How to Build an MCP Server in TypeScript

steps

1. Initialize a TypeScript Project:

   • Start by creating a new directory for your project.
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   mkdir mcp-server
   cd mcp-server
   npm init -y

   • Install required dependencies:
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   npm install mcp-sdk @types/node typescript ts-node

2. Set Up TypeScript Configuration: Generate a tsconfig.json file:

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   npx tsc --init

   Modify tsconfig.json:

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   {
     "compilerOptions": {
       "target": "ES2020",
       "module": "commonjs",
       "outDir": "./dist",
       "strict": true,
       "esModuleInterop": true
     }
   }

3. Create Entry Files:

   • Set up the src directory:
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   mkdir src
   touch src/index.ts

   • In src/index.ts:
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   import { createServer, Tool } from "mcp-sdk";
   
   const server = createServer();
   
   const helloWorldTool: Tool = {
     name: "hello_world",
     description: "A simple Hello World tool",
     inputParameters: { name: { type: "string", description: "Your name" } },
     async execute({ name }) {
       return { greeting: `Hello World, ${name}!` };
     },
   };
   
   server.addTool(helloWorldTool);
   server.start();
   console.log("MCP server started.");

4. Run and Test the Server: Use npm scripts to run the server:

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   npx ts-node src/index.ts

5. Customize for Open Library API: Replace the content of helloWorldTool with a tool to interact with Open Library:

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   import fetch from "node-fetch";
   
   const searchBooksTool: Tool = {
     name: "search_books",
     description: "Search books using Open Library API",
     inputParameters: {
       query: { type: "string", description: "Search keywords" },
       limit: { type: "number", description: "Number of results", optional: true },
       page: { type: "number", description: "Page number", optional: true },
     },
     async execute({ query, limit = 10, page = 1 }) {
       const response = await fetch(
         `https://openlibrary.org/search.json?q=${encodeURIComponent(query)}&limit=${limit}&page=${page}`
       );
       const data = await response.json();
       return data.docs
         .slice(0, limit)
         .map((book: any) => ({
           title: book.title,
           author: book.author_name?.join(", "),
           year: book.first_publish_year,
         }));
     },
   };
   
   server.addTool(searchBooksTool);

6. Test with MCP Inspector: Run MCP Inspector to debug and validate the server functionality:

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   npx mcp-inspector

   • Follow the prompts to connect MCP Inspector to your running server.
   • Use MCP Inspector to call the search_books tool and verify the results.

steps

1. Start your server using:
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   npx ts-node src/index.ts

2. Launch MCP Inspector with:
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   npx mcp-inspector

3. Connect MCP Inspector to your running server by specifying the command as node dist/index.js (adjust path if needed).
4. List the tools available by running the list command in the simple inspector.
5. Use input parameters like query, limit, and page to verify the output of your search_books tool.