MCP Server Development Skill

Overview

The Model Context Protocol (MCP) is an open standard for connecting AI agents to external tools. This skill helps you build MCP servers using Azure Functions.

Architecture

code

┌─────────────────┐     ┌──────────────────────┐     ┌─────────────────┐
│  AI Agent       │     │  MCP Server          │     │  Your Logic     │
│  (Copilot)      │────▶│  (Azure Functions)   │────▶│  (Python)       │
│                 │◀────│  SSE Transport       │◀────│                 │
└─────────────────┘     └──────────────────────┘     └─────────────────┘

Creating an MCP Tool

Tool Definition Pattern

python

import json
import azure.functions as func

app = func.FunctionApp(http_auth_level=func.AuthLevel.FUNCTION)

# Define tool properties (JSON schema for parameters)
tool_properties = json.dumps([
    {
        "propertyName": "query",
        "propertyType": "string",
        "description": "The search query to execute"
    },
    {
        "propertyName": "limit",
        "propertyType": "number",
        "description": "Maximum number of results (default: 10)"
    }
])

@app.generic_trigger(
    arg_name="context",
    type="mcpToolTrigger",
    toolName="search_data",
    description="Search the database for records matching the query. Use when the user asks to find or search for specific data.",
    toolProperties=tool_properties
)
def search_data(context) -> str:
    """Search tool implementation."""
    content = json.loads(context)
    query = content["arguments"].get("query", "")
    limit = content["arguments"].get("limit", 10)
    
    # Your search logic here
    results = perform_search(query, limit)
    
    return json.dumps({
        "results": results,
        "count": len(results),
        "query": query
    })

Tool Property Types

Type	Description	Example
`string`	Text input	`"hello world"`
`number`	Integer or float	`42`, `3.14`
`boolean`	True/false	`true`, `false`
`array`	JSON array (as string)	`"[1, 2, 3]"`
`object`	JSON object (as string)	`'{"key": "value"}'`

VS Code MCP Configuration

Local Development (.vscode/mcp.json)

json

{
    "servers": {
        "my-mcp-server": {
            "type": "http",
            "url": "http://localhost:7071/runtime/webhooks/mcp"
        }
    }
}

Production (with authentication)

json

{
    "servers": {
        "my-mcp-server-prod": {
            "type": "http",
            "url": "https://my-app.azurewebsites.net/runtime/webhooks/mcp",
            "headers": {
                "x-functions-key": "${MCP_FUNCTION_KEY}"
            }
        }
    }
}

Testing MCP Tools

Via VS Code Copilot

•Press F1 → MCP: List Servers
•Verify your server is connected
•Open Copilot Chat → Switch to Agent Mode
•Your tools appear in the tools panel

Test Prompts

Tool	Test Prompt
`hello_mcp`	"Say hello"
`analyze_data`	"Analyze [1, 2, 3, 4, 5]"
`search_data`	"Search for Python tutorials"

Writing Good Tool Descriptions

The description field is critical — it's how Copilot decides when to use your tool.

Good Descriptions ✅

python

description="Analyze a list of numbers and return statistics including count, sum, mean, min, and max. Use when the user asks for data analysis or statistics."

Poor Descriptions ❌

python

description="Analyzes data"  # Too vague

Common Patterns

Tool with No Parameters

python

@app.generic_trigger(
    arg_name="context",
    type="mcpToolTrigger",
    toolName="get_status",
    description="Get the current system status",
    toolProperties="[]"  # Empty array for no parameters
)
def get_status(context) -> str:
    return json.dumps({"status": "healthy"})

Tool with Optional Parameters

python

# Mark as optional in description
tool_properties = json.dumps([{
    "propertyName": "format",
    "propertyType": "string",
    "description": "Output format: 'json' or 'text' (optional, default: json)"
}])

Error Handling

python

def my_tool(context) -> str:
    try:
        content = json.loads(context)
        # ... tool logic ...
        return json.dumps({"status": "success", "data": result})
    except json.JSONDecodeError:
        return json.dumps({"error": "Invalid JSON input"})
    except KeyError as e:
        return json.dumps({"error": f"Missing required parameter: {e}"})
    except Exception as e:
        logging.error(f"Tool error: {e}")
        return json.dumps({"error": str(e)})

Debugging Tips

•Check func start output — Tools should be listed
•View logs — logging.info() appears in terminal
•Test JSON parsing — Context comes as JSON string
•Verify MCP config — F1 → MCP: List Servers
•Restart Copilot — After config changes