---
title: "MCP Servers"
description: "Understanding MCP servers and how to create, configure, and use them with mcp-agent."
---

import { Card, CardGroup } from "@mintlify/components";

## What are MCP Servers?

**MCP Servers** are the powerhouse behind agents in the `mcp-agent` framework. They provide specialized capabilities to agents through the Model Context Protocol (MCP), acting as external tools, data sources, and services that agents can access.

Think of MCP servers as:

- **Tools** that agents can call to perform specific tasks
- **Data sources** that provide access to information and resources
- **Services** that extend agent capabilities beyond the base LLM
- **Independent processes** that can be developed, deployed, and scaled separately

<Card>
  **Core Concept:** MCP Servers extend agent capabilities by providing tools,
  resources, and prompts through a standardized protocol.
</Card>

## Server Types and Transports

The `mcp-agent` framework supports multiple transport mechanisms for connecting to MCP servers:

### STDIO (Standard Input/Output)

Best for local development and subprocess-based servers:

```yaml
# mcp_agent.config.yaml
mcp:
  servers:
    filesystem:
      transport: "stdio" # Default transport
      command: "npx"
      args: ["-y", "@modelcontextprotocol/server-filesystem"]
      env:  # Environment variables passed to the server process
        ROOT_PATH: "/path/to/files"
      terminate_on_close: true # Default: true
```

### Server-Sent Events (SSE)

Ideal for streaming responses and real-time data:

```yaml
mcp:
  servers:
    sse_server:
      transport: "sse"
      url: "http://localhost:8000/sse"
      headers:
        Authorization: "Bearer your-token"
      http_timeout_seconds: 30
      read_timeout_seconds: 60
```

### WebSocket

For bidirectional, persistent connections:

```yaml
mcp:
  servers:
    websocket_server:
      transport: "websocket"
      url: "ws://localhost:8001/ws"
      headers:
        Authorization: "Bearer your-token"
```

### Streamable HTTP

For HTTP-based servers with streaming support:

```yaml
mcp:
  servers:
    http_server:
      transport: "streamable_http"
      url: "http://localhost:8002/mcp"
      headers:
        Authorization: "Bearer your-token"
        Content-Type: "application/json"
      http_timeout_seconds: 30
      read_timeout_seconds: 120
```

## Server Capabilities

MCP servers can provide three main types of capabilities:

### 1. Tools

Functions that agents can call to perform actions:

```python
# Example tool implementation using FastMCP
from mcp.server.fastmcp import FastMCP

mcp = FastMCP("My Server")

@mcp.tool()
def calculate_sum(a: int, b: int) -> int:
    """Calculate the sum of two numbers."""
    return a + b

@mcp.tool()
def fetch_weather(city: str) -> str:
    """Get weather information for a city."""
    # Implementation here
    return f"Weather in {city}: Sunny, 75°F"
```

### 2. Resources

Data and content that agents can read and reference:

```python
@mcp.resource("file://{path}")
def read_file(path: str) -> str:
    """Read content from a file."""
    with open(path, 'r') as f:
        return f.read()

@mcp.resource("db://users/{user_id}")
def get_user(user_id: str) -> dict:
    """Get user information from database."""
    # Database lookup implementation
    return {"id": user_id, "name": "John Doe"}
```

### 3. Prompts

Reusable prompt templates that agents can utilize:

```python
@mcp.prompt()
def analysis_prompt(data: str, context: str = "") -> str:
    """Generate an analysis prompt with data and optional context."""
    return f"""Analyze the following data:

Data: {data}
Context: {context}

Provide a detailed analysis including key insights and recommendations."""
```

## Configuration Examples

### Basic Server Configuration

```yaml
# mcp_agent.config.yaml
$schema: ../../schema/mcp-agent.config.schema.json

execution_engine: asyncio

mcp:
  servers:
    # Filesystem access
    filesystem:
      command: "npx"
      args: ["-y", "@modelcontextprotocol/server-filesystem"]
      env:  # Environment variables passed to the server process
        ROOT_PATH: "/workspace"

    # Web fetching capabilities
    fetch:
      command: "uvx"
      args: ["mcp-server-fetch"]

    # Custom SSE server
    analytics:
      url: "http://localhost:8000/sse"
      transport: "sse"
      headers:
        Authorization: "Bearer ${ANALYTICS_TOKEN}"
```

### Advanced Server Configuration

```yaml
mcp:
  servers:
    # Production database server with authentication
    database:
      name: "Production Database Server"
      description: "Provides access to production database"
      transport: "streamable_http"
      url: "https://api.example.com/mcp"
      headers:
        Authorization: "Bearer ${DB_API_TOKEN}"
        X-Client-ID: "${CLIENT_ID}"
      http_timeout_seconds: 30
      read_timeout_seconds: 120
      auth:
        type: "bearer"
        token: "${DB_API_TOKEN}"

    # Local development server with custom environment and roots
    dev_tools:
      name: "Development Tools Server"
      description: "Local development tools and utilities"
      transport: "stdio"
      command: "python"
      args: ["-m", "my_mcp_server"]
      env:  # Environment variables passed to the server process
        DEBUG: "true"
        LOG_LEVEL: "debug"
        DATABASE_URL: "${DEV_DATABASE_URL}"
      terminate_on_close: true
      roots:
        - uri: "file:///workspace"
          name: "Workspace"
        - uri: "file:///tmp"
          name: "Temporary Files"
```

## Creating Your Own MCP Server

### Using FastMCP (Recommended)

FastMCP provides the easiest way to create MCP servers:

```python
# server.py
from mcp.server.fastmcp import FastMCP
from mcp.server.models import InitializationOptions
import asyncio

# Create the server
mcp = FastMCP("My Custom Server")

@mcp.tool()
def greet(name: str) -> str:
    """Greet someone by name."""
    return f"Hello, {name}! Nice to meet you."

@mcp.tool()
async def async_calculation(x: float, y: float) -> float:
    """Perform an async calculation."""
    await asyncio.sleep(0.1)  # Simulate async work
    return x * y + 42

@mcp.resource("data://{dataset}")
def get_dataset(dataset: str) -> str:
    """Get dataset information."""
    datasets = {
        "sales": "Q1 Sales: $1.2M, Q2 Sales: $1.5M",
        "users": "Active Users: 15,432, New Users: 1,234"
    }
    return datasets.get(dataset, "Dataset not found")

@mcp.prompt()
def report_prompt(data_type: str, period: str = "monthly") -> str:
    """Generate a report prompt template."""
    return f"""Please create a {period} report for {data_type}.

Include:
1. Summary of key metrics
2. Trends and patterns
3. Recommendations for improvement
4. Action items for next period

Format the report in a clear, professional manner."""

# Run the server
if __name__ == "__main__":
    mcp.run()
```

## Integration Patterns

### Using Servers with Agents

```python
from mcp_agent.agents.agent import Agent
from mcp_agent.workflows.llm.augmented_llm_openai import OpenAIAugmentedLLM

# Create an agent with multiple server types
agent = Agent(
    name="data_analyst",
    instruction="""You are a data analyst with access to databases,
    file systems, and analytics tools. Help users analyze data and
    generate insights.""",
    server_names=["filesystem", "database", "analytics"]
)

async with agent:
    # Discover available tools
    tools = await agent.list_tools()
    print(f"Available tools: {[tool.name for tool in tools.tools]}")

    # Use the agent with an LLM
    llm = await agent.attach_llm(OpenAIAugmentedLLM)

    result = await llm.generate_str(
        "Analyze the sales data from Q1 and create a summary report"
    )
    print(result)
```

## Server Development Best Practices

### 1. Error Handling

```python
@mcp.tool()
def safe_division(a: float, b: float) -> str:
    """Safely divide two numbers."""
    try:
        if b == 0:
            return "Error: Division by zero is not allowed"
        result = a / b
        return f"Result: {result}"
    except Exception as e:
        return f"Error: {str(e)}"
```

### 2. Input Validation

```python
from pydantic import BaseModel, validator

class WeatherRequest(BaseModel):
    city: str
    units: str = "fahrenheit"

    @validator('city')
    def city_must_not_be_empty(cls, v):
        if not v.strip():
            raise ValueError('City name cannot be empty')
        return v.strip()

    @validator('units')
    def units_must_be_valid(cls, v):
        if v not in ['fahrenheit', 'celsius']:
            raise ValueError('Units must be fahrenheit or celsius')
        return v

@mcp.tool()
def get_weather(request: WeatherRequest) -> str:
    """Get weather with validated input."""
    # Implementation here
    return f"Weather in {request.city}: 75°{request.units[0].upper()}"
```

### 3. Async Operations

```python
import aiohttp

@mcp.tool()
async def fetch_url(url: str) -> str:
    """Fetch content from a URL asynchronously."""
    async with aiohttp.ClientSession() as session:
        try:
            async with session.get(url) as response:
                if response.status == 200:
                    content = await response.text()
                    return f"Content fetched successfully (length: {len(content)})"
                else:
                    return f"Error: HTTP {response.status}"
        except Exception as e:
            return f"Error fetching URL: {str(e)}"
```

## Advanced Features

### Elicitation Support

Elicitation allows servers to request additional structured input from users during tool execution:

```python
from mcp.server.fastmcp import FastMCP, Context
from mcp.server.elicitation import (
    AcceptedElicitation,
    DeclinedElicitation,
    CancelledElicitation,
)
from pydantic import BaseModel, Field

mcp = FastMCP("Booking System")

@mcp.tool()
async def book_table(date: str, party_size: int, ctx: Context) -> str:
    """Book a table with confirmation"""
    
    # Schema must only contain primitive types (str, int, float, bool)
    class ConfirmBooking(BaseModel):
        confirm: bool = Field(description="Confirm booking?")
        notes: str = Field(default="", description="Special requests")
    
    result = await ctx.elicit(
        message=f"Confirm booking for {party_size} on {date}?", 
        schema=ConfirmBooking
    )
    
    match result:
        case AcceptedElicitation(data=data):
            if data.confirm:
                return f"Booked! Notes: {data.notes or 'None'}"
            return "Booking cancelled"
        case DeclinedElicitation():
            return "Booking declined"
        case CancelledElicitation():
            return "Booking cancelled"
```

## Production Considerations

### Security

```python
# Use environment variables for sensitive data
import os

@mcp.tool()
def secure_api_call(endpoint: str) -> str:
    """Make a secure API call using stored credentials."""
    api_key = os.getenv("API_KEY")
    if not api_key:
        return "Error: API key not configured"

    # Make authenticated request
    # Implementation here
    return "API call completed successfully"
```

### Performance

```yaml
# Configure timeouts and headers for better performance
mcp:
  servers:
    high_traffic_server:
      transport: "streamable_http"
      url: "https://api.example.com/mcp"
      http_timeout_seconds: 30
      read_timeout_seconds: 120
      headers:
        Keep-Alive: "timeout=60, max=100"
        Connection: "keep-alive"
```

### Monitoring

```python
import logging

# Configure logging in your server
logging.basicConfig(level=logging.INFO)
logger = logging.getLogger(__name__)

@mcp.tool()
def monitored_operation(data: str) -> str:
    """Operation with monitoring and logging."""
    logger.info(f"Starting operation with data length: {len(data)}")

    try:
        # Process data
        result = process_data(data)
        logger.info("Operation completed successfully")
        return result
    except Exception as e:
        logger.error(f"Operation failed: {str(e)}")
        return f"Error: {str(e)}"
```

<CardGroup>
  <Card
    title="Getting Started"
    href="https://github.com/lastmile-ai/mcp-agent/tree/main/examples/mcp"
  >
    Explore example MCP servers and learn implementation patterns.
  </Card>
  <Card
    title="FastMCP Documentation"
    href="https://github.com/modelcontextprotocol/servers"
  >
    Learn more about FastMCP and the official MCP server toolkit.
  </Card>
  <Card title="Agent Integration" href="/concepts/agents">
    Learn how agents discover and use MCP server capabilities.
  </Card>
</CardGroup>
