What is MCP? The Model Context Protocol, explained
MCP (Model Context Protocol) is an open standard that lets an AI agent connect to a tool or data source through one consistent interface, the way a USB port connects any device.
An AI agent is only as useful as the tools it can reach. Before MCP, every connection between a model and a tool was a one-off: a custom function, a bespoke schema, glue code that broke when either side changed. Ten tools across three agents meant thirty integrations to write and maintain.
MCP fixes the shape of that problem. It defines one protocol for how an agent asks what a tool can do, calls it, and reads the result. Build a tool as an MCP server once, and any MCP client can use it. Wire an agent to speak MCP once, and it can use any MCP server. The common comparison is a USB port: the port does not care what you plug in, and the device does not care what it plugs into, because both agree on the interface.
#What an MCP server exposes
A server advertises three kinds of thing:
- Tools: actions the agent can invoke, like "search the web" or "create an invoice," each with a typed input schema.
- Resources: data the agent can read, like a file, a database row, or a document.
- Prompts: reusable prompt templates the server offers for common tasks.
The agent discovers these at connection time, so it learns the tool's capabilities instead of having them hard-coded.
#Why it caught on
Two forces. Agents got good enough that people wanted to give them real tools, and the integration cost was the bottleneck. MCP turned an N-times-M problem (every agent times every tool) into N-plus-M (each side implements the protocol once). Search volume for "mcp server" went from near zero to tens of thousands a month within a year, which tells you how fast developers adopted it.
#Where StackResolve fits
We score how ready a tool is for an agent to use, and whether it publishes an MCP server is part of that. Browse MCP infrastructure tools ranked by AgentReady score, or check any tool's profile to see if it ships an MCP server and how an agent connects.