Common use cases
- ✓Network configuration forms
- ✓Log and telemetry validation
- ✓Allowlist and blocklist input checks
JavaScript-compatible regex reference
IPv4 Address Regex Pattern & Tester
Validate dotted-decimal IPv4 addresses with four octets constrained to the numeric range 0–255. This pattern is stricter than the common \d{1,3} shortcut, which also accepts impossible values such as 999.999.999.999.
Pattern
^(?:(?:25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)\.){3}(?:25[0-5]|2[0-4]\d|1\d{2}|[1-9]?\d)$Flags: none
Live test vectors
Test the IPv4 address regex
Enter one value per line. Each line is tested against the whole-string pattern using the browser JavaScript RegExp engine.
PASS
192.168.1.1PASS
10.0.0.1PASS
255.255.255.255PASS
0.0.0.0FAIL
256.1.1.1FAIL
192.168.1FAIL
999.999.999.999FAIL
01.2.3.4Quick answer
A useful IPv4 validation regex must constrain each octet to 0–255, not merely one to three digits. This version also avoids leading-zero forms such as 01 in order to keep the accepted representation unambiguous.
Pitfalls and limitations
- !\d{1,3} does not enforce the 0–255 range.
- !Anchors are required when validating the entire field rather than searching inside a larger string.
- !Some systems accept historical leading-zero forms; this pattern intentionally does not.
Known-valid examples
192.168.1.110.0.0.1255.255.255.2550.0.0.0Known-invalid examples
256.1.1.1192.168.1999.999.999.99901.2.3.4Continue testing and debugging
Frequently asked questions
Why not use \d{1,3} for each IPv4 octet?
Because it accepts values greater than 255. Range-aware alternatives are needed when the goal is validation rather than loose extraction.
Does this pattern accept leading zeros?
No. It accepts 0 but rejects forms such as 01 or 001 to avoid ambiguous textual representations.
Can this regex validate whether an IP is publicly routable?
No. It checks IPv4 syntax and numeric octet ranges only. Private, loopback, multicast, documentation, and other reserved ranges require separate semantic checks.