TL;DR: Free IDN ↔ punycode converter: Unicode domains to xn-- ASCII and back. Forward uses the WHATWG URL reference implementation; reverse decodes per RFC 3492. Batch, multi-line, fully local.
This tool runs entirely in your browser. Open DevTools → Network panel and search your input — it appears in no request.
Usage Guide
Internationalized domains (例子.测试) live in DNS as xn-- ASCII (punycode) while browsers display the Unicode form — two faces of one domain. This tool converts both ways: forward through the WHATWG URL IDNA implementation (identical to browser behavior), reverse per RFC 3492 label-by-label, batch multi-line. Its sharpest use case is security: phishing hides behind look-alike xn-- domains, and decoding a suspect URL settles it instantly.
1. Two directions, two implementations
- Unicode → xn--: delegated to the WHATWG URL parser (new URL) — the same IDNA implementation your browser runs, so behavior matches reality exactly; no IDNA tables to maintain.
- xn-- → Unicode: pure RFC 3492 bootstring decoding per label; one bad label never spoils the batch — failures are flagged per line.
- Batch: one domain per line; when mixing directions, check which tab you are on first.
2. The shortest anti-phishing path
Three steps for a suspicious link: forward-convert it — if pure ASCII decodes into a look-alike Unicode string (xn--pypal-4ve.com → рaypal with a Cyrillic р), it is homoglyph phishing; reverse-convert xn-- runs to expose hidden CJK domains; then diff the output against the official domain character by character (Cyrillic а ≠ Latin a — invisible to the eye, obvious in a decoded diff). Browsers show the Unicode form precisely to expose these spoofs — provided you know to decode.
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