Network · Developer
IPv6 address validator.
Paste an IPv6 address to check its format, compress it to the shortest standard form, expand it to all 32 hex digits, and see what kind of address it is.
Inputs
Result
Enter an address, then press Check address.
How it's calculated
An IPv6 address is 128 bits, written as eight groups of one to four hex digits separated by colons (RFC 4291 section 2.2). One run of zero groups may be replaced by :: (used once, standing for one or more groups), and the last 32 bits may be written as a dotted IPv4 address, as in ::ffff:192.0.2.128.
Compress follows RFC 5952 section 4: drop leading zeros in each group, use lowercase, replace the longest run of zero groups with ::, choose the first run if two are the same length, and never use :: for a single zero group. Expand pads every group to four digits.
Type is matched against the IANA IPv6 address space registry and the IPv6 special-purpose address registry (RFC 6890): ::1 loopback, ::/128 unspecified, ::ffff:0:0/96 IPv4-mapped, fe80::/10 link-local, fc00::/7 unique local, ff00::/8 multicast, 2001:db8::/32 and 3fff::/20 documentation, and 2000::/3 global unicast. Registry read 2026-09-30 (IANA address space last updated 2025-10-23). Need IPv4 ranges? Use the IP range to CIDR converter.
Frequently asked questions
Why did my address change when I pressed Check?
The canonical form is the one standard way to write an address, so two people always get the same text for the same address. 2001:0db8:0000:0000:0001:0000:0000:0001 becomes 2001:db8::1:0:0:1: the first of two equal zero runs is the one that gets shortened.
Why is 2001:db8:0:1:1:1:1:1 not shortened?
RFC 5952 says :: must not replace just one zero group, so the address stays as written.
Does it accept zone IDs, ports or prefix lengths?
No. Forms like fe80::1%eth0, [::1]:80 and 2001:db8::/32 are not a bare address, so the tool asks you to remove the extra part rather than guess.
Format check only
A valid result means the text is a well-formed IPv6 address. It does not show the address is assigned, routed or reachable. Everything runs in your browser and nothing is sent anywhere.