How MCP Clients Connect Servers to Claude

The MCP client serves as the communication bridge between your application and an MCP server. It is your access point to all the tools, resources, and prompts that an MCP server provides, and it handles the message exchange and protocol details so your application code does not have to. In practice, the MCP client exposes a clean interface to your code: you ask it for the list of available tools, you ask it to execute a specific tool, and the client takes care of formatting the requests, sending them over the chosen transport, and parsing the responses. This abstraction lets you focus on your application logic instead of the protocol's wire format.

One of MCP's key strengths is being transport agnostic, which is a fancy way of saying the client and server can communicate over different protocols depending on your setup. The most common configuration runs both the MCP client and server on the same machine, communicating through standard input and output. But you can also connect them over HTTP, including a streamable HTTP transport for remote servers, and over various other network protocols. This flexibility means the same MCP server implementation can work in a local development setup, in a production deployment over a network, or embedded into a desktop application, without rewriting the server's logic.

Once an MCP client and server are connected, they exchange specific message types defined in the MCP specification. The two main ones you will work with are: a list tools request with its corresponding list tools result, where the client asks the server what tools do you provide and gets back a list of available tools. And a call tool request with its corresponding call tool result, where the client asks the server to run a specific tool with given arguments and then receives the results. There are similar request and result pairs for resources and prompts, but tools are the most common starting point when you first work with the protocol.

Let's trace a complete example. A user asks what repositories do I have. First, your server receives the query and needs to know what tools are available, so it asks the MCP client for them. The MCP client sends a list tools request to the MCP server and receives a list tools result. Your server then sends the user's query plus the available tools to Claude. Claude decides it needs to call a tool, so your server asks the MCP client to run it. The client sends a call tool request, the MCP server makes the actual GitHub API call, and the result flows back as a call tool result. Finally, your server sends the tool results back to Claude, who formulates the answer for the user.

Yes, the full flow involves many steps, but each component has a clear responsibility. Your application handles user-facing logic. The MCP client abstracts away the complexity of server communication, including the protocol's wire format, the transport choice, and the message exchange. The MCP server owns the integration with one external service. Claude itself owns the reasoning about which tool to call and how to interpret results. This separation means each piece can evolve independently. You can swap one MCP server for another, change transport without touching your application code, or update Claude's behavior without rewriting integrations.