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IDN domains: Punycode to Unicode and back.
The domain name system only understands Latin letters, digits and hyphens. For a domain in another script to exist at all it is rewritten in Latin by a fixed rule — that rule is Punycode.
The xn-- prefix marks an encoded name. You will meet it in certificates, mail settings and server logs, where the domain almost always appears in this form.
A Cyrillic “а” and a Latin “a” look identical yet are different characters to the network. Scam domains are built on exactly this.
The domain uses ordinary Latin letters and needs no Punycode encoding at all.
One letter is swapped for a Cyrillic one. Visually identical, but it is a different domain — and it starts with xn--.
That is what makes this check useful: if a domain that looks plainly Latin converts to xn--, it contains non-Latin characters. For a banking or payment link, that is reason enough not to click.
Domains with Cyrillic and other national characters (IDN) are actually stored in DNS encoded with the xn-- prefix. This converter transforms domains both ways: пример.com → xn--...com and back. Encoding is needed when configuring DNS, SSL certificates, mail servers — anywhere a system does not understand non-Latin characters.
Another important use is security: scammers register domains visually identical to famous ones, swapping Latin letters for Cyrillic look-alikes (e.g. "а" or "о"). Run a suspicious domain through the converter and you will see its true xn-- form and instantly know if it is a fake.
