They didn't reinvent it, it's literally using JSONRPC. The thing they "invented" was coming up with a loose standard for how to implement your RPC endpoints in a way that the AI was pre-trained to interact with.
The actual implementation may have been very janky but the idea itself is sound: If you want to interact with arbitrary services then providing one single protocol (ideally not JSONRPC but hey) with a standard api discovery method and standard starting method call means your super-intelligent machine god can connect to any MCP service with just a URL and figure everything out from there.
> was coming up with a loose standard for how to implement your RPC endpoints in a way that the AI was pre-trained to interact with.
Why not just pre-train the model to interact with JSONRPC endpoints?
There's more to it than that. MCP adds the concept of the API endpoints describing themselves (giving agents context), standardizes how auth works, and so on. This could all be done by packaging existing standards, but MCP in many ways is packaging and organizing existing standards, minus the previous stateful-first design.
I do think a lot of the standard would have been easier if they'd been stateless first, and allowed for GET requests, but it evolved from a starting point that has since evolved.
MCP is invisible to the LLM, or should be, under normal use
Not sure I understand what you mean. MCP servers and methods available do have to be visible to the model in some way so that it can spit out tool calls instructions to be executed by the orchestration layer around it. But you probably meant something else?
MCP is the protocol by which the harness can connect with additional tools. The harness does the work of discovering the tools, the model is then fed a description of what tools it has available, with zero awareness of whether those tools are MCP or built into the harness itself (except for by the mcp__ prefix in the tool’s name, which a harness could choose to strip off)
By this statement, do you mean that LLMs really just know about "Tool Calling Tokens" or something else?
Essentially, MCP is the harness’ wheelhouse, not the model’s