Blossom Protocol Reference: The BUD Registry (Nostr Blob Storage)

Quick answer

Blossom is a Nostr-native protocol for storing binary blobs (images, files, media) on public HTTP servers, addressed by their SHA-256 hash and authenticated with your Nostr keys — so your media is content-addressed and portable across servers instead of locked to one host. Its features are defined in numbered specs called BUDs (Blossom Upgrade Documents), BUD-00 through BUD-12. The registry below is sourced from the Blossom repository (public domain).

Sourced from github.com/hzrd149/blossom (Unlicense / public domain), as of 2026-07-21. Blossom is young and evolving — confirm the current wording of any BUD at the repo before you build against it.

BUD	Title	What it defines
`BUD-00`	Blossom Upgrade Documents	The meta-spec: how BUDs are numbered and how servers advertise the additional features they implement.
`BUD-01`	Server requirements & blob retrieval	The core: fetch a blob by its SHA-256 hash over HTTP (GET /<sha256>), and the baseline server behaviour.
`BUD-02`	Blob upload & management	The upload mechanism (PUT /upload) and the blob descriptor a server returns for a stored blob.
`BUD-03`	User Server List	How a user publishes the list of Blossom servers they prefer, so clients know where to store and find their blobs.
`BUD-04`	Mirroring blobs	Replicating a blob from one server to another (PUT /mirror) so it is not tied to a single host.
`BUD-05`	Media optimization	Endpoints for server-side media processing / optimization of uploaded content.
`BUD-06`	Upload requirements	Pre-flight validation of an upload before the bytes are sent.
`BUD-07`	Payment required	How a server operator can require payment for storage (monetization).
`BUD-08`	Nostr File Metadata Tags	Standardized Nostr tags for describing a stored file’s metadata.
`BUD-09`	Blob Report	A protocol for reporting problematic or abusive blobs to a server.
`BUD-10`	Blossom URI schema	A URI format for referencing a Blossom blob.
`BUD-11`	Nostr Authorization	Authenticating requests using Nostr keys (signed authorization events).
`BUD-12`	Blob management endpoints	Listing and deleting the blobs a user has stored on a server.

Why it matters for a sovereign stack

Nostr handles the notes; Blossom handles the blobs those notes point at. Because a blob is addressed by its hash and your server list is your own Nostr event, you can mirror your media across several servers and move hosts without breaking links — the same content-addressed, host-independent idea that makes the rest of the sovereign stack resilient.

Nostr key management · Nostr event-kinds reference · Nostr relay directory · Meshtastic PortNum registry (the mesh analogue) · the sovereignty hub.

Credit: Blossom is designed and maintained by hzrd149 and the Nostr community; this page is a dated, human-readable index of the project’s BUD specs.

Related products, repair, and setup paths

Last reviewed July 21, 2026.