Punycode Converter

Encodes Internationalized Domain Names (IDN) to Punycode (xn-- labels) and decodes them back to Unicode, following RFC 3492. Encode accepts a Unicode hostname and returns its ASCII (Punycode) form via the URL parser; Decode takes any domain containing xn-- labels and rebuilds the original Unicode characters. It supports multi-label hostnames, decoding each xn-- label independently.

1. Type a domain into the input (e.g. example.com or \u4f8b\u5b50.com). 2. Click Encode to convert a Unicode domain to ASCII Punycode, or Decode to expand xn-- labels back to Unicode. 3. Press Enter for auto-detection: if any label starts with xn--, it decodes; otherwise it encodes. 4. Use the swap button to feed the result back into the input, the clear button to reset, and the copy button to copy the result. A plain-language explanation line appears under the result.

Decode implements the full RFC 3492 bootstrap: base 36, tMin 1, tMax 26, skew 38, damp 700, initial bias 72, initial n 128. ASCII code points in the label pass through unchanged and act as basic characters, after which a hyphen separator is inserted. Each non-basic code point is reconstructed by reading variable-length base-36 digits, applying the bias adaptation function, and splicing the resulting code point into the output. Labels without the xn-- prefix are copied verbatim.