Model Context Protocol (MCP) enables Claude Code plugins to integrate with external services and APIs by providing structured tool access. Use MCP integration to expose external service capabilities as tools within Claude Code.

Key capabilities:

• Connect to external services (databases, APIs, file systems)
• Provide 10+ related tools from a single service
• Handle OAuth and complex authentication flows
• Bundle MCP servers with plugins for automatic setup

Plugins can bundle MCP servers in two ways:

Create .mcp.json at plugin root:

{
  "database-tools": {
    "command": "${CLAUDE_PLUGIN_ROOT}/servers/db-server",
    "args": ["--config", "${CLAUDE_PLUGIN_ROOT}/config.json"],
    "env": {
      "DB_URL": "${DB_URL}"
    }
  }
}

Benefits:

• Clear separation of concerns
• Easier to maintain
• Better for multiple servers

Add mcpServers field to plugin.json:

{
  "name": "my-plugin",
  "version": "1.0.0",
  "mcpServers": {
    "plugin-api": {
      "command": "${CLAUDE_PLUGIN_ROOT}/servers/api-server",
      "args": ["--port", "8080"]
    }
  }
}

Benefits:

• Single configuration file
• Good for simple single-server plugins

Execute local MCP servers as child processes. Best for local tools and custom servers.

Configuration:

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

Use cases:

• File system access
• Local database connections
• Custom MCP servers
• NPM-packaged MCP servers

Process management:

• Claude Code spawns and manages the process
• Communicates via stdin/stdout
• Terminates when Claude Code exits

Connect to hosted MCP servers with OAuth support. Best for cloud services.

Configuration:

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

Use cases:

• Official hosted MCP servers (Asana, GitHub, etc.)
• Cloud services with MCP endpoints
• OAuth-based authentication
• No local installation needed

Authentication:

• OAuth flows handled automatically
• User prompted on first use
• Tokens managed by Claude Code

Connect to RESTful MCP servers with token authentication.

Configuration:

{
  "api-service": {
    "type": "http",
    "url": "https://api.example.com/mcp",
    "headers": {
      "Authorization": "Bearer ${API_TOKEN}",
      "X-Custom-Header": "value"
    }
  }
}

Use cases:

• REST API-based MCP servers
• Token-based authentication
• Custom API backends
• Stateless interactions

Connect to WebSocket MCP servers for real-time bidirectional communication.

Configuration:

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

Use cases:

• Real-time data streaming
• Persistent connections
• Push notifications from server
• Low-latency requirements

All MCP configurations support environment variable substitution:

${CLAUDE_PLUGIN_ROOT} - Plugin directory (always use for portability):

{
  "command": "${CLAUDE_PLUGIN_ROOT}/servers/my-server"
}

User environment variables - From user's shell:

{
  "env": {
    "API_KEY": "${MY_API_KEY}",
    "DATABASE_URL": "${DB_URL}"
  }
}

Best practice: Document all required environment variables in plugin README.

When MCP servers provide tools, they're automatically prefixed:

Format: mcp__plugin_<plugin-name>_<server-name>__<tool-name>

Example:

• Plugin: asana
• Server: asana
• Tool: create_task
• Full name: mcp__plugin_asana_asana__asana_create_task

Pre-allow specific MCP tools in command frontmatter:

---
allowed-tools: [
  "mcp__plugin_asana_asana__asana_create_task",
  "mcp__plugin_asana_asana__asana_search_tasks"
]
---

Wildcard (use sparingly):

---
allowed-tools: ["mcp__plugin_asana_asana__*"]
---

Best practice: Pre-allow specific tools, not wildcards, for security.

Automatic startup:

• MCP servers start when plugin enables
• Connection established before first tool use
• Restart required for configuration changes

Lifecycle:

1. Plugin loads
2. MCP configuration parsed
3. Server process started (stdio) or connection established (SSE/HTTP/WS)
4. Tools discovered and registered
5. Tools available as mcp__plugin_...__...

Viewing servers: Use /mcp command to see all servers including plugin-provided ones.

OAuth handled automatically by Claude Code:

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

User authenticates in browser on first use. No additional configuration needed.

Static or environment variable tokens:

{
  "type": "http",
  "url": "https://api.example.com",
  "headers": {
    "Authorization": "Bearer ${API_TOKEN}"
  }
}

Document required environment variables in README.

Pass configuration to MCP server:

{
  "command": "python",
  "args": ["-m", "my_mcp_server"],
  "env": {
    "DATABASE_URL": "${DB_URL}",
    "API_KEY": "${API_KEY}",
    "LOG_LEVEL": "info"
  }
}

Commands use MCP tools with user interaction:

# Command: create-item.md
---
allowed-tools: ["mcp__plugin_name_server__create_item"]
---

Steps:
1. Gather item details from user
2. Use mcp__plugin_name_server__create_item
3. Confirm creation

Use for: Adding validation or preprocessing before MCP calls.

Agents use MCP tools autonomously:

# Agent: data-analyzer.md

Analysis Process:
1. Query data via mcp__plugin_db_server__query
2. Process and analyze results
3. Generate insights report

Use for: Multi-step MCP workflows without user interaction.

Integrate multiple MCP servers:

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

Use for: Workflows spanning multiple services.

Always use secure connections:

✅ "url": "https://mcp.example.com/sse"
❌ "url": "http://mcp.example.com/sse"

DO:

• ✅ Use environment variables for tokens
• ✅ Document required env vars in README
• ✅ Let OAuth flow handle authentication

DON'T:

• ❌ Hardcode tokens in configuration
• ❌ Commit tokens to git
• ❌ Share tokens in documentation

Pre-allow only necessary MCP tools:

✅ allowed-tools: [
  "mcp__plugin_api_server__read_data",
  "mcp__plugin_api_server__create_item"
]

❌ allowed-tools: ["mcp__plugin_api_server__*"]

Handle MCP server unavailability:

• Provide fallback behavior in commands
• Inform user of connection issues
• Check server URL and configuration

Handle failed MCP operations:

• Validate inputs before calling MCP tools
• Provide clear error messages
• Check rate limiting and quotas

Validate MCP configuration:

• Test server connectivity during development
• Validate JSON syntax
• Check required environment variables

MCP servers connect on-demand:

• Not all servers connect at startup
• First tool use triggers connection
• Connection pooling managed automatically

Batch similar requests when possible:

# Good: Single query with filters
tasks = search_tasks(project="X", assignee="me", limit=50)

# Avoid: Many individual queries
for id in task_ids:
    task = get_task(id)

1. Configure MCP server in .mcp.json
2. Install plugin locally (.claude-plugin/)
3. Run /mcp to verify server appears
4. Test tool calls in commands
5. Check claude --debug logs for connection issues

• MCP configuration is valid JSON
• Server URL is correct and accessible
• Required environment variables documented
• Tools appear in /mcp output
• Authentication works (OAuth or tokens)
• Tool calls succeed from commands
• Error cases handled gracefully

claude --debug

Look for:

• MCP server connection attempts
• Tool discovery logs
• Authentication flows
• Tool call errors

Server not connecting:

• Check URL is correct
• Verify server is running (stdio)
• Check network connectivity
• Review authentication configuration

Tools not available:

• Verify server connected successfully
• Check tool names match exactly
• Run /mcp to see available tools
• Restart Claude Code after config changes

Authentication failing:

• Clear cached auth tokens
• Re-authenticate
• Check token scopes and permissions
• Verify environment variables set

• Server type specified (stdio/SSE/HTTP/ws)
• Type-specific fields complete (command or url)
• Authentication configured
• Environment variables documented
• HTTPS/WSS used (not HTTP/WS)
• ${CLAUDE_PLUGIN_ROOT} used for paths

DO:

• ✅ Use ${CLAUDE_PLUGIN_ROOT} for portable paths
• ✅ Document required environment variables
• ✅ Use secure connections (HTTPS/WSS)
• ✅ Pre-allow specific MCP tools in commands
• ✅ Test MCP integration before publishing
• ✅ Handle connection and tool errors gracefully

DON'T:

• ❌ Hardcode absolute paths
• ❌ Commit credentials to git
• ❌ Use HTTP instead of HTTPS
• ❌ Pre-allow all tools with wildcards
• ❌ Skip error handling
• ❌ Forget to document setup

For detailed information, consult:

• references/server-types.md - Deep dive on each server type
• references/authentication.md - Authentication patterns and OAuth
• references/tool-usage.md - Using MCP tools in commands and agents

Working examples in examples/:

• stdio-server.json - Local stdio MCP server
• sse-server.json - Hosted SSE server with OAuth
• http-server.json - REST API with token auth

• Official MCP Docs: https://modelcontextprotocol.io/
• Claude Code MCP Docs: https://docs.claude.com/en/docs/claude-code/mcp
• MCP SDK: @modelcontextprotocol/sdk
• Testing: Use claude --debug and /mcp command

To add MCP integration to a plugin:

1. Choose MCP server type (stdio, SSE, HTTP, ws)
2. Create .mcp.json at plugin root with configuration
3. Use ${CLAUDE_PLUGIN_ROOT} for all file references
4. Document required environment variables in README
5. Test locally with /mcp command
6. Pre-allow MCP tools in relevant commands
7. Handle authentication (OAuth or tokens)
8. Test error cases (connection failures, auth errors)
9. Document MCP integration in plugin README

Focus on stdio for custom/local servers, SSE for hosted services with OAuth.