Validating IP Addresses with Regex (and Better Ways)

Updated: 2026-05-30

Regex can match the shape of an IP, but real validation (ranges, IPv6 compression) is better left to a parser.

IPv4 Regex

Each octet must be 0–255:

^((25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)$

That already shows how fiddly it gets — and IPv6 regex (with :: compression and embedded IPv4) is far worse and error-prone.

Prefer a Parser

Most languages validate correctly in one line:

import ipaddress
def is_ip(s):
    try: ipaddress.ip_address(s); return True
    except ValueError: return False

ok := net.ParseIP(s) != nil

import net from "node:net";
const ok = net.isIP(s) !== 0; // 4, 6, or 0

See more in IP programming samples.

Use regex only for a quick format filter. For "is this a usable address, and is it in my allowed range?", use a parser plus CIDR check — try the subnet calculator to reason about ranges.