?([AaPp][Mm]))/

• HH:MM 24-hour (leading zero)
  /^(0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/

• HH:MM 24-hour (optional leading zero)
  /^([0-9]|0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]$/

• HH:MM:SS 24-hour
  /(?:[01]\d|2[0123]):(?:[012345]\d):(?:[012345]\d)/

10. HTML & JavaScript

• HTML Tags (with/without attributes)
  /<\/?[\w\s]*>|<.+[\W]>/
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• Inline JS Event Handlers
  /\bon\w+=\S+(?=.*>)/
  Test →

11. Slug

• URL-friendly slug
  /^[a-z0-9]+(?:-[a-z0-9]+)*$/
  Test →

12. Find Duplicates in String

• Repeated words
  /(\b\w+\b)(?=.*\b\1\b)/
  Test →

13. Phone Numbers

• International Phone Numbers (with optional country code / extension)
  /^(?:(?:\(?(?:00|\+)([1-4]\d\d|[1-9]\d?)\)?)?[\-\.\ \\\/]?)?((?:\(?\d{1,}\)?[\-\.\ \\\/]?){0,})(?:[\-\.\ \\\/]?(?:#|ext\.?|extension|x)[\-\.\ \\\/]?(\d+))?$/
  Test →

Important: Prefer using a proper phone validation library instead of regex when possible.

Additional Patterns

• Zip / Postal Codes
  No universal regex exists. Use country-specific patterns: See list

• Credit Card Numbers
  Common card patterns

• Social Security Number (US SSN)
  /^((?!219-09-9999|078-05-1120)(?!666|000|9\d{2})\d{3}-(?!00)\d{2}-(?!0{4})\d{4})|((?!219 09 9999|078 05 1120)(?!666|000|9\d{2})\d{3} (?!00)\d{2} (?!0{4})\d{4})|((?!219099999|078051120)(?!666|000|9\d{2})\d{3}(?!00)\d{2}(?!0{4})\d{4})$/

• Passport Number (basic pattern)
  /^[A-PR-WY][1-9]\d\s?\d{4}[1-9]$/

Useful References

• Regular-Expressions.info
• RegexLib
• RegexHub
• Smashing Magazine – Advanced Regex
• Tuts+ – 8 Regex You Should Know

Happy regexing! 🚀