Punycode / IDN
How domains speak Arabic and Cyrillic.
Where it came from
The Domain Name System only speaks ASCII, but the world does not. IDN (Internationalized Domain Names) solved this in the early 2000s with Punycode (RFC 3492), translating Unicode labels into ASCII that DNS accepts.
So "россия.рф" becomes "xn--h1alffa9f.xn--p1ai". The "xn--" prefix marks a Punycode label — and it is also why lookalike "homograph" phishing (cyrillic а vs latin a) is a real threat.
How it works
Punycode isolates the non-ASCII part and encodes it as a base-36-ish sequence after a "-" delimiter, with the ASCII prefix kept verbatim. Decoding reverses it.
UWC converts between human-readable IDN and its ASCII Punycode form in your browser — handy for verifying what a suspicious domain actually is.
Use IDN / Punycode
Decode xn-- domains to see the real characters — or encode them, locally.