MCP server
A small program that exposes tools or data to a model through the Model Context Protocol, a shared standard for how harnesses connect to tools. Instead of hard-coding an integration, you point the harness at an MCP server and the model can call whatever it offers: files, a database, an API. One protocol, many pluggable tools.
Nothing new happens at the model. The harness asks the server what tools it has, writes that list into the prompt the same way it writes its own built-in tools, and runs whatever the model asks for. The protocol is about how the harness and the tool find each other, not about how the model thinks.
The practical effect is that memory and integrations stop being something a vendor has to build into a product. A server that searches your old conversations is a few hundred lines, and any harness that speaks the protocol can use it, including one pointed at a model on your own machine.