What is an MCP server?
The program that turns a piece of software into something an AI agent can actually operate.
MCP server — An MCP server is a program that publishes a set of tools, resources and prompts in the Model Context Protocol so that MCP clients such as Claude, ChatGPT or Cursor can discover and call them. Its purpose is to make a system usable by agents without custom code per model.
Also known as: MCP host
Why it matters
An MCP server is the half of the protocol that does the work. The client (Claude, ChatGPT, Cursor) asks what tools exist and calls them; the server is the program that answers, holds the real data, and carries out the action. Without a server, a client has nothing to connect to.
For a sales team, the server is what lets "ask Claude to check on this deal" become "ask Claude to move this deal, draft the follow-up and queue it." The quality of that experience depends entirely on how much of the real system the server exposes. A server with five tools covering only contact lookups is not much more useful than search; a server that covers pipeline, inbox, outreach and approvals is a different product. SalesCrew's MCP server registers over 140 tools, one for nearly every action available in the app, scoped by the same access rules as the UI.
What a server does, end to end
- 1
It registers its tools
Each tool is declared with a name, a description and the arguments it needs.
- 2
A client connects and lists them
Claude or another client asks the server what it can do.
- 3
A call arrives with arguments
The model has decided to run one tool and supplies the values it needs.
- 4
The server checks permissions
It confirms the caller, a user or a token, is scoped to take that action.
- 5
It executes and returns a result
The action runs against the real database and the outcome goes back to the client.
The mistake to watch for
Questions
- How is an MCP server different from an MCP client?
- The server publishes tools and executes them against real data; the client, whether Claude, ChatGPT or Cursor, discovers those tools and decides when to call them. A server without a client has nothing to talk to it; a client without a server has nothing to call.
- Can one MCP server work with more than one AI client?
- Yes, and that is the point of the standard. A server built once can be connected to Claude, ChatGPT, Cursor or any other compliant client without separate integration work for each.
- Does an MCP server need its own permission system?
- Yes. The protocol itself does not define access control, so a server has to check who is calling, whether a user or a scoped token, and only allow the actions that caller is permitted to take, logging the result.