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Umlauts, IDNs and Punycode

Why a name such as büro.ch also has a technical form beginning with xn--.

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Two forms of one domain

An internationalised domain name (IDN) can contain supported non-ASCII characters such as an umlaut. People usually see the Unicode form, while DNS stores an ASCII-compatible form called Punycode. A Punycode label begins with xn--.

These are not two separately registered domains. olu normalises the name and shows the readable and technical forms where that helps prevent ambiguity.

Using an IDN safely

  1. Copy the readable spelling carefully and check every character before purchase or transfer.
  2. When a third-party DNS or hosting form rejects the Unicode spelling, use the Punycode form olu displays.
  3. Test browsers, links and email clients. Not every mail system supports internationalised addresses even when the domain itself works.
  4. Consider registering an ASCII alternative when mishearing or keyboard availability would cause confusion.

Frequently asked questions

Is an xn-- name suspicious?

Not by itself; it is the normal DNS encoding for an IDN. Still inspect the decoded spelling because lookalike Unicode characters can be abused.