IPv6 Address Regex

Developer

Regular expression

/(?:[0-9a-fA-F]{1,4}:){2,7}[0-9a-fA-F]{1,4}|::1/

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

2001:db8::1

Should not match

99999::1
not matching sample
2001:db8::1 invalid
99999::12001:db8::1

Test cases

Input	Expected	Why it matters
`2001:db8::1`	Match	Representative valid input for this pattern.
`99999::1`	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.
`2001:db8::1 invalid`	No match	Common invalid or boundary input.
`99999::12001:db8::1`	No match	Common invalid or boundary input.

JavaScript

const re = /(?:[0-9a-fA-F]{1,4}:){2,7}[0-9a-fA-F]{1,4}|::1/;
re.test(input);

Python

import re
bool(re.search(r"(?:[0-9a-fA-F]{1,4}:){2,7}[0-9a-fA-F]{1,4}|::1", text))

PHP

$ok = preg_match('/(?:[0-9a-fA-F]{1,4}:){2,7}[0-9a-fA-F]{1,4}|::1/', $value) === 1;

Java

Pattern pattern = Pattern.compile("(?:[0-9a-fA-F]{1,4}:){2,7}[0-9a-fA-F]{1,4}|::1");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`(?:[0-9a-fA-F]{1,4}:){2,7}[0-9a-fA-F]{1,4}|::1`)
ok := re.MatchString(value)

Notes and production use

IPv6 Address 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.

IPv6 Address