Are there any standards for mapping ICANN domains-world websites to .onion addresses?

I’m interested in any machine-readable methods that can be used to discover a .com’s .onion domain.

E.g. is there a standard method to announce that https://www.bbc.com/ is also available at https://www.bbcnewsv2vjtpsuy.onion/? Given the .com, how would I auto-discover (and ideally verify) the .onion? (This is obviously only applicable for real-world websites that offer a Tor hidden service mirror.)

The only resource I’ve found is the short manually curated list in the Real-World Onion Websites project.

I’ve dreamed up a /.well-known/mirrors.txt URI auto-discovery mechanism. That file would list all mirrors of a website. You could include your .onion address and your .com in that file. If the file is accessible from both location and contain each other than you’ve got a verified domain match between an .onion and an ICANN domain.

RFC 8164 proposes something similar for auto-discovering HTTPS-support. The Dat protocol uses something similar too.

  • 1
    I think the reason no one has responded is because it is more of a webserver question than merely a Tor question. My suggestion would be to contact Alec Muffett. You linked to his "Real-World Onion Websites project" and see if he can provide some illumination. He literally runs the onion service for Facebook.
    – elmerjfudd
    Commented Dec 13, 2019 at 20:13

2 Answers 2


The header you're looking for is Alt-Svc; the most accessible write-up I've found is Jonah Aragon's "Securing Services with Tor and alt-svc", but there are other guides and articles out there about it. It works much the same as your /.well-known/mirrors.txt idea.

  • Cloudflare uses this but the addresses it assigns to customers are short-lived/unstable.
    – Daniel
    Commented Dec 24, 2019 at 10:40

Tor has introduced a new HTTP response header for this purpose: Onion-Location.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .