What is the format of .onion pseudo-top-level domain addresses?

2 Answers 2


Quoting from Wikipedia:

Addresses in the .onion pseudo-TLD are opaque, non-mnemonic, 16-character alpha-semi-numeric hashes which are automatically generated based on a public key when a hidden service is configured. These 16-character hashes can be made up of any letter of the alphabet, and decimal digits beginning with 2 and ending with 7, thus representing an 80-bit number in base32.


Onion-addresses can also have another "subdomain" part on the beginning

so you can have


As well as


For SSL technical reasons, the clearnet tor2web proxies don't support these domain names (e.g. tor2web.org )

  • Are you sure, to my knowledge the tor spec doesn't currently allow subdomains.
    – puser
    Commented Aug 20, 2014 at 16:38

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