Solid Protocol

Solid is the protocol behind personal data pods: a server holds a person’s data as a tree of resources, applications are granted access to parts of that tree, and the person can move the whole thing to another server. The specification is deliberately a composition of existing pieces rather than a new wire format, which is what makes it interesting as prior art.

• Containers are LDP Basic Containers - Directories, listing, POST to create, PUT and PATCH to write, DELETE to remove, ETag preconditions on updates. All inherited from the Linked Data Platform.
• Authorization per resource - Servers must implement Web Access Control or Access Control Policy, so a client’s permission is a scope over a namespace rather than a token for the whole server.
• Solid Notifications Protocol - A client discovers subscription resources, subscribes to a resource or a container, and receives change notifications over WebSocket or webhook. Change notification is part of the protocol, not an add-on.
• Identity via WebID and OIDC - Who is asking is settled by Solid-OIDC, and the answer travels with every request.

What Solid got right, and what nobody else packaged together, is the shape of the delegation: here is a namespace, here is what you may do in it, and here is how you will hear when it changes. That is almost exactly the shape agent platforms arrived at in 2026 when they started mounting remote services for a model to work in, and it is the shape the Model Context Protocol file-system work is circling. Solid never got adoption at scale, and it is still a community group draft rather than a W3C standard, but it is the most complete written version of the idea. I would rather point a working group at it than watch the idea be rediscovered one primitive at a time.