You typed it out instead of copying it

The page will not open. The address looks right on screen. It was read off a phone, or off a piece of paper, or out of a photograph, and then typed into Tor Browser one character at a time.

Fifty six characters of base32 have no shape to them. Nothing in the string helps a human eye hold it. One wrong letter and the whole thing points at nothing, and the browser has no way to say so kindly.

Why the eye is no good at this

Ordinary text has redundancy. Miss a letter in a word and the word still reads. Base32 has none. Every character carries the same weight as every other, and a random string of them gives the reader no place to stumble on the error.

Three pairs cause most of the trouble. A lowercase l next to a 1 that is not even in the alphabet. A zero that cannot be there at all. A 5 mistaken for an s. Tor addresses use the letters a to z and the digits 2 to 7, which means a 0, a 1, an 8 or a 9 anywhere in a string is proof it was mangled somewhere between the source and the screen.

What the failure looks like

Tor Browser reports that the site cannot be reached, or that the onion address is invalid, depending on which part broke. If the checksum inside the address survives the typo, the client goes looking for a service that does not exist and eventually gives up. If the checksum does not survive, the client refuses before it tries anything at all.

Both messages read like a dead site to somebody who has never seen either one before. Neither one says anything about the market.

How to tell it apart from a real failure

1. Paste the address you used into a plain text editor next to the one on this page.
2. Compare the last six characters first. They are a checksum plus a version byte, so a mangled address usually differs there.
3. Compare the first six. Those carry the human readable prefix the operator paid to generate.
4. If both ends agree, compare the middle in blocks of eight rather than reading straight through.

If any character differs, the case is closed and it was this one. If none differ, the address that reached the browser is the published one, and the cause is somewhere else. The lookup step is the usual next suspect.

What follows from getting it right

Two things change. The first is that you stop hunting for a replacement address, which is the exact moment people go looking in unsafe places and end up on a page that found them on purpose. The second is that you stop treating the site as unstable, which quietly changes every judgement you make about it afterwards.

The practical rule is dull. Never type one of these. Copy it as a whole string, paste it, and check the ends after pasting, because a copy that clipped a character at either edge is the one failure mode this method still has.

• Back to the cases you caused
• What a failed page load can actually tell you
• Every case in one table

Asked often enough to answer

Is a shorter address ever valid?

No. A current onion address is fifty six characters before the suffix. Anything shorter is either an old format that no longer resolves or a string that lost characters on the way to you.

Does capitalisation matter when I copy?

No. The address is case insensitive, so a pasted address in capitals resolves the same. Character identity is what matters, not case.