Introduction

We’ve covered what MCP is, how it connects to systems, and how it enables agent workflows. Now, let’s get hands-on.

This guide will show you how to build your first MCP server and how to test/debug it.

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Building Your First MCP Server

An MCP server exposes your system (database, API, or service) to an agent. At a glance:

1. Define capabilities – decide what your server can do (e.g., list files).
2. Implement endpoints – follow the MCP protocol to expose them.
3. Run and test – so an MCP-aware agent (or developer tools) can use it.

Example Project: File System MCP Server in Go

A working example is available in this GitHub repo:
👉 inside-mcp/cmd/first/main.go

To try it out:

# Clone the repo
git clone https://github.com/tendant/inside-mcp.git
cd inside-mcp/cmd/first

# Run the server (using the current directory as root by default)
go run .

# Or, set a custom root directory:
MCP_FS_ROOT=/path/to/folder go run .

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Testing & Debugging MCP Integrations

MCP servers communicate via JSON-RPC over stdio. Here’s how to test one in practice:

1. Build the server

go build cmd/first/main.go -o first

2. Install mcptools

go install github.com/f/mcptools/cmd/mcptools@latest

3. Use mcptools to explore your server

mcptools tools ./first
mcptools call list_resources ./first

This shows the tools your server exposes and lets you call them directly.

4. Send raw JSON (optional)

You can also pipe JSON directly:

echo '{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "list_roots",
    "arguments": {}
  }
}' | ./first

5. Unit test handlers directly

func TestListResources(t *testing.T) {
    args := ResourceParams{Path: "."}
    res, data, err := listResources(context.Background(), nil, args)
    if err != nil {
        t.Fatal(err)
    }
    if len(data.([]string)) == 0 {
        t.Fatal("expected files, got none")
    }
}

6. Use the server with Claude Desktop

Claude Desktop supports MCP servers out of the box. To connect your server:

1. Open the Claude Desktop config file:

   • macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
   • Windows: %AppData%/Claude/claude_desktop_config.json

2. Add an entry for your MCP server, for example:

   {
     "mcpServers": {
       "filesystem": {
         "command": "/absolute/path/to/first"
       }
     }
   }

   Replace /absolute/path/to/first with the path to the binary you built earlier.

3. Restart Claude Desktop.

Now you can chat with Claude and say:
“List the files in my home directory.”
Claude will call your list_resources tool through MCP and return the results.

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Wrapping Up

The simplest path to an MCP integration:

1. Build a server (we used Go + the MCP SDK).
2. Run it with a system to expose.
3. Test it with mcptools, raw JSON, or unit tests.
4. Connect it to Claude Desktop to see it in action with a real agent.

With this workflow, you can start small and gradually expand your integration.

In the next article, we’ll explore advanced MCP patterns—scaling multi-agent setups, monitoring traffic, and cross-organization integrations.