Blossom checker

How Blossom names files

Blossom is Nostr's convention for media hosting, and its core idea is content addressing: a file is identified by the sha256 hash of its bytes, not by a path a server made up. The same picture has the same hash on every server that stores it, so a url like server.example/abc123 is really two claims: this server has the file, and the file's bytes hash to abc123.

That design is what makes media portable. If one server disappears, any other server holding the same bytes serves the same content at the same name, and clients can fall back without links rotting.

What this checker does

Given a hash, the tool queries a set of well known Blossom servers, including Azzamo's, asking each whether it has the blob. You see at a glance where a file lives and where it does not, which is exactly the redundancy question that decides whether your media survives a server outage.

The verify step goes further: it downloads the file from a server that claims to have it, hashes the bytes in your browser with the Web Crypto API, and compares the result to the hash in the name. A match proves the server returned exactly the content the name promises, unmodified. A mismatch means the server is buggy or lying, and either way you should not trust that copy.

Why redundancy is the whole game

A note lives on many relays, but media is heavier and most people upload a picture to exactly one host. When that host prunes old files or shuts down, every note embedding that picture breaks at once. The fix is boring and effective: keep your files on more than one server, and check occasionally that they are still where you think.

If a file you care about shows up on only one server in the results, that is your cue to mirror it somewhere else before you need it.

Content addressing also means the checker never needs to trust a server list from anyone: any Blossom server can be asked the same question about the same hash. If you run your own server, add it mentally to the results here; the point is not this specific list, but that the same file is verifiable wherever it lives.