Compress IPv6 addresses to short notation and expand abbreviated IPv6 addresses to full 128-bit format.
This converter changes the textual spelling of an IPv6 address without changing its 128-bit value. In expanded form, the address has eight four-digit hexadecimal hextets. In compressed form, leading zeroes disappear and one run of zero hextets can become `::`. The detail most often misread is that shorter text is not a smaller address, a subnet, or a range. Compression produces an equivalent notation; expansion reconstructs every omitted zero so the full eight-hextet layout is visible.
A concrete input and expected output from the current implementation.
Input
2001:0002:0000:0000:0000:0000:0000:0005
Expected output
2001:2::5
The input has eight hextets. Removing leading zeroes changes `0002` to `2` and `0005` to `5`; the five consecutive `0000` hextets between them are replaced by one `::`, preserving the same 128-bit value.
Each colon-delimited hexadecimal hextet represents 16 bits. When `::` appears, expansion inserts enough `0000` hextets at that position to produce eight hextets in total. Every remaining hextet is left-padded to four digits. Without `::`, an address written entirely as hexadecimal hextets must already contain eight groups, although each group may initially contain one to four digits.
Compression removes leading zeroes from each hextet. It may then replace a consecutive run of all-zero hextets with `::`; only one such replacement is possible in an address. RFC 5952 canonical form selects the longest eligible run, selects the first when equal-length runs tie, and does not use `::` for one zero hextet alone.
No. Leading zeroes inside a hextet do not affect its 16-bit value, and the number of zero hextets represented by `::` is recovered by filling the address to eight hextets. Conversion is reversible for the numeric address. It does not preserve cosmetic choices such as uppercase letters or the original placement of optional zero suppression.
No. IPv6 permits multiple equivalent textual spellings, while RFC 5952 recommends a canonical choice: lowercase hexadecimal, no unnecessary leading zeroes, and `::` for the longest eligible zero run, using the first run when lengths tie. Software that does not canonicalize may display another valid spelling. Expand both addresses and compare all eight hextets when equality is in doubt.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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