Regex Cheat Sheet: 20 Essential Patterns Every Developer Needs
Stop Googling the same regex patterns. Here are 20 battle-tested patterns you'll use again and again — copy, paste, and test them live.
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Open Regex Tester →Validation Patterns
1. Email Address
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
Matches standard email formats. Covers 99% of real-world addresses. For strict RFC 5322 compliance, the pattern is much more complex — but this handles practical validation.
2. URL (HTTP/HTTPS)
^https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)$
Matches HTTP and HTTPS URLs with optional www prefix, domain, and path/query parameters.
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 proper IPv4 format with each octet between 0-255. Rejects values like 999.999.999.999.
4. IPv6 Address (Simplified)
^([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}$
Matches full-form IPv6 addresses (8 groups of hex digits). Does not handle compressed notation (::).
5. Phone Number (International)
^\+?[1-9]\d{1,14}$
E.164 format — the international standard. Optional + prefix, 1-15 digits. Works for any country.
6. US Phone Number
^\(?([0-9]{3})\)?[-.\s]?([0-9]{3})[-.\s]?([0-9]{4})$
Matches (555) 123-4567, 555-123-4567, 555.123.4567, and 5551234567.
Data Format Patterns
7. Date (YYYY-MM-DD)
^\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])$
ISO 8601 date format. Validates month (01-12) and day (01-31) ranges, though doesn't check month-specific day limits.
8. Time (24-hour HH:MM:SS)
^([01]\d|2[0-3]):([0-5]\d):([0-5]\d)$
24-hour time format. Hours 00-23, minutes and seconds 00-59.
9. Hex Color Code
^#([0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})$
Matches #FFF, #FF5733, and #FF573380 (with alpha). Covers 3, 6, and 8-character hex codes.
10. UUID v4
^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$
Strictly validates UUID version 4 format: the third group starts with 4, the fourth starts with 8, 9, a, or b.
Text Processing Patterns
11. HTML Tags
<([a-z][a-z0-9]*)\b[^>]*>(.*?)<\/\1>
Matches paired HTML tags with content. Captures the tag name and inner content. Note: regex isn't ideal for complex HTML parsing — use a DOM parser for production code.
12. Strip HTML Tags
<[^>]+>
Matches any HTML tag for removal. Use with replace to strip all tags from a string.
13. Whitespace Trimming
^\s+|\s+$
Matches leading and trailing whitespace. Use with replace to trim strings.
14. Duplicate Words
\b(\w+)\s+\1\b
Finds repeated consecutive words like "the the" or "is is". Great for proofreading.
Password & Security Patterns
15. Strong Password
^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$
Requires at least 8 characters with one lowercase, one uppercase, one digit, and one special character. Uses lookaheads for each requirement.
16. Credit Card Number (Basic)
^\d{4}[-\s]?\d{4}[-\s]?\d{4}[-\s]?\d{4}$
Matches 16-digit card numbers with optional dashes or spaces between groups. For real validation, use the Luhn algorithm.
Code & Development Patterns
17. Semantic Version (SemVer)
^(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-]+)*))?$
Official SemVer regex. Matches versions like 1.0.0, 2.1.3-beta.1, 3.0.0-alpha+build.123.
18. File Extension
\.([a-zA-Z0-9]+)$
Captures the file extension from a filename or path. Group 1 contains the extension without the dot.
19. CSS Property-Value Pair
([a-z-]+)\s*:\s*([^;]+);
Extracts CSS property names and values. Group 1 = property, Group 2 = value.
20. Import/Require Statements
(?:import|require)\s*\(?['"]([^'"]+)['"]\)?
Matches JavaScript/TypeScript import and require statements. Group 1 captures the module path.
How to Use These Patterns
- Copy the pattern you need from above
- Open our regex tester and paste it in the pattern field
- Add test strings — both valid and invalid examples — to verify behavior
- Adjust flags (global, case-insensitive, multiline) as needed for your use case
- Integrate into your code once you've confirmed it works correctly
Important Caveats
These patterns cover the vast majority of real-world cases, but keep in mind:
- Email validation via regex is inherently imperfect. The RFC allows absurdly complex addresses. For production, use a library or send a verification email.
- Phone number formats vary wildly by country. Use a library like libphonenumber for serious phone validation.
- Don't parse HTML with regex for anything complex. Use a proper DOM parser.
- Always test edge cases: empty strings, very long inputs, Unicode characters, and boundary conditions.
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Frequently Asked Questions
What are the most useful regex patterns?
The top 5 most-used regex patterns: email validation, URL matching, phone number validation, IP address matching, and date format validation. Our cheat sheet includes 20 copy-paste patterns with live testing links.
How do I learn regex quickly?
Start with 3 concepts: character classes (\d, \w, \s), quantifiers (*, +, ?, {n}), and anchors (^, $). Practice with our online regex tester at devtoolkit.cloud/tools/regex-tester. Most regex can be built from these basics.
Is regex the same in all programming languages?
Mostly, but not exactly. JavaScript, Python, Java, and most languages support PCRE (Perl-Compatible Regular Expressions). Differences exist in lookahead/lookbehind support, Unicode handling, and flags. Always test in your target language.