Model Context Protocol

My first MCP Server (Stock Market)

This is my first MCP (Model Context Protocol) server project. The goal is to build a small and useful service around stock market data using Python and yfinance, following the official MCP guide: MCP with Python

What it can do (tools)

Planned / supported commands:

• Get stock data for a ticker: STOCK_TICKER

• Get stock data for multiple tickers: [list of tickers]

• Search by sector (returns top companies for that sector)

• Get latest news for a ticker

Specific goals

• Implement the features above using Python + yfinance

• Build the MCP Server

• Golden: Run it inside a Docker container (so the service starts/stops only when requested)

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Getting started

Logging (important for debugging)

Note

When working with MCP over stdio, prefer stderr for debug output, or use logging.

import sys
import logging

# ❌ Bad (STDIO)
print("Processing request")

# ✅ Good (STDIO)
print("Processing request", file=sys.stderr)

# ✅ Good (STDIO)
logging.info("Processing request")

Environment setup (uv)

You need uv to manage the virtual environment and dependencies:

uv venv
source .venv/bin/activate

uv add --dev "mcp[cli]" httpx yfinance
touch yFinance.py

Then configure VS Code to use the .venv interpreter.

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Notes about yfinance

I’m using the Yahoo Finance wrapper library yfinance. Documentation: yfinance reference

For now, I’m focusing on:

• ticker data (single and multiple)

• sector search (top companies)

• news section

---

Current implementation

Sector search change

I modified the search tool so it works by sector key and returns the top companies of that sector.

News section

I added a tool that fetches the latest news for a given ticker.

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Code

The main server script currently looks like this:

import sys
from typing import Any

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

# Initialize FastMCP server
mcp = FastMCP("yFinance")

# Constants
NWS_API_BASE = "https://api.yfinance.gov"
USER_AGENT = "yFinance-app/1.0"

# Allowed sector keys for yfinance Sector API
SECTOR_KEYS: list[str] = [
    # basic-materials
    "basic-materials",
    "agricultural-inputs",
    "aluminum",
    "building-materials",
    "chemicals",
    "coking-coal",
    "copper",
    "gold",
    "lumber-wood-production",
    "other-industrial-metals-mining",
    "other-precious-metals-mining",
    "paper-paper-products",
    "silver",
    "specialty-chemicals",
    "steel",
    # communication-services
    "communication-services",
    "advertising-agencies",
    "broadcasting",
    "electronic-gaming-multimedia",
    "entertainment",
    "internet-content-information",
    "publishing",
    "telecom-services",
    # energy
    "energy",
    "oil-gas-drilling",
    "oil-gas-e&p",
    "oil-gas-equipment-services",
    "oil-gas-integrated",
    "oil-gas-midstream",
    "oil-gas-refining-marketing",
    "thermal-coal",
    "uranium",
    # healthcare
    "healthcare",
    "biotechnology",
    "diagnostics-research",
    "drug-manufacturers—general",
    "drug-manufacturers—specialty-generic",
    "health-information-services",
    "healthcare-plans",
    "medical-care-facilities",
    "medical-devices",
    "medical-distribution",
    "medical-instruments-supplies",
    "pharmaceutical-retailers",
    # industrials
    "industrials",
    "aerospace-defense",
    "airlines",
    "airports-air-services",
    "building-products-equipment",
    "business-equipment-supplies",
    "conglomerates",
    "consulting-services",
    # technology
    "technology",
    "communication-equipment",
    "computer-hardware",
    "consumer-electronics",
    "electronic-components",
    "electronics-computer-distribution",
    "information-technology-services",
    "scientific-technical-instruments",
    "semiconductor-equipment-materials",
    "semiconductors",
    "software—application",
    "software—infrastructure",
    "solar",
]

"""
Otros posibles sectores que se podrían incorporar son:

# consumer-cyclical
...
"""

# Helper functions for the yfinance API
async def fetch_stock_data(ticker: str) -> Any:
    try:
        print(f"Fetching stock data for ticker: {ticker}", file=sys.stderr)

        dat = yf.Ticker(ticker)
        dat.history(period="1mo")
        dat.option_chain(dat.options[0]).calls

        return {
            "info": dat.info,
            "calendar": dat.calendar,
            "analyst_price_targets": (
                dat.analyst_price_targets.to_dict()
                if dat.analyst_price_targets is not None
                else None
            ),
            "quarterly_income_stmt": (
                dat.quarterly_income_stmt.to_dict()
                if dat.quarterly_income_stmt is not None
                else None
            ),
        }
    except Exception as e:
        print(
            f"Error fetching stock data for ticker {ticker}: {str(e)}",
            file=sys.stderr,
        )
        raise


async def fetch_stocks_data(tickers: list[str]) -> Any:
    json_data: list[Any] = []

    try:
        for ticker in tickers:
            json_data.append(await fetch_stock_data(ticker))
        return json_data
    except Exception as e:
        print(
            f"Error fetching stock data for tickers {tickers}: {str(e)}",
            file=sys.stderr,
        )
        raise


async def search_sector(sector_key: str) -> Any:
    try:
        print(f"Searching for companies in sector: {sector_key}", file=sys.stderr)

        df = yf.Sector(sector_key).top_companies
        if df is None:
            return []

        return df.reset_index(drop=True).to_dict(orient="records")
    except Exception as e:
        print(f"Error searching for sector {sector_key}: {str(e)}", file=sys.stderr)
        raise


async def latest_news(ticker: str) -> Any:
    ticker_search = yf.Search(ticker, news_count=10)
    news = ticker_search.news
    nav = ticker_search.nav

    return {"news": news, "navigation_links": nav}


# Register MCP functions
@mcp.tool()
async def get_stock_data(ticker: str) -> Any:
    """Fetch stock data for a given ticker symbol."""
    return await fetch_stock_data(ticker)


@mcp.tool()
async def get_stocks_data(tickers: list[str]) -> Any:
    """Fetch stock data for multiple ticker symbols."""
    return await fetch_stocks_data(tickers)


@mcp.tool(
    description=(
        """Search for companies in a given sector. The `sector_key` must be one of the allowed values understood by yfinance's Sector API. Valid values are: basic-materials, agricultural-inputs, aluminum, building-materials, chemicals, coking-coal, copper, gold, lumber-wood-production, other-industrial-metals-mining, other-precious-metals-mining, other-precious-metals-mining, paper-paper-products, silver, specialty-chemicals, steel, communication-services, advertising-agencies, broadcasting, electronic-gaming-multimedia, entertainment, internet-content-information, publishing, telecom-services, energy, oil-gas-drilling, oil-gas-e&p, oil-gas-equipment-services, oil-gas-integrated, oil-gas-midstream, oil-gas-refining-marketing, thermal-coal, uranium, healthcare, biotechnology, diagnostics-research, drug-manufact"""
    ),
    meta={"version": "1.0", "author": "Mk"},
)
async def search_sector_tool(sector_key: str) -> Any:
    if sector_key not in SECTOR_KEYS:
        raise ValueError(
            f"Invalid sector_key '{sector_key}'. Must be one of: {', '.join(SECTOR_KEYS)}"
        )

    return await search_sector(sector_key)


@mcp.tool()
async def get_latest_news(ticker: str) -> Any:
    """Fetch the latest news for a given ticker symbol."""
    return await latest_news(ticker)


# Start the MCP server
def main() -> None:
    print("Starting yFinance MCP server...", file=sys.stderr)

    try:
        mcp.run(transport="stdio")
    except Exception as e:
        print(f"Error starting yFinance MCP server: {str(e)}", file=sys.stderr)
        raise


if __name__ == "__main__":
    main()

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Testing

Testing failed a bit because mcp.tool() has some specific parameters that I can use to improve the tool definitions and overall quality.

I updated the script, added the configuration in Claude, and now I’m debugging until everything works properly.

Resultado: