The first MCP Server I ever installed

Here's the tutorial that got me started:

https://www.kdnuggets.com/building-a-simple-mcp-server

But I am not good with python (yet), so I had to dink around a lot to get it to work.

Here the steps (I did this on Windows)...

First, make sure you have at least version 3.10 of Python installed because some of the packages we use will not work with older versions.

Create a virtual envirnoment for the project:

python -m venv my-env

Activate the virtual environment:

my-env\\Scripts\\activate

Note that (my-env) will appear at the beginning of the terminal command line.

Install the packages we'll be using:

pip install "mcp[cli]" yfinance

Create a file named stock_price_server.py in the current folder (not inside the my-env folder), and add this code to it:

from mcp.server.fastmcp import FastMCP
import yfinance as yf

# Create an MCP server with a custom name
mcp = FastMCP("Stock Price Server")

@mcp.tool()
def get_stock_price(symbol: str) -> float:
    """
    Retrieve the current stock price for the given ticker symbol.
    Returns the latest closing price as a float.
    """
    try:
        ticker = yf.Ticker(symbol)
        # Get today's historical data; may return empty if market is closed or symbol is invalid.
        data = ticker.history(period="1d")
        if not data.empty:
            # Use the last closing price from today's data
            price = data['Close'].iloc[-1]
            return float(price)
        else:
            # As a fallback, try using the regular market price from the ticker info
            info = ticker.info
            price = info.get("regularMarketPrice", None)
            if price is not None:
                return float(price)
            else:
                return -1.0  # Indicate failure
    except Exception:
        # Return -1.0 to indicate an error occurred when fetching the stock price
        return -1.0

@mcp.resource("stock://{symbol}")
def stock_resource(symbol: str) -> str:
    """
    Expose stock price data as a resource.
    Returns a formatted string with the current stock price for the given symbol.
    """
    price = get_stock_price(symbol)
    if price < 0:
        return f"Error: Could not retrieve price for symbol '{symbol}'."
    return f"The current price of '{symbol}' is ${price:.2f}."

@mcp.tool()
def get_stock_history(symbol: str, period: str = "1mo") -> str:
    """
    Retrieve historical data for a stock given a ticker symbol and a period.
    Returns the historical data as a CSV formatted string.
    
    Parameters:
        symbol: The stock ticker symbol.
        period: The period over which to retrieve historical data (e.g., '1mo', '3mo', '1y').
    """
    try:
        ticker = yf.Ticker(symbol)
        data = ticker.history(period=period)
        if data.empty:
            return f"No historical data found for symbol '{symbol}' with period '{period}'."
        # Convert the DataFrame to a CSV formatted string
        csv_data = data.to_csv()
        return csv_data
    except Exception as e:
        return f"Error fetching historical data: {str(e)}"

@mcp.tool()
def compare_stocks(symbol1: str, symbol2: str) -> str:
    """
    Compare the current stock prices of two ticker symbols.
    Returns a formatted message comparing the two stock prices.
    
    Parameters:
        symbol1: The first stock ticker symbol.
        symbol2: The second stock ticker symbol.
    """
    price1 = get_stock_price(symbol1)
    price2 = get_stock_price(symbol2)
    if price1 < 0 or price2 < 0:
        return f"Error: Could not retrieve data for comparison of '{symbol1}' and '{symbol2}'."
    if price1 > price2:
        result = f"{symbol1} (${price1:.2f}) is higher than {symbol2} (${price2:.2f})."
    elif price1 < price2:
        result = f"{symbol1} (${price1:.2f}) is lower than {symbol2} (${price2:.2f})."
    else:
        result = f"Both {symbol1} and {symbol2} have the same price (${price1:.2f})."
    return result

if __name__ == "__main__":
    mcp.run()

Make sure you have Claude Desktop running, apparently that acts as the MCP server.

Run this command from the virtual environment terminal:

mcp dev stock_price_server.py

This will launch the mcp inspector web app that you can use to test your program. The port number it used was 6274, so go to: ** http://127.0.0.1:6274**.

Press the Connect button.

Click on the Tools tab, then click List Tools, this will display the tools that are created in the python program.

Click the get_stock_price tool, then enter a stock ticker symbol in the symbol textbox and click Run tool. It will return the price.

You can continue to experiment with the other tools in the same way.

To install the tool into Claude Desktop, run this command:

mcp install stock_price_server.py --name "Stock Price Server"

As a side note, when you are done with the virtual environment, press ctrl-c in the terminal to shut down the inspector, then deactivate the virtual environment:

my-env\\Scripts\\deactivate

The mcp install command did not work for me, so I updated the config file manually. claude_desktop_config.json, which is located at C:\Users\MYHOMEDIR\AppData\Roaming\Claude (Note that I already had a 'weather' mcp server install, I just added the 'Stock Price Server')

{
  "mcpServers": {
      "weather": {
          "command": "node",
          "args": [
              "C:\\Users\\MYHOMEDIR\\Desktop\\doc_root\\mcp-server\\build\\index.js"
          ]
      },
      "Stock Price Server": {
          "command": "C:\\Users\\MYHOMEDIR\\Desktop\\python-stuff\\my-mcp\\Scripts\\python.exe",
          "args": [
              "C:\\Users\\MYHOMEDIR\\Desktop\\python-stuff\\stock_price_server.py"
          ]
      }
  }
}

Then I had to use Task Manager to kill the Claude app and restart it. After that, the 3 new tools showed up!

To make use of the MCP server tools, enter a prompt into Claude like this: 'Could you please compare the prices of Microsoft and Tesla stocks?' Claude will detect that the tools are relevant to the prompt and show an pop up that asks if it may use them.

Here's another prompt, which will invoke get_stock_history tool: "Could you please provide the historical data for Tesla over the past month?"