application/vnd.rar

WinRAR's proprietary archiver — anyone may write a decompressor from the published technote, but only RARLAB's code is licensed to create archives, which is why your language's standard library extracts .rar and never produces it. IANA registered application/vnd.rar in 2016, decades after the format shipped, so the wild still overwhelmingly sends the unregistered application/x-rar-compressed; treat the two as the same thing arriving under different names. Every archive opens with a marker spelling Rar plus a bang: version 4 follows it with a 00 byte, RAR 5.0 with 01 00.

Defined by RAR 5.0 archive format · IANA registration. Registry facts from the IANA media-types registry via mime-db.