What is the IPv6 Expander & Compressor?

Converts an IPv6 address between its fully written-out form and its shortest valid abbreviation, entirely in your browser.

How it works

An IPv6 address is 8 groups of 16 bits. To expand one, the parser splits on the '::' shorthand, fills in the missing groups with zeros, and pads each group back to 4 hex digits. To compress, it strips leading zeros from each group, finds the longest run of all-zero groups, and replaces that single longest run with '::' — skipping a run of only one zero group, since RFC 5952 says that case isn't allowed to be shortened.

SysAdmin & security use cases

Get the fully expanded form needed to write a reverse DNS (PTR) record.
Check whether two differently-formatted addresses actually refer to the same host.
Clean up an address so router or firewall configs that reject non-standard abbreviations will accept it.
Verify your own abbreviation of an address follows the RFC 5952 canonical form.