Regex for IPv6 Addresses

Read it left to right. Each piece below matches one part of the input:

• (?:[0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4} Eight full hextets: 1:2:3:4:5:6:7:8.
• (?:[0-9A-Fa-f]{1,4}:){1,7}: One to seven hextets then :: at the end, like fe80::.
• (?:[0-9A-Fa-f]{1,4}:){1,6}:[0-9A-Fa-f]{1,4} :: before the last hextet, like 2001:db8::1.
• (?:…){1,5}(?::…){1,2} … (?:…){1,2}(?::…){1,5} The :: in every middle position, with at most seven hextets in total.
• [0-9A-Fa-f]{1,4}:(?::[0-9A-Fa-f]{1,4}){1,6} One hextet, then :: and up to six more.
• :(?:(?::[0-9A-Fa-f]{1,4}){1,7}|:) :: at the very start, like ::1, or the unspecified address :: itself.

The whole input must match, from the first character to the last. Every row below is checked against the pattern by our automated test suite before each release.

Two legal forms are deliberately not covered, to keep the pattern readable:

• Embedded IPv4, such as ::ffff:192.0.2.1 (IPv4-mapped) and 64:ff9b::192.0.2.1 (NAT64). These end in a dotted quad.
• Zone IDs, such as fe80::1%eth0, which name the network interface for link-local addresses.

If your input can contain them, use a parser instead of growing the regex further: net.isIPv6() in Node.js, ipaddress.IPv6Address in Python, netip.ParseAddr in Go, IPAddress.TryParse in .NET or filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6) in PHP. They also handle the address types (RFC 4291) for you.

The same address has many spellings: 2001:DB8:0:0:0:0:0:1, 2001:db8::1 and 2001:0db8::0001 are identical. Comparing strings will report them as different. Normalize to the canonical form from RFC 5952 before storing or comparing: lowercase, no leading zeros, and :: replacing the longest run of zero groups. Python's str(ipaddress.ip_address(s)) and Go's netip.Addr.String() both produce it.

The pattern is translated for each engine rather than pasted as is: named groups, anchors, escapes, shorthand classes and flags are adjusted so each snippet behaves as closely to the JavaScript version as its engine allows. Differences that remain (Go's RE2 has no lookarounds or backreferences, for example) are called out under each one. The Code tab in the tester above also exports Dart, and updates as you edit the pattern.

JavaScript and TypeScript

const regex = /^(?:(?:[0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,7}:|(?:[0-9A-Fa-f]{1,4}:){1,6}:[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,5}(?::[0-9A-Fa-f]{1,4}){1,2}|(?:[0-9A-Fa-f]{1,4}:){1,4}(?::[0-9A-Fa-f]{1,4}){1,3}|(?:[0-9A-Fa-f]{1,4}:){1,3}(?::[0-9A-Fa-f]{1,4}){1,4}|(?:[0-9A-Fa-f]{1,4}:){1,2}(?::[0-9A-Fa-f]{1,4}){1,5}|[0-9A-Fa-f]{1,4}:(?::[0-9A-Fa-f]{1,4}){1,6}|:(?:(?::[0-9A-Fa-f]{1,4}){1,7}|:))$/;

function isValid(value) {
  return regex.test(value);
}

console.log(isValid("2001:0db8:85a3:0000:0000:8a2e:0370:7334"));

Python

import re

pattern = re.compile(r"^(?:(?:[0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,7}:|(?:[0-9A-Fa-f]{1,4}:){1,6}:[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,5}(?::[0-9A-Fa-f]{1,4}){1,2}|(?:[0-9A-Fa-f]{1,4}:){1,4}(?::[0-9A-Fa-f]{1,4}){1,3}|(?:[0-9A-Fa-f]{1,4}:){1,3}(?::[0-9A-Fa-f]{1,4}){1,4}|(?:[0-9A-Fa-f]{1,4}:){1,2}(?::[0-9A-Fa-f]{1,4}){1,5}|[0-9A-Fa-f]{1,4}:(?::[0-9A-Fa-f]{1,4}){1,6}|:(?:(?::[0-9A-Fa-f]{1,4}){1,7}|:))\Z")

def is_valid(value: str) -> bool:
    return pattern.search(value) is not None

print(is_valid("2001:0db8:85a3:0000:0000:8a2e:0370:7334"))

• JavaScript's $ only matches at the very end of the string. Python's $ also matches before a trailing newline, so the pattern uses \Z instead.

Go

package main

import (
	"fmt"
	"regexp"
)

func main() {
	re := regexp.MustCompile(`^(?:(?:[0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,7}:|(?:[0-9A-Fa-f]{1,4}:){1,6}:[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,5}(?::[0-9A-Fa-f]{1,4}){1,2}|(?:[0-9A-Fa-f]{1,4}:){1,4}(?::[0-9A-Fa-f]{1,4}){1,3}|(?:[0-9A-Fa-f]{1,4}:){1,3}(?::[0-9A-Fa-f]{1,4}){1,4}|(?:[0-9A-Fa-f]{1,4}:){1,2}(?::[0-9A-Fa-f]{1,4}){1,5}|[0-9A-Fa-f]{1,4}:(?::[0-9A-Fa-f]{1,4}){1,6}|:(?:(?::[0-9A-Fa-f]{1,4}){1,7}|:))$`)
	fmt.Println(re.MatchString("2001:0db8:85a3:0000:0000:8a2e:0370:7334"))
}

C#

using System;
using System.Text.RegularExpressions;

// The timeout stops a pathological input from hanging the thread (ReDoS).
var regex = new Regex(@"^(?:(?:[0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,7}:|(?:[0-9A-Fa-f]{1,4}:){1,6}:[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,5}(?::[0-9A-Fa-f]{1,4}){1,2}|(?:[0-9A-Fa-f]{1,4}:){1,4}(?::[0-9A-Fa-f]{1,4}){1,3}|(?:[0-9A-Fa-f]{1,4}:){1,3}(?::[0-9A-Fa-f]{1,4}){1,4}|(?:[0-9A-Fa-f]{1,4}:){1,2}(?::[0-9A-Fa-f]{1,4}){1,5}|[0-9A-Fa-f]{1,4}:(?::[0-9A-Fa-f]{1,4}){1,6}|:(?:(?::[0-9A-Fa-f]{1,4}){1,7}|:))\z", RegexOptions.None, TimeSpan.FromSeconds(1));
Console.WriteLine(regex.IsMatch("2001:0db8:85a3:0000:0000:8a2e:0370:7334"));

• JavaScript's $ only matches at the very end of the string. .NET's $ also matches before a trailing newline, so the pattern uses \z instead.

PHP

<?php

$pattern = '/^(?:(?:[0-9A-Fa-f]{1,4}:){7}[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,7}:|(?:[0-9A-Fa-f]{1,4}:){1,6}:[0-9A-Fa-f]{1,4}|(?:[0-9A-Fa-f]{1,4}:){1,5}(?::[0-9A-Fa-f]{1,4}){1,2}|(?:[0-9A-Fa-f]{1,4}:){1,4}(?::[0-9A-Fa-f]{1,4}){1,3}|(?:[0-9A-Fa-f]{1,4}:){1,3}(?::[0-9A-Fa-f]{1,4}){1,4}|(?:[0-9A-Fa-f]{1,4}:){1,2}(?::[0-9A-Fa-f]{1,4}){1,5}|[0-9A-Fa-f]{1,4}:(?::[0-9A-Fa-f]{1,4}){1,6}|:(?:(?::[0-9A-Fa-f]{1,4}){1,7}|:))$/D';

function isValid(string $value, string $pattern): bool
{
    return preg_match($pattern, $value) === 1;
}

var_dump(isValid('2001:0db8:85a3:0000:0000:8a2e:0370:7334', $pattern));

• The D modifier makes $ match only at the very end, like JavaScript (PCRE's $ also matches before a trailing newline).

• Regex for IPv4 Addresses: Four octets from 0 to 255, no leading zeros, nothing before or after.
• Regex for MAC Addresses: Six hex pairs with consistent : or - separators, or Cisco's dotted form.
• Regex for Domain Names: Hostnames with valid labels, a 253-character limit and Punycode support.
• Regex for URL Validation: http and https links with a real domain, optional port, path, query and fragment.

Browse all 25 patterns in the regex pattern library, or build your own in the regex tester.