MCP Server Types: Deep Dive

Complete reference for all MCP server types supported in Claude Code plugins.

stdio (Standard Input/Output)

Overview

Execute local MCP servers as child processes with communication via stdin/stdout. Best choice for local tools, custom servers, and NPM packages.

Configuration

Basic:

{
  "my-server": {
    "command": "npx",
    "args": ["-y", "my-mcp-server"]
  }
}

With environment:

{
  "my-server": {
    "command": "${CLAUDE_PLUGIN_ROOT}/servers/custom-server",
    "args": ["--config", "${CLAUDE_PLUGIN_ROOT}/config.json"],
    "env": {
      "API_KEY": "${MY_API_KEY}",
      "LOG_LEVEL": "debug",
      "DATABASE_URL": "${DB_URL}"
    }
  }
}

Process Lifecycle

1. Startup: Claude Code spawns process with command and args
2. Communication: JSON-RPC messages via stdin/stdout
3. Lifecycle: Process runs for entire Claude Code session
4. Shutdown: Process terminated when Claude Code exits

Use Cases

NPM Packages:

{
  "filesystem": {
    "command": "npx",
    "args": ["-y", "@modelcontextprotocol/server-filesystem", "/path"]
  }
}

Custom Scripts:

{
  "custom": {
    "command": "${CLAUDE_PLUGIN_ROOT}/servers/my-server.js",
    "args": ["--verbose"]
  }
}

Python Servers:

{
  "python-server": {
    "command": "python",
    "args": ["-m", "my_mcp_server"],
    "env": {
      "PYTHONUNBUFFERED": "1"
    }
  }
}

Best Practices

1. Use absolute paths or ${CLAUDEPLUGINROOT}
2. Set PYTHONUNBUFFERED for Python servers
3. Pass configuration via args or env, not stdin
4. Handle server crashes gracefully
5. Log to stderr, not stdout (stdout is for MCP protocol)

Troubleshooting

Server won't start:

• Check command exists and is executable
• Verify file paths are correct
• Check permissions
• Review claude --debug logs

Communication fails:

• Ensure server uses stdin/stdout correctly
• Check for stray print/console.log statements
• Verify JSON-RPC format

SSE (Server-Sent Events)

Overview

Connect to hosted MCP servers via HTTP with server-sent events for streaming. Best for cloud services and OAuth authentication.

Configuration

Basic:

{
  "hosted-service": {
    "type": "sse",
    "url": "https://mcp.example.com/sse"
  }
}

With headers:

{
  "service": {
    "type": "sse",
    "url": "https://mcp.example.com/sse",
    "headers": {
      "X-API-Version": "v1",
      "X-Client-ID": "${CLIENT_ID}"
    }
  }
}

Connection Lifecycle

1. Initialization: HTTP connection established to URL
2. Handshake: MCP protocol negotiation
3. Streaming: Server sends events via SSE
4. Requests: Client sends HTTP POST for tool calls
5. Reconnection: Automatic reconnection on disconnect

Authentication

OAuth (Automatic):

{
  "asana": {
    "type": "sse",
    "url": "https://mcp.asana.com/sse"
  }
}

Claude Code handles OAuth flow:

1. User prompted to authenticate on first use
2. Opens browser for OAuth flow
3. Tokens stored securely
4. Automatic token refresh

Custom Headers:

{
  "service": {
    "type": "sse",
    "url": "https://mcp.example.com/sse",
    "headers": {
      "Authorization": "Bearer ${API_TOKEN}"
    }
  }
}

Use Cases

Official Services:

• Asana: https://mcp.asana.com/sse
• GitHub: https://mcp.github.com/sse
• Other hosted MCP servers

Custom Hosted Servers: Deploy your own MCP server and expose via HTTPS + SSE.

Best Practices

1. Always use HTTPS, never HTTP
2. Let OAuth handle authentication when available
3. Use environment variables for tokens
4. Handle connection failures gracefully
5. Document OAuth scopes required

Troubleshooting

Connection refused:

• Check URL is correct and accessible
• Verify HTTPS certificate is valid
• Check network connectivity
• Review firewall settings

OAuth fails:

• Clear cached tokens
• Check OAuth scopes
• Verify redirect URLs
• Re-authenticate

HTTP (REST API)

Overview

Connect to RESTful MCP servers via standard HTTP requests. Best for token-based auth and stateless interactions.

Configuration

Basic:

{
  "api": {
    "type": "http",
    "url": "https://api.example.com/mcp"
  }
}

With authentication:

{
  "api": {
    "type": "http",
    "url": "https://api.example.com/mcp",
    "headers": {
      "Authorization": "Bearer ${API_TOKEN}",
      "Content-Type": "application/json",
      "X-API-Version": "2024-01-01"
    }
  }
}

Request/Response Flow

1. Tool Discovery: GET to discover available tools
2. Tool Invocation: POST with tool name and parameters
3. Response: JSON response with results or errors
4. Stateless: Each request independent

Authentication

Token-Based:

{
  "headers": {
    "Authorization": "Bearer ${API_TOKEN}"
  }
}

API Key:

{
  "headers": {
    "X-API-Key": "${API_KEY}"
  }
}

Custom Auth:

{
  "headers": {
    "X-Auth-Token": "${AUTH_TOKEN}",
    "X-User-ID": "${USER_ID}"
  }
}

Use Cases

• REST API backends
• Internal services
• Microservices
• Serverless functions

Best Practices

1. Use HTTPS for all connections
2. Store tokens in environment variables
3. Implement retry logic for transient failures
4. Handle rate limiting
5. Set appropriate timeouts

Troubleshooting

HTTP errors:

• 401: Check authentication headers
• 403: Verify permissions
• 429: Implement rate limiting
• 500: Check server logs

Timeout issues:

• Increase timeout if needed
• Check server performance
• Optimize tool implementations

WebSocket (Real-time)

Overview

Connect to MCP servers via WebSocket for real-time bidirectional communication. Best for streaming and low-latency applications.

Configuration

Basic:

{
  "realtime": {
    "type": "ws",
    "url": "wss://mcp.example.com/ws"
  }
}

With authentication:

{
  "realtime": {
    "type": "ws",
    "url": "wss://mcp.example.com/ws",
    "headers": {
      "Authorization": "Bearer ${TOKEN}",
      "X-Client-ID": "${CLIENT_ID}"
    }
  }
}

Connection Lifecycle

1. Handshake: WebSocket upgrade request
2. Connection: Persistent bidirectional channel
3. Messages: JSON-RPC over WebSocket
4. Heartbeat: Keep-alive messages
5. Reconnection: Automatic on disconnect

Use Cases

• Real-time data streaming
• Live updates and notifications
• Collaborative editing
• Low-latency tool calls
• Push notifications from server

Best Practices

1. Use WSS (secure WebSocket), never WS
2. Implement heartbeat/ping-pong
3. Handle reconnection logic
4. Buffer messages during disconnection
5. Set connection timeouts

Troubleshooting

Connection drops:

• Implement reconnection logic
• Check network stability
• Verify server supports WebSocket
• Review firewall settings

Message delivery:

• Implement message acknowledgment
• Handle out-of-order messages
• Buffer during disconnection

Comparison Matrix

Choosing the Right Type

Use stdio when:

• Running local tools or custom servers
• Need lowest latency
• Working with file systems or local databases
• Distributing server with plugin

Use SSE when:

• Connecting to hosted services
• Need OAuth authentication
• Using official MCP servers (Asana, GitHub)
• Want automatic reconnection

Use HTTP when:

• Integrating with REST APIs
• Need stateless interactions
• Using token-based auth
• Simple request/response pattern

Use WebSocket when:

• Need real-time updates
• Building collaborative features
• Low-latency critical
• Bi-directional streaming required

Migration Between Types

From stdio to SSE

Before (stdio):

{
  "local-server": {
    "command": "node",
    "args": ["server.js"]
  }
}

After (SSE - deploy server):

{
  "hosted-server": {
    "type": "sse",
    "url": "https://mcp.example.com/sse"
  }
}

From HTTP to WebSocket

Before (HTTP):

{
  "api": {
    "type": "http",
    "url": "https://api.example.com/mcp"
  }
}

After (WebSocket):

{
  "realtime": {
    "type": "ws",
    "url": "wss://api.example.com/ws"
  }
}

Benefits: Real-time updates, lower latency, bi-directional communication.

Advanced Configuration

Multiple Servers

Combine different types:

{
  "local-db": {
    "command": "npx",
    "args": ["-y", "mcp-server-sqlite", "./data.db"]
  },
  "cloud-api": {
    "type": "sse",
    "url": "https://mcp.example.com/sse"
  },
  "internal-service": {
    "type": "http",
    "url": "https://api.example.com/mcp",
    "headers": {
      "Authorization": "Bearer ${API_TOKEN}"
    }
  }
}

Conditional Configuration

Use environment variables to switch servers:

{
  "api": {
    "type": "http",
    "url": "${API_URL}",
    "headers": {
      "Authorization": "Bearer ${API_TOKEN}"
    }
  }
}

Set different values for dev/prod:

• Dev: API_URL=http://localhost:8080/mcp
• Prod: API_URL=https://api.production.com/mcp

Security Considerations

Stdio Security

• Validate command paths
• Don't execute user-provided commands
• Limit environment variable access
• Restrict file system access

Network Security

• Always use HTTPS/WSS
• Validate SSL certificates
• Don't skip certificate verification
• Use secure token storage

Token Management

• Never hardcode tokens
• Use environment variables
• Rotate tokens regularly
• Implement token refresh
• Document scopes required

Conclusion

Choose the MCP server type based on your use case:

• stdio for local, custom, or NPM-packaged servers
• SSE for hosted services with OAuth
• HTTP for REST APIs with token auth
• WebSocket for real-time bidirectional communication

Test thoroughly and handle errors gracefully for robust MCP integration.