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11 KiB
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430 lines
No EOL
11 KiB
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---
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title: "Building MCP clients"
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description: "Learn how to build your first client in MCP"
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---
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In this tutorial, you'll learn how to build a LLM-powered chatbot client that connects to MCP servers. It helps to have gone through the [Quickstart tutorial](/quickstart) that guides you through the basic of building your first server.
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<Tabs>
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<Tab title="Python">
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You can find the complete code for this tutorial [here.](https://gist.github.com/zckly/f3f28ea731e096e53b39b47bf0a2d4b1)
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## System Requirements
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Before starting, ensure your system meets these requirements:
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- Mac or Windows computer
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- Latest Python version installed
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- Latest version of `uv` installed
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## Setting Up Your Environment
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First, create a new Python project with `uv`:
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```bash
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# Create project directory
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uv init mcp-client
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cd mcp-client
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# Create virtual environment
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uv venv
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# Activate virtual environment
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# On Windows:
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.venv\Scripts\activate
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# On Unix or MacOS:
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source .venv/bin/activate
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# Install required packages
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uv add mcp anthropic python-dotenv
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# Remove boilerplate files
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rm hello.py
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# Create our main file
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touch client.py
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```
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## Setting Up Your API Key
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You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
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Create a `.env` file to store it:
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```bash
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# Create .env file
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touch .env
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```
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Add your key to the `.env` file:
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```bash
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ANTHROPIC_API_KEY=<your key here>
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```
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Add `.env` to your `.gitignore`:
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```bash
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echo ".env" >> .gitignore
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```
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<Warning>
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Make sure you keep your `ANTHROPIC_API_KEY` secure!
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</Warning>
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## Creating the Client
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### Basic Client Structure
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First, let's set up our imports and create the basic client class:
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```python
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import asyncio
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from typing import Optional
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from contextlib import AsyncExitStack
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from mcp import ClientSession, StdioServerParameters
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from mcp.client.stdio import stdio_client
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from anthropic import Anthropic
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from dotenv import load_dotenv
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load_dotenv() # load environment variables from .env
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class MCPClient:
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def __init__(self):
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# Initialize session and client objects
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self.session: Optional[ClientSession] = None
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self.exit_stack = AsyncExitStack()
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self.anthropic = Anthropic()
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# methods will go here
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```
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### Server Connection Management
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Next, we'll implement the method to connect to an MCP server:
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```python
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async def connect_to_server(self, server_script_path: str):
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"""Connect to an MCP server
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Args:
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server_script_path: Path to the server script (.py or .js)
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"""
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is_python = server_script_path.endswith('.py')
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is_js = server_script_path.endswith('.js')
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if not (is_python or is_js):
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raise ValueError("Server script must be a .py or .js file")
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command = "python" if is_python else "node"
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server_params = StdioServerParameters(
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command=command,
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args=[server_script_path],
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env=None
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)
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stdio_transport = await self.exit_stack.enter_async_context(stdio_client(server_params))
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self.stdio, self.write = stdio_transport
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self.session = await self.exit_stack.enter_async_context(ClientSession(self.stdio, self.write))
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await self.session.initialize()
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# List available tools
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response = await self.session.list_tools()
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tools = response.tools
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print("\nConnected to server with tools:", [tool.name for tool in tools])
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```
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### Query Processing Logic
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Now let's add the core functionality for processing queries and handling tool calls:
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```python
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async def process_query(self, query: str) -> str:
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"""Process a query using Claude and available tools"""
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messages = [
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{
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"role": "user",
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"content": query
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}
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]
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response = await self.session.list_tools()
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available_tools = [{
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"name": tool.name,
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"description": tool.description,
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"input_schema": tool.inputSchema
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} for tool in response.tools]
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# Initial Claude API call
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response = self.anthropic.messages.create(
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model="claude-3-5-sonnet-20241022",
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max_tokens=1000,
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messages=messages,
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tools=available_tools
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)
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# Process response and handle tool calls
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tool_results = []
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final_text = []
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for content in response.content:
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if content.type == 'text':
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final_text.append(content.text)
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elif content.type == 'tool_use':
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tool_name = content.name
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tool_args = content.input
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# Execute tool call
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result = await self.session.call_tool(tool_name, tool_args)
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tool_results.append({"call": tool_name, "result": result})
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final_text.append(f"[Calling tool {tool_name} with args {tool_args}]")
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# Continue conversation with tool results
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if hasattr(content, 'text') and content.text:
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messages.append({
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"role": "assistant",
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"content": content.text
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})
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messages.append({
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"role": "user",
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"content": result.content
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})
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# Get next response from Claude
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response = self.anthropic.messages.create(
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model="claude-3-5-sonnet-20241022",
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max_tokens=1000,
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messages=messages,
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)
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final_text.append(response.content[0].text)
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return "\n".join(final_text)
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```
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### Interactive Chat Interface
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Now we'll add the chat loop and cleanup functionality:
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```python
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async def chat_loop(self):
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"""Run an interactive chat loop"""
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print("\nMCP Client Started!")
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print("Type your queries or 'quit' to exit.")
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while True:
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try:
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query = input("\nQuery: ").strip()
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if query.lower() == 'quit':
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break
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response = await self.process_query(query)
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print("\n" + response)
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except Exception as e:
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print(f"\nError: {str(e)}")
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async def cleanup(self):
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"""Clean up resources"""
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await self.exit_stack.aclose()
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```
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### Main Entry Point
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Finally, we'll add the main execution logic:
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```python
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async def main():
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if len(sys.argv) < 2:
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print("Usage: python client.py <path_to_server_script>")
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sys.exit(1)
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client = MCPClient()
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try:
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await client.connect_to_server(sys.argv[1])
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await client.chat_loop()
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finally:
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await client.cleanup()
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if __name__ == "__main__":
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import sys
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asyncio.run(main())
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```
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You can find the complete `client.py` file [here.](https://gist.github.com/zckly/f3f28ea731e096e53b39b47bf0a2d4b1)
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## Key Components Explained
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### 1. Client Initialization
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- The `MCPClient` class initializes with session management and API clients
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- Uses `AsyncExitStack` for proper resource management
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- Configures the Anthropic client for Claude interactions
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### 2. Server Connection
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- Supports both Python and Node.js servers
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- Validates server script type
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- Sets up proper communication channels
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- Initializes the session and lists available tools
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### 3. Query Processing
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- Maintains conversation context
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- Handles Claude's responses and tool calls
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- Manages the message flow between Claude and tools
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- Combines results into a coherent response
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### 4. Interactive Interface
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- Provides a simple command-line interface
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- Handles user input and displays responses
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- Includes basic error handling
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- Allows graceful exit
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### 5. Resource Management
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- Proper cleanup of resources
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- Error handling for connection issues
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- Graceful shutdown procedures
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## Common Customization Points
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1. **Tool Handling**
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- Modify `process_query()` to handle specific tool types
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- Add custom error handling for tool calls
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- Implement tool-specific response formatting
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2. **Response Processing**
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- Customize how tool results are formatted
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- Add response filtering or transformation
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- Implement custom logging
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3. **User Interface**
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- Add a GUI or web interface
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- Implement rich console output
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- Add command history or auto-completion
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## Running the Client
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To run your client with any MCP server:
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```bash
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uv run client.py path/to/server.py # python server
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uv run client.py path/to/build/index.js # node server
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```
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<Note>
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If you're continuing the weather tutorial from the quickstart, your command might look something like this: `python client.py .../weather/src/weather/server.py`
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</Note>
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The client will:
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1. Connect to the specified server
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2. List available tools
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3. Start an interactive chat session where you can:
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- Enter queries
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- See tool executions
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- Get responses from Claude
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Here's an example of what it should look like if connected to the weather server from the quickstart:
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<Frame>
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<img src="/images/client-claude-cli-python.png" />
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</Frame>
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## How It Works
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When you submit a query:
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1. The client gets the list of available tools from the server
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2. Your query is sent to Claude along with tool descriptions
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3. Claude decides which tools (if any) to use
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4. The client executes any requested tool calls through the server
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5. Results are sent back to Claude
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6. Claude provides a natural language response
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7. The response is displayed to you
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## Best practices
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1. **Error Handling**
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- Always wrap tool calls in try-catch blocks
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- Provide meaningful error messages
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- Gracefully handle connection issues
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2. **Resource Management**
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- Use `AsyncExitStack` for proper cleanup
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- Close connections when done
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- Handle server disconnections
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3. **Security**
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- Store API keys securely in `.env`
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- Validate server responses
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- Be cautious with tool permissions
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## Troubleshooting
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### Server Path Issues
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- Double-check the path to your server script is correct
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- Use the absolute path if the relative path isn't working
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- For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
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- Verify the server file has the correct extension (.py for Python or .js for Node.js)
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Example of correct path usage:
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```bash
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# Relative path
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uv run client.py ./server/weather.py
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# Absolute path
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uv run client.py /Users/username/projects/mcp-server/weather.py
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# Windows path (either format works)
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uv run client.py C:/projects/mcp-server/weather.py
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uv run client.py C:\\projects\\mcp-server\\weather.py
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```
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### Response Timing
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- The first response might take up to 30 seconds to return
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- This is normal and happens while:
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- The server initializes
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- Claude processes the query
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- Tools are being executed
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- Subsequent responses are typically faster
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- Don't interrupt the process during this initial waiting period
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### Common Error Messages
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If you see:
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- `FileNotFoundError`: Check your server path
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- `Connection refused`: Ensure the server is running and the path is correct
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- `Tool execution failed`: Verify the tool's required environment variables are set
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- `Timeout error`: Consider increasing the timeout in your client configuration
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</Tab>
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</Tabs>
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## Next steps
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<CardGroup cols={2}>
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<Card
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title="Example servers"
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icon="grid"
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href="/examples"
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>
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Check out our gallery of official MCP servers and implementations
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</Card>
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<Card
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title="Clients"
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icon="cubes"
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href="/clients"
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>
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View the list of clients that support MCP integrations
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</Card>
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<Card
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title="Building MCP with LLMs"
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icon="comments"
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href="/building-mcp-with-llms"
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>
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Learn how to use LLMs like Claude to speed up your MCP development
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</Card>
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<Card
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title="Core architecture"
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icon="sitemap"
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href="/docs/concepts/architecture"
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>
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Understand how MCP connects clients, servers, and LLMs
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</Card>
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</CardGroup> |