Domain Punycode Converter rfc 3492

What this tool does

The domain name system was designed to handle only letters, digits, and hyphens. As addresses written in other scripts became necessary, a standard way to represent Unicode characters using the permitted character set was introduced. That mechanism is Punycode, and it underpins internationalised domain names.

Converted labels begin with xn--. A Korean domain such as 한글도메인.kr becomes xn--bj0bj3i97fq8o5lq.kr. Browsers display the native form in the address bar, but DNS lookups, certificate issuance, and server configuration all use the xn-- form.

Anyone operating an internationalised domain therefore needs both forms. Certificate signing requests, web server and mail server configuration, and domain fields in third-party services usually require the Punycode form to work correctly.

When to use it

Use it when requesting an SSL certificate for an internationalised domain, when registering the domain in DNS or web server configuration, when investigating why a link containing non-ASCII characters breaks, or when checking what an unfamiliar xn-- address in an email really is.

Input and output examples

Notes and limitations

Homograph attacks use characters that look identical to Latin letters, such as Cyrillic a, to imitate well-known sites. Browsers mitigate this by displaying the raw xn-- form under certain conditions. Checking an unexpected link with this tool is a sensible precaution. Internationalised domains are also unsupported in some email systems and older software.

Frequently asked questions