IDN Decode - TestMu AI (Formerly LambdaTest)

What is IDN Decode?

IDN Decode, also called ToUnicode, converts Punycode (an ASCII string beginning with xn--) back into the readable Unicode domain name it represents. Punycode is defined by RFC 3492. For example, this tool decodes xn--exmple-cua.com into exämple.com. It is the inverse of the IDN Encode tool, which turns Unicode back into Punycode.

IDN Encoding vs IDN Decoding: What is the difference?

Every internationalized domain name has two forms: the Unicode form people read and the Punycode (xn--) form the DNS actually stores. Encoding and decoding move between them in opposite directions.

This page decodes. To go the other way, use the IDN Encode tool, or the Punycode Converter to move in both directions in one place.

What is an IDN homograph attack?

An IDN homograph attack registers a domain using lookalike Unicode characters (homoglyphs) from scripts such as Cyrillic or Greek to imitate a trusted brand for phishing and spoofing. The Latin "a" and the Cyrillic "а" (U+0430) look identical, so аpple.com written with a Cyrillic а is a different domain from the real apple.com.

Decoding exposes the deception. That Cyrillic lookalike is stored as xn--pple-43d.com, and decoding it here surfaces the mixed-script name so you can tell it apart from the genuine site. Security analysts and QA teams use IDN Decode to inspect suspicious links before they reach users, and validate how those links render across 10,000+ real devices.

Technical standards: IDNA2003, IDNA2008, and RFC 3492

Punycode itself is defined by RFC 3492, but the rules for which Unicode characters are allowed and how they map to Punycode come from the IDNA (Internationalizing Domain Names in Applications) standard. Two versions are in use: IDNA2003 and the newer IDNA2008 (RFC 5890 to 5894).

The versions disagree on a handful of characters. The German Eszett (ß) and the Greek final sigma (ς) are mapped to "ss" and "σ" under IDNA2003 but kept as distinct characters under IDNA2008, so the same label can decode differently depending on which rules a resolver follows. The Unicode UTS #46 mapping was created to bridge the two.

How to use the IDN Decode tool

• Enter the Punycode: paste a domain in its xn-- form, for example xn--bcher-kva.com, into the Enter Value field.
• Click IDN Decode: the domain is sent to TestMu AI's conversion API and decoded with ToUnicode.
• Read the Output: the readable Unicode name, such as bücher.com, appears in the Output field.
• Inspect the result: check for mixed scripts or unexpected characters that can signal a homograph spoof.

No signup is required. A domain that is already in Unicode, or plain ASCII with no xn-- label, is returned unchanged.

Frequently Asked Questions (FAQs)

Is IDN Decode the same as IDN Encode?

No. IDN Decode (ToUnicode) converts Punycode, the ASCII form starting with xn--, back into the readable Unicode domain name. IDN Encode (ToASCII) does the reverse, turning Unicode characters into Punycode. For example, IDN Decode turns xn--exmple-cua.com into exämple.com.

What does IDN Decode convert xn-- domains into?

It converts a Punycode label such as xn--bcher-kva.com into its original Unicode form, bücher.com. Punycode, defined by RFC 3492, is the ASCII-compatible encoding the DNS uses to represent internationalized domain names.

What is an IDN homograph attack?

An IDN homograph attack registers a domain using lookalike Unicode characters (homoglyphs) from scripts like Cyrillic or Greek to imitate a trusted brand for phishing. For example, аpple.com written with a Cyrillic а resolves to xn--pple-43d.com. Decoding a suspicious xn-- domain reveals the real characters behind it.

What is the difference between IDNA2003 and IDNA2008?

IDNA2003 and IDNA2008 are the two versions of the standard that maps Unicode domains to Punycode. They treat a few characters differently: the German Eszett (ß) and Greek final sigma (ς) are mapped to ss and σ under IDNA2003 but kept as distinct characters under IDNA2008, which can change how a name decodes.

Does the IDN Decode tool store my input?

The domain you enter is sent to TestMu AI's conversion API, decoded, and returned in the Output field. No account or signup is required to use the tool.

What is an Internationalized Domain Name (IDN)?

An Internationalized Domain Name (IDN) is a domain that contains at least one label in a non-ASCII script, such as Arabic, Chinese, or Cyrillic, or a Latin script with diacritics like é or ü. IDNs let people register and use domains in their native language.