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@ -5,35 +5,42 @@ description: "Learn how to build your first client in MCP"
In this tutorial, you'll learn how to build a client application 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.
<Tabs>
<Tab title="Python">
## System Requirements
Before starting, ensure your system meets these requirements:
- Mac or Windows computer
- Latest Python version installed
- Latest version of `uv` installed
## Setting Up Your Environment
First, create and activate a virtual environment:
First, create a new Python project with `uv`:
```bash
# Install virtualenv if needed
pip install virtualenv
# Create project directory
mkdir mcp-client
uv init mcp-client
cd mcp-client
# Create virtual environment
python -m virtualenv venv
uv venv
# Activate virtual environment
# On Windows:
venv\Scripts\activate
.venv\Scripts\activate
# On Unix or MacOS:
source venv/bin/activate
source .venv/bin/activate
# Install required packages
pip install mcp anthropic python-dotenv
uv add mcp anthropic python-dotenv
# Remove boilerplate files
rm hello.py
# Create our main file
touch client.py
```
## Setting Up Your API Key
@ -57,9 +64,14 @@ Add `.env` to your `.gitignore`:
echo ".env" >> .gitignore
```
<Warning>
Make sure you keep your `ANTHROPIC_API_KEY` secure!
</Warning>
## Creating the Client
Let's create a Python client that can connect to any MCP server. We'll call it `client.py`:
### Basic Client Structure
First, let's set up our imports and create the basic client class:
```python
import asyncio
@ -80,110 +92,144 @@ class MCPClient:
self.session: Optional[ClientSession] = None
self.exit_stack = AsyncExitStack()
self.anthropic = Anthropic()
# methods will go here
```
async def connect_to_server(self, server_script_path: str):
"""Connect to an MCP server"""
server_params = StdioServerParameters(
command="python",
args=[server_script_path],
env=None
)
stdio_transport = await self.exit_stack.enter_async_context(stdio_client(server_params))
self.stdio, self.write = stdio_transport
self.session = await self.exit_stack.enter_async_context(ClientSession(self.stdio, self.write))
await self.session.initialize()
# List available tools
response = await self.session.list_tools()
tools = response.tools
print("\nConnected to server with tools:", [tool.name for tool in tools])
### Server Connection Management
async def process_query(self, query: str) -> str:
"""Process a query using Claude and available tools"""
messages = [
{
"role": "user",
"content": query
}
]
Next, we'll implement the method to connect to an MCP server:
response = await self.session.list_tools()
available_tools = [{
"name": tool.name,
"description": tool.description,
"input_schema": tool.inputSchema
} for tool in response.tools]
# Initial Claude API call
response = self.anthropic.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1000,
messages=messages,
tools=available_tools
)
# Process response and handle tool calls
tool_results = []
final_text = []
for content in response.content:
if content.type == 'text':
final_text.append(content.text)
elif content.type == 'tool_use':
tool_name = content.name
tool_args = content.input
# Execute tool call
result = await self.session.call_tool(tool_name, tool_args)
tool_results.append({"call": tool_name, "result": result})
final_text.append(f"[Calling tool {tool_name} with args {tool_args}]")
# Continue conversation with tool results
if hasattr(content, 'text') and content.text:
messages.append({
"role": "assistant",
"content": content.text
})
messages.append({
"role": "user",
"content": result.content
})
# Get next response from Claude
response = self.anthropic.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1000,
messages=messages,
)
final_text.append(response.content[0].text)
return "\n".join(final_text)
async def chat_loop(self):
"""Run an interactive chat loop"""
print("\nMCP Client Started!")
print("Type your queries or 'quit' to exit.")
while True:
try:
query = input("\nQuery: ").strip()
if query.lower() == 'quit':
break
response = await self.process_query(query)
print("\n" + response)
except Exception as e:
print(f"\nError: {str(e)}")
```python
async def connect_to_server(self, server_script_path: str):
"""Connect to an MCP server
async def cleanup(self):
"""Clean up resources"""
await self.exit_stack.aclose()
Args:
server_script_path: Path to the server script (.py or .js)
"""
is_python = server_script_path.endswith('.py')
is_js = server_script_path.endswith('.js')
if not (is_python or is_js):
raise ValueError("Server script must be a .py or .js file")
command = "python" if is_python else "node"
server_params = StdioServerParameters(
command=command,
args=[server_script_path],
env=None
)
stdio_transport = await self.exit_stack.enter_async_context(stdio_client(server_params))
self.stdio, self.write = stdio_transport
self.session = await self.exit_stack.enter_async_context(ClientSession(self.stdio, self.write))
await self.session.initialize()
# List available tools
response = await self.session.list_tools()
tools = response.tools
print("\nConnected to server with tools:", [tool.name for tool in tools])
```
### Query Processing Logic
Now let's add the core functionality for processing queries and handling tool calls:
```python
async def process_query(self, query: str) -> str:
"""Process a query using Claude and available tools"""
messages = [
{
"role": "user",
"content": query
}
]
response = await self.session.list_tools()
available_tools = [{
"name": tool.name,
"description": tool.description,
"input_schema": tool.inputSchema
} for tool in response.tools]
# Initial Claude API call
response = self.anthropic.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1000,
messages=messages,
tools=available_tools
)
# Process response and handle tool calls
tool_results = []
final_text = []
for content in response.content:
if content.type == 'text':
final_text.append(content.text)
elif content.type == 'tool_use':
tool_name = content.name
tool_args = content.input
# Execute tool call
result = await self.session.call_tool(tool_name, tool_args)
tool_results.append({"call": tool_name, "result": result})
final_text.append(f"[Calling tool {tool_name} with args {tool_args}]")
# Continue conversation with tool results
if hasattr(content, 'text') and content.text:
messages.append({
"role": "assistant",
"content": content.text
})
messages.append({
"role": "user",
"content": result.content
})
# Get next response from Claude
response = self.anthropic.messages.create(
model="claude-3-5-sonnet-20241022",
max_tokens=1000,
messages=messages,
)
final_text.append(response.content[0].text)
return "\n".join(final_text)
```
### Interactive Chat Interface
Now we'll add the chat loop and cleanup functionality:
```python
async def chat_loop(self):
"""Run an interactive chat loop"""
print("\nMCP Client Started!")
print("Type your queries or 'quit' to exit.")
while True:
try:
query = input("\nQuery: ").strip()
if query.lower() == 'quit':
break
response = await self.process_query(query)
print("\n" + response)
except Exception as e:
print(f"\nError: {str(e)}")
async def cleanup(self):
"""Clean up resources"""
await self.exit_stack.aclose()
```
### Main Entry Point
Finally, we'll add the main execution logic:
```python
async def main():
if len(sys.argv) < 2:
print("Usage: python client.py <path_to_server_script>")
@ -201,31 +247,62 @@ if __name__ == "__main__":
asyncio.run(main())
```
## Understanding the Client Code
You can find the complete `client.py` file [here.](https://gist.github.com/zckly/f3f28ea731e096e53b39b47bf0a2d4b1)
Let's break down the key components of our MCP client:
## Key Components Explained
1. **MCPClient Class**
- Manages the connection to the MCP server
- Handles communication between Claude and the server's tools
- Maintains the chat session
### 1. Client Initialization
- The `MCPClient` class initializes with session management and API clients
- Uses `AsyncExitStack` for proper resource management
- Configures the Anthropic client for Claude interactions
2. **Key Methods**
- `connect_to_server()`: Establishes connection with an MCP server
- `process_query()`: Handles user queries by:
- Getting available tools from the server
- Sending the query to Claude with tool information
- Executing any tool calls Claude requests
- Processing Claude's responses
- `chat_loop()`: Runs the interactive chat interface
- `cleanup()`: Properly closes connections and resources
### 2. Server Connection
- Supports both Python and Node.js servers
- Validates server script type
- Sets up proper communication channels
- Initializes the session and lists available tools
### 3. Query Processing
- Maintains conversation context
- Handles Claude's responses and tool calls
- Manages the message flow between Claude and tools
- Combines results into a coherent response
### 4. Interactive Interface
- Provides a simple command-line interface
- Handles user input and displays responses
- Includes basic error handling
- Allows graceful exit
### 5. Resource Management
- Proper cleanup of resources
- Error handling for connection issues
- Graceful shutdown procedures
## Common Customization Points
1. **Tool Handling**
- Modify `process_query()` to handle specific tool types
- Add custom error handling for tool calls
- Implement tool-specific response formatting
2. **Response Processing**
- Customize how tool results are formatted
- Add response filtering or transformation
- Implement custom logging
3. **User Interface**
- Add a GUI or web interface
- Implement rich console output
- Add command history or auto-completion
## Running the Client
To run your client with any MCP server:
```bash
python client.py path/to/server.py
uv run client.py path/to/server.py # python server
uv run client.py path/to/build/index.js # node server
```
The client will:
@ -236,6 +313,12 @@ The client will:
- See tool executions
- Get responses from Claude
Here's an example of what it should look like if connected to the weather server from the quickstart:
<Frame>
<img src="/images/client-claude-cli-python.png" />
</Frame>
## How It Works
When you submit a query:
@ -248,7 +331,7 @@ When you submit a query:
6. Claude provides a natural language response
7. The response is displayed to you
## Best Practices
## Best practices
1. **Error Handling**
- Always wrap tool calls in try-catch blocks
@ -265,17 +348,532 @@ When you submit a query:
- Validate server responses
- Be cautious with tool permissions
## Next Steps
## Troubleshooting
Now that you have a basic MCP client, you can:
1. Add support for different server types
2. Enhance error handling and recovery
3. Implement more sophisticated conversation handling
4. Add authentication and security features
5. Create a better user interface
### Server Path Issues
- Double-check the path to your server script is correct
- Use the absolute path if the relative path isn't working
- For Windows users, make sure to use forward slashes (/) or escaped backslashes (\\) in the path
- Verify the server file has the correct extension (.py for Python or .js for Node.js)
## Resources
Example of correct path usage:
```bash
# Relative path
uv run client.py ./server/weather.py
- [MCP Documentation](https://modelcontextprotocol.github.io/)
- [Claude API Documentation](https://docs.anthropic.com/claude/reference)
- [Tool Use Guide](https://docs.anthropic.com/claude/docs/function-calling)
# Absolute path
uv run client.py /Users/username/projects/mcp-server/weather.py
# Windows path (either format works)
uv run client.py C:/projects/mcp-server/weather.py
uv run client.py C:\\projects\\mcp-server\\weather.py
```
### Response Timing
- The first response might take up to 30 seconds to return
- This is normal and happens while:
- The server initializes
- Claude processes the query
- Tools are being executed
- Subsequent responses are typically faster
- Don't interrupt the process during this initial waiting period
### Common Error Messages
If you see:
- `FileNotFoundError`: Check your server path
- `Connection refused`: Ensure the server is running and the path is correct
- `Tool execution failed`: Verify the tool's required environment variables are set
- `Timeout error`: Consider increasing the timeout in your client configuration
</Tab>
<Tab title="Node">
## System Requirements
Before starting, ensure your system meets these requirements:
- Mac or Windows computer
- Node.js version 16 or higher installed
- npm (comes with Node.js)
## Setting Up Your Environment
First, create a new Node.js project:
```bash
# Create project directory
mkdir mcp-client
cd mcp-client
# Initialize npm project
npm init -y
# Install dependencies
npm install @modelcontextprotocol/sdk @anthropic-ai/sdk dotenv
npm install -D typescript @types/node
# Create TypeScript config
npx tsc --init
# Create necessary files
mkdir src
touch src/client.ts
touch .env
```
Update your `package.json` to add necessary configuration:
```json
{
"type": "module",
"scripts": {
"build": "tsc",
"start": "node build/client.js"
}
}
```
Update your `tsconfig.json` with appropriate settings:
```json
{
"compilerOptions": {
"target": "ES2022",
"module": "Node16",
"moduleResolution": "Node16",
"outDir": "./build",
"rootDir": "./src",
"strict": true,
"esModuleInterop": true,
"skipLibCheck": true,
"forceConsistentCasingInFileNames": true
},
"include": ["src/**/*"]
}
```
## Setting Up Your API Key
You'll need an Anthropic API key from the [Anthropic Console](https://console.anthropic.com/settings/keys).
Create a `.env` file:
```bash
ANTHROPIC_API_KEY=your_key_here
```
Add `.env` to your `.gitignore`:
```bash
echo ".env" >> .gitignore
```
## Creating the Client
First, let's set up our imports and create the basic client class in `src/client.ts`:
```typescript
import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
import Anthropic from "@anthropic-ai/sdk";
import dotenv from "dotenv";
import { Tool } from "@anthropic-ai/sdk/resources/messages.js";
import {
CallToolResultSchema,
ListToolsResultSchema,
} from "@modelcontextprotocol/sdk/types.js";
import * as readline from "node:readline";
dotenv.config();
interface MCPClientConfig {
name?: string;
version?: string;
}
class MCPClient {
private client: Client | null = null;
private anthropic: Anthropic;
private transport: StdioClientTransport | null = null;
constructor(config: MCPClientConfig = {}) {
this.anthropic = new Anthropic();
}
// Methods will go here
}
```
## Server Connection Management
Next, implement the method to connect to an MCP server:
```typescript
async connectToServer(serverScriptPath: string): Promise<void> {
const isPython = serverScriptPath.endsWith(".py");
const isJs = serverScriptPath.endsWith(".js");
if (!isPython && !isJs) {
throw new Error("Server script must be a .py or .js file");
}
const command = isPython ? "python" : "node";
this.transport = new StdioClientTransport({
command,
args: [serverScriptPath],
});
this.client = new Client(
{
name: "mcp-client",
version: "1.0.0",
},
{
capabilities: {},
}
);
await this.client.connect(this.transport);
// List available tools
const response = await this.client.request(
{ method: "tools/list" },
ListToolsResultSchema
);
console.log(
"\nConnected to server with tools:",
response.tools.map((tool: any) => tool.name)
);
}
```
## Query Processing Logic
Now add the core functionality for processing queries and handling tool calls:
```typescript
async processQuery(query: string): Promise<string> {
if (!this.client) {
throw new Error("Client not connected");
}
// Initialize messages array with user query
let messages: Anthropic.MessageParam[] = [
{
role: "user",
content: query,
},
];
// Get available tools
const toolsResponse = await this.client.request(
{ method: "tools/list" },
ListToolsResultSchema
);
const availableTools: Tool[] = toolsResponse.tools.map((tool: any) => ({
name: tool.name,
description: tool.description,
input_schema: tool.inputSchema,
}));
const finalText: string[] = [];
let currentResponse = await this.anthropic.messages.create({
model: "claude-3-5-sonnet-20241022",
max_tokens: 1000,
messages,
tools: availableTools,
});
// Process the response and any tool calls
while (true) {
// Add Claude's response to final text and messages
for (const content of currentResponse.content) {
if (content.type === "text") {
finalText.push(content.text);
} else if (content.type === "tool_use") {
const toolName = content.name;
const toolArgs = content.input;
// Execute tool call
const result = await this.client.request(
{
method: "tools/call",
params: {
name: toolName,
args: toolArgs,
},
},
CallToolResultSchema
);
finalText.push(
`[Calling tool ${toolName} with args ${JSON.stringify(toolArgs)}]`
);
// Add Claude's response (including tool use) to messages
messages.push({
role: "assistant",
content: currentResponse.content,
});
// Add tool result to messages
messages.push({
role: "user",
content: [
{
type: "tool_result",
tool_use_id: content.id,
content: [
{ type: "text", text: JSON.stringify(result.content) },
],
},
],
});
// Get next response from Claude with tool results
currentResponse = await this.anthropic.messages.create({
model: "claude-3-5-sonnet-20241022",
max_tokens: 1000,
messages,
tools: availableTools,
});
// Add Claude's interpretation of the tool results to final text
if (currentResponse.content[0]?.type === "text") {
finalText.push(currentResponse.content[0].text);
}
// Continue the loop to process any additional tool calls
continue;
}
}
// If we reach here, there were no tool calls in the response
break;
}
return finalText.join("\n");
}
```
## Interactive Chat Interface
Add the chat loop and cleanup functionality:
```typescript
async chatLoop(): Promise<void> {
console.log("\nMCP Client Started!");
console.log("Type your queries or 'quit' to exit.");
// Using Node's readline for console input
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout,
});
const askQuestion = () => {
rl.question("\nQuery: ", async (query: string) => {
try {
if (query.toLowerCase() === "quit") {
await this.cleanup();
rl.close();
return;
}
const response = await this.processQuery(query);
console.log("\n" + response);
askQuestion();
} catch (error) {
console.error("\nError:", error);
askQuestion();
}
});
};
askQuestion();
}
async cleanup(): Promise<void> {
if (this.transport) {
await this.transport.close();
}
}
```
## Main Entry Point
Finally, add the main execution logic outside the class:
```typescript
// Main execution
async function main() {
if (process.argv.length < 3) {
console.log("Usage: ts-node client.ts <path_to_server_script>");
process.exit(1);
}
const client = new MCPClient();
try {
await client.connectToServer(process.argv[2]);
await client.chatLoop();
} catch (error) {
console.error("Error:", error);
await client.cleanup();
process.exit(1);
}
}
// Run main if this is the main module
if (import.meta.url === new URL(process.argv[1], "file:").href) {
main();
}
export default MCPClient;
```
## Running the Client
To run your client with any MCP server:
```bash
# Build the TypeScript code. Make sure to rerun this every time you update `client.ts`!
npm run build
# Run the client
node build/client.js path/to/server.py # for Python servers
node build/client.js path/to/server.js # for Node.js servers
```
The client will:
1. Connect to the specified server
2. List available tools
3. Start an interactive chat session where you can:
- Enter queries
- See tool executions
- Get responses from Claude
## Key Components Explained
#### 1. Client Initialization
- The `MCPClient` class initializes with session management and API clients
- Sets up the MCP client with basic capabilities
- Configures the Anthropic client for Claude interactions
#### 2. Server Connection
- Supports both Python and Node.js servers
- Validates server script type
- Sets up proper communication channels
- Lists available tools on connection
#### 3. Query Processing
- Maintains conversation context
- Handles Claude's responses and tool calls
- Manages the message flow between Claude and tools
- Combines results into a coherent response
#### 4. Interactive Interface
- Provides a simple command-line interface
- Handles user input and displays responses
- Includes basic error handling
- Allows graceful exit
#### 5. Resource Management
- Proper cleanup of resources
- Error handling for connection issues
- Graceful shutdown procedures
### Common Customization Points
1. **Tool Handling**
- Modify `processQuery()` to handle specific tool types
- Add custom error handling for tool calls
- Implement tool-specific response formatting
2. **Response Processing**
- Customize how tool results are formatted
- Add response filtering or transformation
- Implement custom logging
3. **User Interface**
- Add a GUI or web interface
- Implement rich console output
- Add command history or auto-completion
### Best Practices
1. **Error Handling**
- Always wrap tool calls in try-catch blocks
- Provide meaningful error messages
- Gracefully handle connection issues
2. **Resource Management**
- Use proper cleanup methods
- Close connections when done
- Handle server disconnections
3. **Security**
- Store API keys securely in `.env`
- Validate server responses
- Be cautious with tool permissions
### Troubleshooting
#### Server Path Issues
- Double-check the path to your server script
- Use absolute paths if relative paths aren't working
- For Windows users, use forward slashes (/) or escaped backslashes (\\)
- Verify the server file has the correct extension (.py or .js)
Example of correct path usage:
```bash
# Relative path
node build/client.js ./server/weather.js
# Absolute path
node build/client.js /Users/username/projects/mcp-server/weather.js
# Windows path (either format works)
node build/client.js C:/projects/mcp-server/weather.js
node build/client.js C:\\projects\\mcp-server\\weather.js
```
#### Connection Issues
- Verify the server script exists and has correct permissions
- Check that the server script is executable
- Ensure the server script's dependencies are installed
- Try running the server script directly to check for errors
#### Tool Execution Issues
- Check server logs for error messages
- Verify tool input arguments match the schema
- Ensure tool dependencies are available
- Add debug logging to track execution flow
</Tab>
</Tabs>
## Next steps
<CardGroup cols={1}>
<Card
title="Building a local fileserver"
icon="files"
href="/examples"
>
Build an intermediate MCP server that communicates with your local filesystem
</Card>
<Card
title="Example servers"
icon="grid"
href="/examples"
>
Check out our gallery of official MCP servers and implementations
</Card>
<Card
title="Core architecture"
icon="sitemap"
href="/docs/concepts/architecture"
>
Understand how MCP connects clients, servers, and LLMs
</Card>
</CardGroup>