# How a Host Uses MCP Servers — MCP & Agent-to-Agent Protocols

Source: https://www.geekswithgeeks.com/en/mcp-a2a/c-host

> Follow the flow from configuration to a tool call.

## Configure, initialise, expose, execute

A host reads its configuration (a list of servers: a command to launch for stdio, or a URL for HTTP, plus environment variables), starts or connects to each server, performs the **initialize** handshake, and calls `tools/list` (following pagination). It then merges the tool definitions into what the model can see, often **prefixing names by server** to avoid clashes. When the model requests a call, the host **checks policy and asks the user** if required, sends `tools/call` to the right client, and returns the result to the model. The host also handles **list-changed notifications**, reconnects, timeouts and cancellation. Good hosts let users enable or disable individual tools and servers.

## Connect, expose, approve

A host connects to servers, shows the model a curated tool list and keeps the user in control.

![Three duties: connect, curate, consent.](assets/figures/mcp-a2a/section-4-map.svg) — Figure 4.1 — Connect, curate and consent.

## A typical server configuration (illustrative)

The file format and location differ between hosts; the idea is a named server with a launch command and environment. Not run here.

```json
{
  "mcpServers": {
    "orders": {
      "command": "python",
      "args": ["server.py"],
      "env": { "ORDERS_DB_URL": "<set via a secret store, not committed>" }
    },
    "docs": { "url": "https://mcp.example.com/docs" }
  }
}
```

**Quiz:** Why might a host prefix tool names with the server name?

- [ ] To train the model
- [ ] To compress tool descriptions
- [ ] To skip the handshake
- [x] To avoid name clashes between servers

*Answer:* To avoid name clashes between servers. Two servers may both define a tool with the same name.