/blog/ · field notes from the hunt
/^(?=.*[a-z])(?=.*[A-Z])(?=.*\d).{8,}$/
Secret123aB3defghTr0ub4dor9Lives_cat·secret123SECRET123SecretpassAb1
How to check \"at least one uppercase letter, one digit, eight characters\" in a single regex with lookaheads, why the order-free version needs them, the traps in the common patterns, and why checking each rule separately is often the better design.
Regex Hunter/^(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)$/
042199255·256300071000
An IPv4 address is four numbers from 0 to 255. Here's why the obvious \d{1,3} pattern lets 999.999.999.999 through, how to match one octet with alternation, what to do about leading zeros, and how to find addresses inside text.
Regex Hunter/^https?://\S+$/
https://a.iohttp://x.com/phttps://b.dev?q=1·ftp://x.comwww.x.comhttp:/x.com
Finding links in text and validating a URL are different jobs. Here's a pattern for each, the traps that let bad URLs through (trailing punctuation, unescaped dots, missing anchors), and when to hand the work to new URL() or urllib.
Regex Hunter/^\d{3}[-. ]?\d{3}[-. ]?\d{4}$/
555-123-4567555.123.45675551234567·555-123455-123-4567555-123-456
People type the same phone number a dozen ways. Here's how to match US numbers with dashes, dots, spaces, parentheses and an optional +1, how to check the international E.164 format, and why real validation needs a library.
Regex Hunter/^[^\s@]+@[^\s@]+\.[^\s@]+$/
ana@site.comx+t@site.iojo@mail.co.uk·ana@example@site.coma@@b.io
Three copy-ready email regex patterns (simple, practical and strict), when to use each, and the common mistakes that reject real addresses.
Regex HunterToday’s board is live
Match every monster, spare every innocent — in as few characters as you can.