End-to-End MCP Tooling System with Vertex AI Gemini

This repository showcases an end-to-end implementation of the Model Context Protocol (MCP), demonstrating how to build a production-aligned MCP server and client that communicate via JSON-RPC 2.0 over STDIO and leverage Vertex AI Gemini for intelligent tool orchestration.

The system includes:

• An MCP server built using FastMCP, exposing structured tools
• An MCP client that launches the server as a subprocess and interacts with it over STDIO
• LLM-driven tool discovery, execution, and multi-step tool chaining
• Secure, cloud-native integration with Vertex AI Gemini using IAM-based authentication

This project emphasizes protocol correctness, async-safe system design, and real-world LLM tool orchestration patterns, making it suitable a production-quality foundation for MCP-based agent systems.

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🏗️ Architecture Diagram

Important distinction

• Terminal I/O → human interaction
• STDIO transport → machine-to-machine JSON-RPC communication

flowchart LR
    User["👤 User<br/>(CLI)"]

    subgraph Client["🧠 MCP Client"]
        Gemini["✨ Gemini (Vertex AI)<br/>Reasoning Engine"]
        Session["🔌 MCP ClientSession<br/>(JSON-RPC)"]
    end

    subgraph Server["🛠 MCP Server"]
        FastMCP["⚙️ FastMCP Runtime"]
        Tools["🌦 Weather Tools<br/>• get_forecast<br/>• get_alerts"]
    end

    User -->|"Query / Response"| Client
    Gemini -->|"Tool calls"| Session
    Session -->|"JSON-RPC 2.0"| FastMCP
    FastMCP --> Tools

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🏗️ Execution Sequence (End-to-End)

sequenceDiagram
    participant U as User (CLI)
    participant C as MCP Client
    participant L as Gemini (Vertex AI)
    participant S as MCP Server
    participant T as Weather Tools

    U->>C: Enter natural language query
    C->>L: Send prompt + tool schemas
    L->>C: Emit structured tool call
    C->>S: JSON-RPC call_tool request
    S->>T: Execute weather function
    T-->>S: Tool result
    S-->>C: JSON-RPC response
    C->>L: Provide tool output
    L-->>C: Final natural language response
    C-->>U: Display result

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Key Notes

• STDIO is used only for client ↔ server JSON-RPC
• Terminal I/O is strictly human interaction
• Gemini never calls tools directly — it requests, the client executes
• Tool chaining is handled by a while-loop on the client

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📁 Project Structure

End-to-End-MCP-Tooling-System-with-Vertex-AI-Gemini/
├── weather/
│   ├── weather.py        # MCP server: FastMCP runtime + weather tools
│   ├── client.py         # MCP client: Gemini reasoning + tool loop
│   ├── pyproject.toml    # uv project configuration & dependencies
│   ├── uv.lock           # Locked, reproducible dependency versions
│   ├── .gitignore        # Ignores .env, .venv, caches, OS artifacts
│   └── README.md         # Weather MCP module documentation
└── README.md             # Root project overview & architecture

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🚀 Features

• ✅ MCP server built using FastMCP
• ✅ STDIO-based JSON-RPC communication
• ✅ Tool discovery (list_tools)
• ✅ Tool execution (call_tool)
• ✅ Multi-round tool chaining using a proper loop
• ✅ Vertex AI Gemini integration (IAM-based auth)
• ✅ Async-safe lifecycle management with AsyncExitStack
• ✅ Clean dependency management using uv

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🛠️ Prerequisites

• Python 3.10+
• uv package manager
• Google Cloud project with:
  • Vertex AI enabled
  • Gemini model access
• Authenticated locally using:

  gcloud auth application-default login

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⚙️ Setup Instructions

Follow these steps to run the MCP server and client locally.

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1️⃣ Clone the repository

git clone https://github.com/AvinashBolleddula/End-to-End-MCP-Tooling-System-with-Vertex-AI-Gemini.git
cd End-to-End-MCP-Tooling-System-with-Vertex-AI-Gemini/weather

2️⃣ Create and activate a virtual environment

This project uses uv for fast and reproducible Python environments.

uv venv
source .venv/bin/activate

You should now see (.venv) in your terminal prompt.

3️⃣ Install dependencies

Install all required dependencies exactly as defined in pyproject.toml and uv.lock.

uv sync

4️⃣ Configure environment variables

Create a .env file inside the weather/ directory:

GOOGLE_CLOUD_PROJECT=your-gcp-project-id
GOOGLE_CLOUD_LOCATION=us-central1
GEMINI_MODEL=gemini-2.0-flash

Note Vertex AI uses IAM authentication, not API keys Ensure you are authenticated locally using:

gcloud auth application-default login

5️⃣ Run the MCP client and server

From inside the weather/ directory:

python client.py weather.py

If everything is configured correctly, you should see:

Connected to server with tools: ['get_alerts', 'get_forecast']
MCP Client Started!

You can now start interacting with the system via the terminal.