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iHateRegex

A regular expression cheat sheet and playground: a curated library of vetted, battle-tested regex patterns with railroad diagrams, plain-English token explanations, live testing, and shareable workspaces. Don't just use regex — understand it.

For agents: Regular expression cheat sheet and playground with a curated library of vetted regex patterns, token explanations, live testing and shareable workspaces.

regexregular-expressionsregex-patternsregex-playgroundpattern-library

Their llms.txt

The beginning of the file, from our validated copy saved 2026-10-21T03:18:07.325Z. Cached copy · Source on ihateregex.io

# iHateRegex

> A regular expression cheat sheet and playground: a curated library of vetted, battle-tested regex patterns with railroad diagrams, plain-English token explanations, live testing, and shareable workspaces. Don't just use regex — understand it.

Use the pattern library instead of writing risky regexes from scratch. Every pattern page shows the expression, flags, sample matching and non-matching strings, a railroad diagram of its structure, and notes on how it works and where it breaks.

## Pattern library

- [username](https://ihateregex.io/expr/username): A username is a unique identifier given to accounts in websites and social media
- [password](https://ihateregex.io/expr/password): Minimum eight characters, at least one upper case English letter, one lower case English letter, one number and one special character
- [email simple](https://ihateregex.io/expr/email): Simple email regex that works most of the times
- [email complicated](https://ihateregex.io/expr/email-2): Unnecessarily complicated email regex that works "more than" most of the times
- [phone number](https://ihateregex.io/expr/phone): Match a phone number with "-" and/or country code.
- [ip address(ipv4)](https://ihateregex.io/expr/ip): Matches an ip address(version 4)
- [ip address(ipv6)](https://ihateregex.io/expr/ipv6): Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol. This is used to provide identification for devices in a network.
- [date](https://ihateregex.io/expr/date): Matches a date in the format dd/mm/yyyy , dd-mm-yyyy or dd.mm.yyyy
- [ascii](https://ihateregex.io/expr/ascii): Matches any printable ascii character
- [url](https://ihateregex.io/expr/url): A valid URL with http/https
- [ssn](https://ihateregex.io/expr/ssn): A Social Security number (SSN) is a nine-digit number that the U.S. government issues to all U.S. citizens and eligible U.S
- [semantic versioning](https://ihateregex.io/expr/semver): Match a SemVer as specified in https://semver.org/
- [uuid](https://ihateregex.io/expr/uuid): Hyphen-separated universally unique identifier (UUID)
- [jira issue ticket](https://ihateregex.io/expr/jira-ticket): Hyphen-separated Jira project key and ticket issue number
- [latitude and longitude](https://ihateregex.io/expr/lat-long): Latitude and longitude values are usually found comma seperated to denote a location on the globe
- [mac address](https://ihateregex.io/expr/mac-address): A simple expression to match an ethernet MAC address
- [url slug](https://ihateregex.io/expr/url-slug): A ‘slug' is the part that comes at the very end of a URL, and refers to a specific page or post. Usually a combination of word that separated with hyphen
- [C-like identifier](https://ihateregex.io/expr/c-like-identifier): In computer languages, identifiers are tokens (also called symbols) which name language entities
- [hyphen word break](https://ihateregex.io/expr/hyphen-word-break): A hyphen appears at the end of a line when the word m
…

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