Building Custom MCP Servers

This guide provides a comprehensive walkthrough of building a custom MCP (Model Context Protocol) server from scratch, leveraging the powerful AI capabilities of Cline. The example used will be building a "GitHub Assistant Server" to illustrate the process.

Understanding MCP and Cline's Role in Building Servers

What is MCP?

The Model Context Protocol (MCP) acts as a bridge between large language models (LLMs) like Claude and external tools and data. MCP consists of two key components:

• MCP Hosts: These are applications that integrate with LLMs, such as Cline, Claude Desktop, and others.

• MCP Servers: These are small programs specifically designed to expose data or specific functionalities to the LLMs through the MCP.

This setup is beneficial when you have an MCP-compliant chat interface, like Claude Desktop, which can then leverage these servers to access information and execute actions.

Why Use Cline to Create MCP Servers?

Cline streamlines the process of building and integrating MCP servers by utilizing its AI capabilities to:

• Understand Natural Language Instructions: You can communicate with Cline in a way that feels natural, making the development process intuitive and user-friendly.

• Clone Repositories: Cline can directly clone existing MCP server repositories from GitHub, simplifying the process of using pre-built servers.

• Build Servers: Once the necessary code is in place, Cline can execute commands like npm run build to compile and prepare the server for use.

• Handle Configuration: Cline manages the configuration files required for the MCP server, including adding the new server to the cline_mcp_settings.json file.

• Assist with Troubleshooting: If errors arise during development or testing, Cline can help identify the cause and suggest solutions, making debugging easier.

Building a GitHub Assistant Server Using Cline: A Step-by-Step Guide

This section demonstrates how to create a GitHub Assistant server using Cline. This server will be able to interact with GitHub data and perform useful actions:

1. Defining the Goal and Initial Requirements

First, you need to clearly communicate to Cline the purpose and functionalities of your server:

• Server Goal: Inform Cline that you want to build a "GitHub Assistant Server". Specify that this server will interact with GitHub data and potentially mention the types of data you are interested in, like issues, pull requests, and user profiles.

• Access Requirements: Let Cline know that you need to access the GitHub API. Explain that this will likely require a personal access token (GITHUB_TOKEN) for authentication.

• Data Specificity (Optional): You can optionally tell Cline about specific fields of data you want to extract from GitHub, but this can also be determined later as you define the server's tools.

2. Cline Initiates the Project Setup

Based on your instructions, Cline starts the project setup process:

• Project Structure: Cline might ask you for a name for your server. Afterward, it uses the MCP create-server tool to generate the basic project structure for your GitHub Assistant server. This usually involves creating a new directory with essential files like package.json, tsconfig.json, and a src folder for your TypeScript code. \

• Code Generation: Cline generates starter code for your server, including:

  • File Handling Utilities: Functions to help with reading and writing files, commonly used for storing data or logs. \

  • GitHub API Client: Code to interact with the GitHub API, often using libraries like @octokit/graphql. Cline will likely ask for your GitHub username or the repositories you want to work with. \

  • Core Server Logic: The basic framework for handling requests from Cline and routing them to the appropriate functions, as defined by the MCP. \

• Dependency Management: Cline analyzes the code and identifies necessary dependencies, adding them to the package.json file. For example, interacting with the GitHub API will likely require packages like @octokit/graphql, graphql, axios, or similar. \

• Dependency Installation: Cline executes npm install to download and install the dependencies listed in package.json, ensuring your server has all the required libraries to function correctly. \

• Path Corrections: During development, you might move files or directories around. Cline intelligently recognizes these changes and automatically updates file paths in your code to maintain consistency.

• Configuration: Cline will modify the cline_mcp_settings.json file to add your new GitHub Assistant server. This will include:

  • Server Start Command: Cline will add the appropriate command to start your server (e.g., npm run start or a similar command).

  • Environment Variables: Cline will add the required GITHUB_TOKEN variable. Cline might ask you for your GitHub personal access token, or it might guide you to safely store it in a separate environment file. \

• Progress Documentation: Throughout the process, Cline keeps the "Memory Bank" files updated. These files document the project's progress, highlighting completed tasks, tasks in progress, and pending tasks.

3. Testing the GitHub Assistant Server

Once Cline has completed the setup and configuration, you are ready to test the server's functionality:

• Using Server Tools: Cline will create various "tools" within your server, representing actions or data retrieval functions. To test, you would instruct Cline to use a specific tool. Here are examples related to GitHub:

  • get_issues: To test retrieving issues, you might say to Cline, "Cline, use the get_issues tool from the GitHub Assistant Server to show me the open issues from the 'cline/cline' repository." Cline would then execute this tool and present you with the results.

  • get_pull_requests: To test pull request retrieval, you could ask Cline to "use the get_pull_requests tool to show me the merged pull requests from the 'facebook/react' repository from the last month." Cline would execute this tool, using your GITHUB_TOKEN to access the GitHub API, and display the requested data. \

• Providing Necessary Information: Cline might prompt you for additional information required to execute the tool, such as the repository name, specific date ranges, or other filtering criteria.

• Cline Executes the Tool: Cline handles the communication with the GitHub API, retrieves the requested data, and presents it in a clear and understandable format.

4. Refining the Server and Adding More Features

Development is often iterative. As you work with your GitHub Assistant Server, you'll discover new functionalities to add, or ways to improve existing ones. Cline can assist in this ongoing process:

• Discussions with Cline: Talk to Cline about your ideas for new tools or improvements. For example, you might want a tool to create_issue or to get_user_profile. Discuss the required inputs and outputs for these tools with Cline.

• Code Refinement: Cline can help you write the necessary code for new features. Cline can generate code snippets, suggest best practices, and help you debug any issues that arise.

• Testing New Functionalities: After adding new tools or functionalities, you would test them again using Cline, ensuring they work as expected and integrate well with the rest of the server.

• Integration with Other Tools: You might want to integrate your GitHub Assistant server with other tools. For instance, in the "github-cline-mcp" source, Cline assists in integrating the server with Notion to create a dynamic dashboard that tracks GitHub activity. \

By following these steps, you can create a custom MCP server from scratch using Cline, leveraging its powerful AI capabilities to streamline the entire process. Cline not only assists with the technical aspects of building the server but also helps you think through the design, functionalities, and potential integrations.