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Working with international domain names and seeing xn-- prefixes?

Punycode converts Unicode domains to ASCII. Convert between them here.

Punycode Converter

Convert international domain names (IDN) to Punycode (ASCII) and back

Internationalized Domain Names and Punycode

The Punycode Converter translates internationalized domain names (IDNs) between Unicode and ASCII-compatible Punycode encoding. This is essential for web developers working with multilingual domains, DNS administrators, and anyone who needs to understand how non-Latin characters are represented in the DNS system.

How Browsers Handle Non-Latin Domains

When you type a domain like münchen.de in your browser, it automatically converts each label with non-ASCII characters into Punycode (e.g., xn--mnchen-3ya.de) before performing the DNS lookup. The xn-- prefix is the ACE (ASCII Compatible Encoding) marker defined by IDNA that signals a Punycode-encoded label.

Common Mistakes

  • ✗Confusing Punycode with URL encoding — Punycode is for DNS labels only, not URL paths or query strings
  • ✗Manually registering domains with the xn-- prefix — most registrars handle the Unicode-to-Punycode conversion automatically
  • ✗Ignoring homograph attack risks when registering or visiting internationalized domains with mixed scripts

Pro Tips

  • ✓Use this tool to verify what a Unicode domain looks like in Punycode before purchasing from a registrar
  • ✓Modern browsers display the Unicode form in the address bar but use Punycode internally for DNS resolution
  • ✓If you see xn-- in a domain name, that label contains non-ASCII characters — use this tool to decode it

Real-World Examples

Chinese domain

中文.com becomes xn--fiqs8s.com — the xn-- prefix marks it as a Punycode-encoded label

German domain with umlauts

münchen.de becomes xn--mnchen-3ya.de — ü is encoded into the ACE suffix

Cyrillic domain

россия.рф becomes xn--h1alffa9f.xn--p1ai — both the domain and TLD are encoded

Examples:

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About Punycode & Internationalized Domain Names

What is Punycode?

Punycode is an encoding syntax defined in RFC 3492 that represents Unicode strings using only ASCII characters. It is a core component of Internationalized Domain Names in Applications (IDNA), allowing domain names to include characters from non-Latin scripts such as Chinese, Arabic, Cyrillic, Hebrew, and many others.

When a domain like 中文.com is encoded in Punycode, it becomes xn--fiqs8s.com. The xn-- prefix signals that the label is an ASCII Compatible Encoding (ACE) of a Unicode string.

Why Punycode Exists

The DNS (Domain Name System) was originally designed to work only with ASCII characters (letters a-z, digits 0-9, and hyphens). This worked fine for English-speaking users but excluded billions of people whose languages use other scripts. Punycode bridges this gap by encoding any Unicode string into a safe ASCII format that DNS servers can handle.

Punycode uses a variable-length encoding scheme called Bootstring. Basic ASCII characters pass through unchanged, while non-ASCII characters are encoded as a series of suffix digits appended after a - delimiter. The algorithm is remarkably compact -- it can represent any Unicode string using only the 36 characters a-z and 0-9.

How Domain Names Work with Unicode

When you type a domain like münchen.de in your browser, the following happens behind the scenes:

1. User input: You type or paste the Unicode domain name in the address bar.

2. IDNA processing: The browser converts each label (the parts between dots) from Unicode to Punycode. Purely ASCII labels pass through unchanged; labels with non-ASCII characters become xn-- prefixed ACE strings.

3. DNS lookup: The browser sends the fully-ASCII domain to DNS servers. For münchen.de, it queries xn--mnchen-3ya.de.

4. Display: The browser receives the response and displays the original Unicode domain in the address bar for readability.

This utility is provided for informational purposes only. KnowKit is not responsible for any errors in the output.

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Frequently Asked Questions

What does the "xn--" prefix mean?

It is the ACE (ASCII Compatible Encoding) prefix defined in IDNA. It tells DNS and software that the label is a Punycode-encoded string. Only labels containing non-ASCII characters get this prefix.

Is Punycode the same as URL encoding?

No. URL encoding (percent-encoding) represents characters as %XX hex sequences and is used in URL paths and query strings. Punycode is specifically for DNS labels and uses a more efficient algorithm that handles the entire Unicode range.

Can I register a Punycode domain?

Yes. Domain registrars accept both Unicode and Punycode forms. Most modern registrars handle the conversion automatically, so you can register 中文.com without manually converting it.

Are Punycode domains safe?

Punycode is safe by design, but it can be exploited in homograph attacks where visually similar characters from different scripts are used to create phishing domains. For example, the Cyrillic "а" looks identical to the Latin "a". Modern browsers display Punycode domains when they detect potential homograph attacks to protect users.