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What’s an MCP Server?

MCP servers are specialized extensions that enhance Cline’s capabilities. They enable Cline to perform additional tasks like fetching web pages, processing images, accessing APIs, and much more.

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MCP Marketplace Walkthrough

The MCP Marketplace provides a one-click installation experience for hundreds of MCP servers across various categories.

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1. Access the Marketplace

  • In Cline, click the “Extensions” button (square icon) in the top toolbar
  • The MCP marketplace will open, showing available servers by category

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2. Browse and Select a Server

  • Browse servers by category (Search, File-systems, Browser-automation, Research-data, etc.)
  • Click on a server to see details about its capabilities and requirements

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3. Install and Configure

  • Click the install button for your chosen server
  • If the server requires an API key (most do), Cline will guide you through:
    • Where to get the API key
    • How to enter it securely
  • The server will be added to your MCP settings automatically

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4. Verify Installation

  • Cline will show confirmation when installation is complete
  • Check the server status in Cline’s MCP settings UI

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5. Using Your New Server

  • After successful installation, Cline will automatically integrate the server’s capabilities
  • You’ll see new tools and resources available in Cline’s system prompt
  • Simply ask Cline to use the capabilities of your new server
  • Example: “Search the web for recent React updates using Perplexity”

Corporate Users: If you’re using Cline in a corporate environment, ensure you have permission to install third-party MCP servers according to your organization’s security policies.

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What Happens Behind the Scenes

When you install an MCP server, several things happen automatically:

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1. Installation Process

  • The server code is cloned/installed to /Users/<username>/Documents/Cline/MCP/
  • Dependencies are installed
  • The server is built (TypeScript/JavaScript compilation or Python package installation)

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2. Configuration

  • The MCP settings file is updated with your server configuration
  • This file is located at: /Users/<username>/Library/Application Support/Code/User/globalStorage/saoudrizwan.claude-dev/settings/cline_mcp_settings.json
  • Environment variables (like API keys) are securely stored
  • The server path is registered

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3. Server Launch

  • Cline detects the configuration change
  • Cline launches your server as a separate process
  • Communication is established via stdio or HTTP

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4. Integration with Cline

  • Your server’s capabilities are added to Cline’s system prompt
  • Tools become available via use_mcp_tool commands
  • Resources become available via access_mcp_resource commands
  • Cline can now use these capabilities when prompted by the user

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Troubleshooting

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System Requirements

Make sure your system meets these requirements:

  • Node.js 18.x or newer
    • Check by running: node --version
    • Install from: https://nodejs.org/
    • Required for JavaScript/TypeScript implementations
  • Python 3.10 or newer
    • Check by running: python --version
    • Install from: https://python.org/
    • Note: Some specialized implementations may require Python 3.11+
  • UV Package Manager
    • Modern Python package manager for dependency isolation
    • Install using: 
      curl -LsSf https://astral.sh/uv/install.sh | sh
      Or: pip install uv
    • Verify with: uv --version

If any of these commands fail or show older versions, please install/update before continuing!

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Common Installation Issues

  • Ensure your internet connection is stable
  • Check that you have the necessary permissions to install new software
  • Verify that the API key was entered correctly (if required)
  • Check the server status in the MCP settings UI for any error messages

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How to Remove an MCP Server

To completely remove a faulty MCP server:

  1. Open the MCP settings file: /Users/<username>/Library/Application Support/Code/User/globalStorage/saoudrizwan.claude-dev/settings/cline_mcp_settings.json
  2. Delete the entire entry for your server from the mcpServers object
  3. Save the file
  4. Restart Cline

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I’m Still Getting an Error

If you’re getting an error when using an MCP server, you can try the following:

  • Check the MCP settings file for errors
  • Use a Claude Sonnet model for installation
  • Verify that paths to your server’s files are correct
  • Ensure all required environment variables are set
  • Check if another process is using the same port (for HTTP-based servers)
  • Try removing and reinstalling the server (remove from both the cline_mcp_settings.json file and the /Users/<username>/Documents/Cline/MCP/ directory)
  • Use a terminal and run the command with its arguments directly. This will allow you to see the same errors that Cline is seeing

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MCP Server Rules

Cline is already aware of your active MCP servers and what they are for, but when you have a lot of MCP servers enabled, it can be useful to define when to use each server.

Utilize a .clinerules file or custom instructions to support intelligent MCP server activation through keyword-based triggers, making Cline’s tool selection more intuitive and context-aware.

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How MCP Rules Work

MCP Rules group your connected MCP servers into functional categories and define trigger keywords that activate them automatically when detected in your conversations with Cline.

{
	"mcpRules": {
		"webInteraction": {
			"servers": ["firecrawl-mcp-server", "fetch-mcp"],
			"triggers": ["web", "scrape", "browse", "website"],
			"description": "Tools for web browsing and scraping"
		}
	}
}

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Configuration Structure

  1. Categories: Group related servers (e.g., “webInteraction”, “mediaAndDesign”)
  2. Servers: List server names in each category
  3. Triggers: Keywords that activate these servers
  4. Description: Human-readable category explanation

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Benefits of MCP Rules

  • Contextual Tool Selection: Cline selects appropriate tools based on conversation context
  • Reduced Friction: No need to manually specify which tool to use
  • Organized Capabilities: Logically group related tools and servers
  • Prioritization: Handle ambiguous cases with explicit priority ordering

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Example Usage

When you write “Can you scrape this website?”, Cline detects “scrape” and “website” as triggers, automatically selecting web-related MCP servers.

For finance tasks like “What’s Apple’s stock price?”, keywords like “stock” and “price” trigger finance-related servers.

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Quick Start Template

{
	"mcpRules": {
		"category1": {
			"servers": ["server-name-1", "server-name-2"],
			"triggers": ["keyword1", "keyword2", "phrase1", "phrase2"],
			"description": "Description of what these tools do"
		},
		"category2": {
			"servers": ["server-name-3"],
			"triggers": ["keyword3", "keyword4", "phrase3"],
			"description": "Description of what these tools do"
		},
		"category3": {
			"servers": ["server-name-4", "server-name-5"],
			"triggers": ["keyword5", "keyword6", "phrase4"],
			"description": "Description of what these tools do"
		}
	},
	"defaultBehavior": {
		"priorityOrder": ["category1", "category2", "category3"],
		"fallbackBehavior": "Ask user which tool would be most appropriate"
	}
}

Add this to your .clinerules file or to your custom instructions to make Cline’s MCP server selection more intuitive and context-aware.