How the pattern works
| Part | Meaning |
|---|---|
25[0-5] | 250–255 |
2[0-4]\d | 200–249 |
1\d\d | 100–199 |
[1-9]?\d | 0–99, without a leading zero |
(?:…\.){3} | Three numbers, each followed by a dot |
(?:…)$ | The fourth number, then the end of the string |
Code examples
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)$/;
re.test(value); // true or falsePython
import re
bool(re.fullmatch(r'(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)', value))PHP
preg_match('/^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)$/', $value) === 1;Notes and limitations
Each octet is checked to be 0–255, which a simple \d{1,3} pattern can’t do. Leading zeros are rejected because some systems read them as octal. To accept CIDR notation, append (?:\/(?:3[0-2]|[12]?\d))? before the $.
Regex TesterType a pattern and watch matches highlight live in your test text.
Open the tool Frequently asked questions
What is the regex for IPv4 address?
/^(?:(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d\d|[1-9]?\d)$/ — it matches the whole string. See the table above for what each part does.
Which examples match?
Of the examples tested, these match: 192.168.1.1, 8.8.8.8, 255.255.255.255, 0.0.0.0. The others don’t.
How do I test this regex?
Click “Open in Regex Tester” — the pattern, flags and sample text load automatically, and matches highlight as you edit.