Building an MCP Client

The MCP Inspector is great for manual exploration, but real integrations need a programmatic client. In this lesson you write a client from scratch in your chosen language and verify it can connect to a server, list capabilities, and invoke tools.

Learning objectives

By the end of this lesson you will be able to:

Understand what an MCP client does and why you need one
Write a client that connects to an MCP server over stdio
List and invoke tools, resources, and prompts programmatically
Run both client and server together in a local workflow

What a client does

An MCP client:

Imports the MCP SDK and a transport module
Instantiates a transport that knows how to start the server process
Creates a Client object and connects it to the transport
Calls listTools, listResources, listPrompts to discover server capabilities
Calls callTool, readResource, getPrompt to invoke them

Example client

import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";

const transport = new StdioClientTransport({
  command: "node",
  args: ["build/index.js"]
});

const client = new Client({ name: "example-client", version: "1.0.0" });
await client.connect(transport);

// List capabilities
const tools = await client.listTools();
const resources = await client.listResources();
const prompts = await client.listPrompts();

// Call a tool
const result = await client.callTool({
  name: "add",
  arguments: { a: 5, b: 3 }
});

// Read a resource
const resource = await client.readResource({ uri: "greeting://world" });

// Get a prompt
const prompt = await client.getPrompt({
  name: "review-code",
  arguments: { code: "console.log('hello')" }
});

Step-by-step walkthrough

Import the libraries

You need two things: the Client class and a transport. For local servers, use stdio transport. For HTTP servers, use SSE or Streamable HTTP transport.

TypeScript
Python

import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";

from mcp import ClientSession, StdioServerParameters, types
from mcp.client.stdio import stdio_client

Instantiate client and transport

The stdio transport takes command and args — the exact command used to start the server process. The client connects through that transport.

TypeScript
Python

const transport = new StdioClientTransport({
  command: "node",
  args: ["server.js"]
});

const client = new Client({ name: "example-client", version: "1.0.0" });
await client.connect(transport);

server_params = StdioServerParameters(
    command="mcp",
    args=["run", "server.py"],
)

async with stdio_client(server_params) as (read, write):
    async with ClientSession(read, write) as session:
        await session.initialize()

List server capabilities

TypeScript
Python
.NET
Java

const tools = await client.listTools();
const resources = await client.listResources();
const prompts = await client.listPrompts();

resources = await session.list_resources()
tools = await session.list_tools()
for tool in tools.tools:
    print("Tool:", tool.name)

foreach (var tool in await mcpClient.ListToolsAsync())
    Console.WriteLine($"{tool.Name} ({tool.Description})");

ListToolsResult toolsList = client.listTools();
System.out.println("Available Tools = " + toolsList);
client.ping(); // verify connection

Invoke features

TypeScript
Python
.NET
Java

// Call a tool
const result = await client.callTool({
  name: "add",
  arguments: { a: 5, b: 3 }
});

// Read a resource
const resource = await client.readResource({
  uri: "greeting://world"
});

// Get a prompt
const promptResult = await client.getPrompt({
  name: "review-code",
  arguments: { code: "console.log('hello')" }
});

# Read a resource
content, mime_type = await session.read_resource("greeting://hello")

# Call a tool
result = await session.call_tool("add", arguments={"a": 1, "b": 7})
print(result.content)

var result = await mcpClient.CallToolAsync(
    "Add",
    new Dictionary<string, object?>() { ["a"] = 1, ["b"] = 3 },
    cancellationToken: CancellationToken.None);
Console.WriteLine(result.Content.First(c => c.Type == "text").Text);
// Sum 4

CallToolResult resultAdd = client.callTool(
    new CallToolRequest("add", Map.of("a", 5.0, "b", 3.0)));
CallToolResult resultSubtract = client.callTool(
    new CallToolRequest("subtract", Map.of("a", 10.0, "b", 4.0)));
System.out.println("Subtract Result = " + resultSubtract);

Run the client

TypeScript
Python
.NET
Java

Add to package.json scripts: "client": "tsc && node build/client.js", then:

npm run client

python client.py

dotnet run

./mvnw clean compile
./mvnw exec:java -Dexec.mainClass="com.microsoft.mcp.sample.client.SDKClient"

You should see output similar to:

Prompt: Please review this code: console.log("hello");
Resource template: file
Tool result: { content: [ { type: 'text', text: '9' } ] }

Key takeaways

A client can discover and invoke any capability on a server — tools, resources, and prompts.
The stdio transport starts the server as a child process, so you don’t need to manage it separately.
A programmatic client is ideal for automated workflows and CI/CD pipelines.
In the next lesson, you’ll add an LLM to the client so users interact via natural language.

Get Started

Foundation

Building Your First Server

Practical & Advanced

Community & Best Practices

Learning objectives

What a client does

Example client

Step-by-step walkthrough

Key takeaways

Build docs developers (and LLMs) love

Get Started

Foundation

Building Your First Server

Practical & Advanced

Community & Best Practices

​Learning objectives

​What a client does

​Example client

​Step-by-step walkthrough

​Key takeaways

Build docs developers (and LLMs) love

Learning objectives

What a client does

Example client

Step-by-step walkthrough

Key takeaways