Domain Name Regex

Extraction

Regular expression

/(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}/

Pattern breakdown

Part	Meaning
`Anchor or context`	Use anchors when you need whole-string validation.
`Main token`	The core token sequence describes the accepted text shape.
`Character class`	Character classes limit which characters are valid.
`Quantifier`	Quantifiers control how many characters or groups are accepted.
`Flags`	Use language-specific flags such as i, m, or u only when needed.

Should match

cdn.example.co
cdn.demo.co

Should not match

localhost
not matching sample
cdn.example.co invalid
localhostcdn.example.co

Test cases

Input	Expected	Why it matters
`cdn.example.co`	Match	Representative valid input for this pattern.
`cdn.demo.co`	Match	Representative valid input for this pattern.
`localhost`	No match	Common invalid or boundary input.
`(empty string)`	No match	Common invalid or boundary input.
`not matching sample`	No match	Common invalid or boundary input.
`cdn.example.co invalid`	No match	Common invalid or boundary input.
`localhostcdn.example.co`	No match	Common invalid or boundary input.

JavaScript

const re = /(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}/;
re.test(input);

Python

import re
bool(re.search(r"(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}", text))

PHP

$ok = preg_match('/(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}/', $value) === 1;

Java

Pattern pattern = Pattern.compile("(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,}");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}`)
ok := re.MatchString(value)

Notes and production use

Domain Name regex is useful as a practical starting point. Test it against your real input, avoid using it as the only security control, and prefer a parser when the format has complex grammar.

Performance tip: avoid running complex regular expressions repeatedly on very large untrusted strings without limits. Prefer anchored validation patterns, cap input length before matching, and use a parser when the target format has nested grammar.

Domain Name