DevKits
29 patterns

Regex Cookbook

Battle-tested regular expressions for the tasks developers do every week — validation, extraction, cleanup — with ready-to-paste snippets in JavaScript, Python, Go, and Java.

Every entry explains the pattern piece by piece, shows real matches and non-matches, and calls out the common pitfall that catches most people — the reason your pattern “works but misses one case.” When regex is not the right tool at all (URL parsing, phone numbers, HTML), we say so and point at the language-native alternative.

Try any pattern live in our Regex Tester.

Validation

Verify that input matches an expected format — email, URL, IP, UUID, password strength.

Match an email address

[\w.+-]+@[\w-]+\.[\w.-]+

Match a URL

https?:\/\/[\w.-]+(?:\.[\w.-]+)+[\w\-._~:/?#\[\]@!$&'()*+,;=]*

Match an IPv4 address

(?:(?:25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)

Match an IPv6 address

(?:[A-Fa-f0-9]{1,4}:){7}[A-Fa-f0-9]{1,4}|::1|::

Match a UUID (v4)

[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}

Match a US phone number

(?:\+?1[-. ]?)?\(?[2-9][0-9]{2}\)?[-. ]?[2-9][0-9]{2}[-. ]?[0-9]{4}

Match a US ZIP code

\b[0-9]{5}(?:-[0-9]{4})?\b

Match a MAC address

(?:[0-9A-Fa-f]{2}[:-]){5}[0-9A-Fa-f]{2}

Match a CSS hex color

#(?:[0-9a-f]{8}|[0-9a-f]{6}|[0-9a-f]{3})\b

Validate a strong password

^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[^A-Za-z0-9]).{8,}$

Extraction

Pull specific pieces of information out of a larger text: hashtags, mentions, query params.

Match a hashtag

#\w+

Match an @-mention

@[A-Za-z0-9_]{1,39}

Extract a URL query parameter

[?&]KEY=([^&#]*)

Match a quoted string

"(?:[^"\\]|\\.)*"

Match an HTML tag

<\/?[A-Za-z][A-Za-z0-9]*\b[^>]*>

Text

Normalize and clean text: collapse whitespace, remove empty lines, catch duplicate words.

Collapse runs of whitespace

\s+

Remove empty lines

^\s*$\r?\n

Match duplicate consecutive words

\b(\w+)\s+\1\b

Dates & Times

Match ISO 8601 dates, timestamps, and 24-hour times.

Match an ISO 8601 date

\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])

Match an ISO 8601 date-time

\d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])T(?:[01]\d|2[0-3]):[0-5]\d:[0-5]\d(?:\.\d+)?(?:Z|[+-](?:[01]\d|2[0-3]):[0-5]\d)?

Match a 24-hour time

(?:[01]\d|2[0-3]):[0-5]\d(?::[0-5]\d)?

Numbers

Integers, floats, scientific notation, and hexadecimal literals.

Match an integer

-?\d+

Match a floating-point number

-?\d+(?:\.\d+)?(?:[eE][+-]?\d+)?

Match a hexadecimal number

0[xX][0-9A-Fa-f]+\b

Web

Domain names and other web-specific tokens.

Match a domain name

(?:[a-z0-9](?:[a-z0-9-]{0,61}[a-z0-9])?\.)+[a-z]{2,63}

Code

Match programming identifiers (camelCase, PascalCase, snake_case) and comments.

Match a camelCase identifier

\b[a-z]+(?:[A-Z][a-z0-9]*)+\b

Match a PascalCase identifier

\b[A-Z][a-z0-9]+(?:[A-Z][a-z0-9]+)+\b

Match a snake_case identifier

\b[a-z][a-z0-9]*(?:_[a-z0-9]+)+\b

Match a C-style comment

\/\/[^\n]*|\/\*[\s\S]*?\*\/