> ## Documentation Index
> Fetch the complete documentation index at: https://arizeai-433a7140.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# MCP Tracing (TypeScript)

> Trace MCP (Model Context Protocol) clients and servers in TypeScript/Node.js

This module provides instrumentation for [MCP (Model Context Protocol)](https://modelcontextprotocol.io/) clients and servers, enabling context propagation between MCP clients and servers to unify traces.

<Note>
  The `@arizeai/openinference-instrumentation-mcp` instrumentor enables context propagation between MCP clients and servers. It does not generate its own telemetry—you still need to generate OpenTelemetry traces in both the client and server to see a unified trace.
</Note>

## Install

```bash theme={null}
npm install @arizeai/openinference-instrumentation-mcp @arizeai/phoenix-otel
```

## Setup

To instrument your MCP application, use the `register` function from `@arizeai/phoenix-otel` and set up the MCP instrumentation.

Create the `instrumentation.ts` file:

```typescript expandable theme={null}
import { register } from "@arizeai/phoenix-otel";
import { MCPInstrumentation } from "@arizeai/openinference-instrumentation-mcp";

// Initialize Phoenix tracing
const tracerProvider = register({
  projectName: "mcp-app",
  // If using Phoenix Cloud:
  // url: "https://app.phoenix.arize.com/s/your-space-name",
  // apiKey: process.env.PHOENIX_API_KEY,
  // If using self-hosted Phoenix:
  // url: "http://localhost:6006",
});

// Set up MCP instrumentation for context propagation
const instrumentation = new MCPInstrumentation();
instrumentation.enable();

console.log("MCP instrumentation registered");
```

## MCP Client Example

```typescript expandable theme={null}
import "./instrumentation.js";
import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";

async function main() {
  const transport = new StdioClientTransport({
    command: "node",
    args: ["./server.js"],
  });

  const client = new Client({
    name: "example-client",
    version: "1.0.0",
  }, {
    capabilities: {},
  });

  await client.connect(transport);

  // Call a tool on the MCP server
  const result = await client.callTool({
    name: "get_weather",
    arguments: { location: "San Francisco" },
  });

  console.log(result);
  await client.close();
}

main();
```

## MCP Server Example

```typescript expandable theme={null}
import "./instrumentation.js";
import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";

const server = new Server({
  name: "example-server",
  version: "1.0.0",
}, {
  capabilities: {
    tools: {},
  },
});

// Define a tool
server.setRequestHandler("tools/call", async (request) => {
  if (request.params.name === "get_weather") {
    const location = request.params.arguments?.location;
    return {
      content: [{
        type: "text",
        text: `Weather in ${location}: Sunny, 72°F`,
      }],
    };
  }
  throw new Error(`Unknown tool: ${request.params.name}`);
});

// List available tools
server.setRequestHandler("tools/list", async () => {
  return {
    tools: [{
      name: "get_weather",
      description: "Get the weather for a location",
      inputSchema: {
        type: "object",
        properties: {
          location: { type: "string" },
        },
        required: ["location"],
      },
    }],
  };
});

async function main() {
  const transport = new StdioServerTransport();
  await server.connect(transport);
}

main();
```

## Observe

With MCP instrumentation enabled, traces from your MCP client and server will be connected in Phoenix, allowing you to see the full request flow across client-server boundaries.

## Resources

* [NPM Package](https://www.npmjs.com/package/@arizeai/openinference-instrumentation-mcp)

* [OpenInference package for MCP](https://github.com/Arize-ai/openinference/tree/main/js/packages/openinference-instrumentation-mcp)

* [Model Context Protocol Documentation](https://modelcontextprotocol.io/)