Sixty two characters, once the suffix is attached

Where the sixty two comes from

Fifty six plus six. The suffix is a full stop followed by o n i o n, which is six characters, and it turns an encoded key into a hostname that software can route. The address alone is not a hostname. Paste fifty six characters into a browser bar without the suffix and nothing will happen.

The suffix is reserved. It is not a real top level domain and no registry sells it, which is the point. Software is expected to recognise it and hand the request to Tor rather than to the ordinary naming system, so the name never leaks to a public resolver.

What sixty two buys you

It gives you the number to check when you are looking at a full hostname rather than a bare address, which is most of the time. A line in a forum post, a line in a message, a line in a bookmark bar. Those are sixty two characters, and if one is not, something happened to it on the way.

It also gives you a way to spot a whole family of fakes quickly. A string ending in anything other than the exact six character suffix is not an onion hostname. Look for a hostname that ends in a real domain with the word onion inside it, which is how proxy sites present themselves.

That last case is worth dwelling on. Sites exist that take an onion address and serve it over the ordinary web on a normal domain. The hostname will be much longer than sixty two characters and will end in something a registry sold. Anything you send through one of those passes through a stranger in plain view.

What people get wrong about it

The most expensive mistake in this whole subject is treating a proxy hostname as a mars market working link. It loads, it looks right, and it sits between you and the market reading everything. The length check catches it immediately, because those hostnames are never sixty two characters.

A smaller error is trailing punctuation. A full stop at the end of a sentence gets copied along with the address and makes the string sixty three characters. That produces a failure, not a redirect, but it wastes time.

And people sometimes count the scheme. The characters that make up http and the slashes are not part of the hostname and should not be included in either figure.

What would move it

Only a change to the address length, since the suffix has been fixed for the entire life of onion services and reserved formally in the standards for well over a decade.

The one thing that varies in practice is what comes before the hostname and after it. A path can follow, a port can be attached. Neither belongs to the sixty two.

Questions people ask

Should I type the scheme in front?

You do not need to. Tor Browser will handle a bare hostname. The scheme is not counted in either figure on this page.

Is a .onion address a real domain name?

It is a special use name reserved in the standards so that ordinary resolvers refuse to look it up. Nobody can register or buy one.