alt Hacker NewsKind of--I'm saying that RESTful APIs are just an abstract vocabulary to describe state transfer operations, whereas MCP describes a concrete set of such operations. REST sits on top of the HTTP protocol layer, MCP sits on top of REST (if we accept how the meaning of REST has been butchered, but you know what I mean.)
This is easy to see when you think in terms of a client: It is pretty much impossible to build an opinionated UI for any kind of RESTful API, while creating one for an MCP server is fairly self-explanatory: MCP servers offer a mandatory and complete runtime introspection endpoint (you can retrieve a listing of available tools/resources/prompts etc. along with their parameter and return type schemas). So that means clients have a way to exhaustively describe everything an MCP server is able to do with a vocabulary that carries over exactly to other servers - a tool is a tool everywhere.
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I think OpenAPI does all you mentioned in your comment too. Maybe MCP is more strict, in the sense that it requires natural-language descriptions, which are optional in OpenAPI, but I don’t see the distinction.
There are multiple products that turn OpenAPI schemas into front-ends nowadays.
See my point #2. There are already standards to describe APIs.
This is easy to see when you think in terms of a developer. The natural way to adapt an existing REST API into an MCP server while keeping the two synchronized is to simply write a basic translation tool that takes your OpenAPI spec and turns it into an MCP manifest, mapping each HTTP endpoint to an MCP method, and copying over all the request / response type signatures and descriptions for everything. Then, all of the sudden, it hits you: there is no need for this translation layer.