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Overview

Server-Sent Events (SSE) provide a standard way for a web server to send updates to a client over a single, long-lived HTTP connection. In the context of MCP, SSE is used for remote servers to stream data (like tool responses) to your CrewAI application in real-time.

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Key Concepts

  • Remote Servers: SSE is suitable for MCP servers hosted remotely.
  • Unidirectional Stream: Typically, SSE is a one-way communication channel from server to client.
  • MCPServerAdapter Configuration: For SSE, you’ll provide the server’s URL and specify the transport type.

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Connecting via SSE

You can connect to an SSE-based MCP server using two main approaches for managing the connection lifecycle:

Using a Python context manager (with statement) is the recommended approach. It automatically handles establishing and closing the connection to the SSE MCP server.

from crewai import Agent, Task, Crew, Process
from crewai_tools import MCPServerAdapter

server_params = {
    "url": "http://localhost:8000/sse", # Replace with your actual SSE server URL
    "transport": "sse" 
}

# Using MCPServerAdapter with a context manager
try:
    with MCPServerAdapter(server_params) as tools:
        print(f"Available tools from SSE MCP server: {[tool.name for tool in tools]}")

        # Example: Using a tool from the SSE MCP server
        sse_agent = Agent(
            role="Remote Service User",
            goal="Utilize a tool provided by a remote SSE MCP server.",
            backstory="An AI agent that connects to external services via SSE.",
            tools=tools,
            reasoning=True,
            verbose=True,
        )

        sse_task = Task(
            description="Fetch real-time stock updates for 'AAPL' using an SSE tool.",
            expected_output="The latest stock price for AAPL.",
            agent=sse_agent,
            markdown=True
        )

        sse_crew = Crew(
            agents=[sse_agent],
            tasks=[sse_task],
            verbose=True,
            process=Process.sequential
        )
        
        if tools: # Only kickoff if tools were loaded
            result = sse_crew.kickoff() # Add inputs={'stock_symbol': 'AAPL'} if tool requires it
            print("\nCrew Task Result (SSE - Managed):\n", result)
        else:
            print("Skipping crew kickoff as tools were not loaded (check server connection).")

except Exception as e:
    print(f"Error connecting to or using SSE MCP server (Managed): {e}")
    print("Ensure the SSE MCP server is running and accessible at the specified URL.")

Replace "http://localhost:8000/sse" with the actual URL of your SSE MCP server.

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2. Manual Connection Lifecycle

If you need finer-grained control, you can manage the MCPServerAdapter connection lifecycle manually.

You MUST call mcp_server_adapter.stop() to ensure the connection is closed and resources are released. Using a try...finally block is highly recommended.

from crewai import Agent, Task, Crew, Process
from crewai_tools import MCPServerAdapter

server_params = {
    "url": "http://localhost:8000/sse", # Replace with your actual SSE server URL
    "transport": "sse"
}

mcp_server_adapter = None 
try:
    mcp_server_adapter = MCPServerAdapter(server_params)
    mcp_server_adapter.start()
    tools = mcp_server_adapter.tools
    print(f"Available tools (manual SSE): {[tool.name for tool in tools]}")

    manual_sse_agent = Agent(
        role="Remote Data Analyst",
        goal="Analyze data fetched from a remote SSE MCP server using manual connection management.",
        backstory="An AI skilled in handling SSE connections explicitly.",
        tools=tools,
        verbose=True
    )
    
    analysis_task = Task(
        description="Fetch and analyze the latest user activity trends from the SSE server.",
        expected_output="A summary report of user activity trends.",
        agent=manual_sse_agent
    )
    
    analysis_crew = Crew(
        agents=[manual_sse_agent],
        tasks=[analysis_task],
        verbose=True,
        process=Process.sequential
    )
    
    result = analysis_crew.kickoff()
    print("\nCrew Task Result (SSE - Manual):\n", result)

except Exception as e:
    print(f"An error occurred during manual SSE MCP integration: {e}")
    print("Ensure the SSE MCP server is running and accessible.")
finally:
    if mcp_server_adapter and mcp_server_adapter.is_connected:
        print("Stopping SSE MCP server connection (manual)...")
        mcp_server_adapter.stop()  # **Crucial: Ensure stop is called**
    elif mcp_server_adapter:
        print("SSE MCP server adapter was not connected. No stop needed or start failed.")

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Security Considerations for SSE

DNS Rebinding Attacks: SSE transports can be vulnerable to DNS rebinding attacks if the MCP server is not properly secured. This could allow malicious websites to interact with local or intranet-based MCP servers.

To mitigate this risk:

  • MCP server implementations should validate Origin headers on incoming SSE connections.
  • When running local SSE MCP servers for development, bind only to localhost (127.0.0.1) rather than all network interfaces (0.0.0.0).
  • Implement proper authentication for all SSE connections if they expose sensitive tools or data.

For a comprehensive overview of security best practices, please refer to our Security Considerations page and the official MCP Transport Security documentation.