Activity: Create an SSE server

Let's create an SSE server and also let's ensure we can reach it via clients like the Inspector and Visual Studio Code.

-1- Create the server

1. Create a file server-sse.ts in your existing project and add the following code:

   import express, { Request, Response } from "express";
   import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
   import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";

   Note how we're now using the following imports:

   • SSEServerTransport from @modelcontextprotocol/sdk/server/sse.js instead of StdioServerTransport.
   • express to create an Express server instead of using the StdioServerTransport directly.

   Let's move on to create the server.

2. Add the following code below the imports:

   const server = new McpServer({
     name: "example-server",
     version: "1.0.0"
   });
   
   const app = express();
   
   const transports: {[sessionId: string]: SSEServerTransport} = {};

   This creates a new instance of the McpServer class, which is the main entry point for creating an MCP server. Additionally, we create an Express server and a lookup object for storing the transports.

3. Let's implement the two endpoints of the server:

   app.get("/sse", async (_: Request, res: Response) => {
     const transport = new SSEServerTransport('/messages', res);
     transports[transport.sessionId] = transport;
     res.on("close", () => {
       delete transports[transport.sessionId];
     });
     await server.connect(transport);
   });
   
   app.post("/messages", async (req: Request, res: Response) => {
     const sessionId = req.query.sessionId as string;
     const transport = transports[sessionId];
     if (transport) {
       await transport.handlePostMessage(req, res);
     } else {
       res.status(400).send('No transport found for sessionId');
     }
   });
   
   app.listen(3001);

   Great, now we have the two mandatory endpoints.

4. Finally, let's add some tools to the server. Add the following code below the transports object, make sure you add it before the call to app.listen(3001):

   server.tool("random-joke", "A joke returned by the chuck norris api", {},
     async () => {
       const response = await fetch("https://api.chucknorris.io/jokes/random");
       const data = await response.json();
   
       return {
         content: [
           {
             type: "text",
             text: data.value
           }
         ]
       };
     }
   );

   This tool will return a random joke from the Chuck Norris API.

The code in server-sse.ts should look like this:

// server-sse.ts
import express, { Request, Response } from "express";
import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { SSEServerTransport } from "@modelcontextprotocol/sdk/server/sse.js";
import { z } from "zod";

// Create an MCP server
const server = new McpServer({
  name: "example-server",
  version: "1.0.0"
});

app = express();

app.get("/sse", async (_: Request, res: Response) => {
  const transport = new SSEServerTransport('/messages', res);
  transports[transport.sessionId] = transport;
  res.on("close", () => {
    delete transports[transport.sessionId];
  });
  await server.connect(transport);
});

app.get("/messages", async (req: Request, res: Response) => {
  const sessionId = req.query.sessionId as string;
  const transport = transports[sessionId];
  if (transport) {
    await transport.handlePostMessage(req, res);
  } else {
    res.status(400).send('No transport found for sessionId');
  }
});

app.tool("random-joke", "A joke returned by the chuck norris api", {},
  async () => {
    const response = await fetch("https://api.chucknorris.io/jokes/random");
    const data = await response.json();

    return {
      content: [
        {
          type: "text",
          text: data.value
        }
      ]
    };
  }
);

app.listen(3001);

-2- Test the server

To test the server, we will test it in two different ways:

• Using the Inspector, this is a great tool to quickly test your server and see the results in a nice UI.
• Using Visual Studio Code. This also provide a nice UI but as it is a code editor, it can make your code development easier depending on what features you add to your MCP server.

-1- Test the server using the Inspector

Clone the following project:

git clone https://github.com/softchris/hello-mcp
cd hello-mcp

Then run the following command:

npm install

note

For the inspector to work, you need to start up the server and the inspector separately

First, start the server by running the following command:

npm run start:server

Next, start the inspector by running the following command:

npm run inspect:server

This will kick off the Inspector and connect to the server.

You should see an inspector window like this:

Note how the following have been added:

• Transport: SSE
• URL: http://localhost:4321/sse

In the screenshot, I've already selected "Connect" and "Tools" and have gone on to select the "random-joke" tool and what you're looking at is the result of running the tool.

-2- Test the server using Visual Studio Code

Now we know the server is working great using the inspector, let's test it using Visual Studio Code.

Like we did before, let's add an entry to mcp.json file in the .vscode folder:

 "sse-server": {
    "type": "sse",
    "url": "http://localhost:4321/sse",
}

Important to note here is:

• The type is sse and not stdio.
• url needs to be specified AND unlike with an stdio server, you need to start up the server before you click the play button.

The complete mcp.json file should look like this:

{
    "inputs": [],
    "servers": {
        "sse-server": {
            "type": "sse",
            "url": "http://localhost:4321/sse",
        }
    }
}

To test the server do the following:

• Start it with npm run start:server.
• Click the play button in the .vscode/mcp.json file.

Try typing a prompt like so in the Visual Studio Code GitHub Copilot Chat window:

tell me a joke

You should see a result where it's asking to run a tool like this random-joke.

Summary

You've just a simple SSE server that can be used with the Inspector and Visual Studio Code. If you host this server somewhere other people can connect to it.