IPv4 Address Regex

Validation

Regular expression

/^(?:(?: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)$/

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

192.168.1.1

Should not match

256.1.1.1
not matching sample
192.168.1.1 invalid
256.1.1.1192.168.1.1

Test cases

Input	Expected	Why it matters
`192.168.1.1`	Match	Representative valid input for this pattern.
`256.1.1.1`	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.
`192.168.1.1 invalid`	No match	Common invalid or boundary input.
`256.1.1.1192.168.1.1`	No match	Common invalid or boundary input.

JavaScript

const re = /^(?:(?: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)$/;
re.test(input);

Python

import re
bool(re.search(r"^(?:(?: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)$", text))

PHP

$ok = preg_match('/^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)$/', $value) === 1;

Java

Pattern pattern = Pattern.compile("^(?:(?: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)$");
pattern.matcher(value).find();

Go

re := regexp.MustCompile(`^(?:(?: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)$`)
ok := re.MatchString(value)

Notes and production use

IPv4 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.

IPv4 Address