Credits and licences

Last updated 2026-10-13

Our own code

The tools and page layouts are written for this site; no third-party code library is used. Pages only contact this site’s own read-only check service, and only when you press a check button (see the privacy policy).

Third-party material

No third-party code. The hreflang generator’s language and region code lists come from public reference lists: ISO 639-1 two-letter language codes as published by the Library of Congress (ISO 639-2 registration authority) and ISO 3166-1 alpha-2 region codes as listed in the UN Statistics Division’s M49 table plus TW, which ISO 3166-1 assigns but the M49 table does not list (downloaded on 13 October 2026). Rules on the tool pages are taken from the public documentation linked in each page’s Sources line (RFC 9309, the sitemaps.org protocol, schema.org, the Open Graph protocol, IETF RFCs and Google Search Central).