MCP Client TS

TypeScript MCP Client Builder

Build MCP (Model Context Protocol) clients in TypeScript using code snippets and patterns from the official SDK.

Now includes advanced capability support: sampling handlers, elicitation, roots, dynamic discovery, resource subscriptions, and task support with persistence.

How It Works

1. Browse the snippet catalog below or in snippets/
2. Copy the snippets you need into your project
3. Customize the copied code for your use case
4. Connect to your MCP server and use tools/resources/prompts

Quick Start Decision Tree

Which Snippet Should I Start With?

Building an agentic app where an LLM decides when to use tools?
  └─> Use client-with-llm snippet
      Includes Claude integration, tool calling loop, interactive chat

Just need direct MCP server access (no LLM)?
  └─> Use client-setup snippet
      Basic connection, manual tool/resource/prompt calls

Which Transport Should I Use?

Connecting to a local process (CLI tool, desktop app)?
  └─> Use StdioClientTransport
      Examples: Claude Desktop, CLI applications, local dev servers

Connecting to a remote HTTP server?
  └─> Use StreamableHTTPClientTransport
      Examples: Cloud-hosted MCP servers, web services

Need to support legacy SSE-only servers?
  └─> Use StreamableHTTP with SSE fallback pattern
      See transport-http snippet for fallback example

Phase 1: Research

1.1 Identify Your Server

Before writing code, understand:

• What MCP server are you connecting to?
• How is the server started? (local process vs remote URL)
• Does the server require authentication?
• What tools/resources/prompts does it expose?

1.2 Browse Available Snippets

Phase 2: Implement

2.1 Initialize Project

mkdir my-mcp-client && cd my-mcp-client
npm init -y
npm install @modelcontextprotocol/sdk @anthropic-ai/sdk dotenv
npm install -D typescript @types/node
npx tsc --init
mkdir src

Note: The above installs the direct Anthropic API SDK. For other providers, see the provider options in the client-with-llm snippet.

Update tsconfig.json:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "Node16",
    "moduleResolution": "Node16",
    "rootDir": "./src",
    "outDir": "./dist",
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "types": ["node"]
  },
  "include": ["src/**/*"]
}

Update package.json:

{
  "type": "module",
  "scripts": {
    "build": "tsc",
    "start": "node dist/index.js"
  }
}

Create .env for API keys (choose based on your provider):

# Direct API
ANTHROPIC_API_KEY=your-api-key

# AWS Bedrock
AWS_ACCESS_KEY_ID=your-access-key
AWS_SECRET_ACCESS_KEY=your-secret-key
AWS_REGION=us-east-1

# Google Vertex AI
GOOGLE_CLOUD_PROJECT=your-project-id
GOOGLE_CLOUD_REGION=us-central1

# Azure (Foundry)
ANTHROPIC_FOUNDRY_API_KEY=your-api-key
ANTHROPIC_FOUNDRY_RESOURCE=your-resource.azure.anthropic.com

Create .gitignore:

node_modules/
dist/
build/
.env
*.log

2.2 Add Snippets

Copy snippets from this skill's snippets/ directory into your project:

snippets/
├── client/
│   ├── index.ts           # Basic client setup
│   └── with-llm.ts        # Agentic client with Claude
└── transports/
    ├── stdio.ts           # Local process transport
    └── http.ts            # Remote HTTP transport

Note: The client-with-llm snippet requires a Claude provider SDK:

npm install dotenv

# Choose ONE provider:
npm install @anthropic-ai/sdk            # Direct API
npm install @anthropic-ai/bedrock-sdk   # AWS Bedrock
npm install @anthropic-ai/vertex-sdk    # Google Vertex AI
npm install @anthropic-ai/foundry-sdk   # Azure (Foundry)

Copy snippets to your project:

cp snippets/client/index.ts /path/to/my-mcp-client/src/
cp snippets/transports/stdio.ts /path/to/my-mcp-client/src/

2.3 Customize and Connect

Each snippet includes:

• Source URL linking to official documentation
• Working code ready to customize

Modify the copied code:

1. Update client name and version
2. Configure the appropriate transport
3. Add your application logic
4. Handle tool results and resources

Phase 3: Test

3.1 Build

npm run build

3.2 Test Connection

Required: The client-with-llm snippet requires ANTHROPIC_API_KEY (or equivalent provider credentials) in your .env file before testing. Without it, you'll get: Could not resolve authentication method.

# Interactive mode with a local server
node dist/index.js path/to/server.js

# Interactive mode with an npx package
node dist/index.js @modelcontextprotocol/server-everything

# Non-interactive mode (single query)
node dist/index.js @modelcontextprotocol/server-everything "add 5 and 3"

3.3 Quality Checklist

• Client connects successfully to server
• Tools are listed correctly
• Tool calls return expected results
• Resources are readable
• Error handling is robust
• Connection cleanup on exit

Available Snippets Catalog

Client

Transports

Handlers (Server-Initiated Requests)

Features (Dynamic Discovery & Monitoring)

Capabilities

Stores

Quick Reference

Core Imports

import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js";

Basic Client Pattern

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

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

await client.connect(transport);

// Use the client
const tools = await client.listTools();
const result = await client.callTool({ name: "tool-name", arguments: {} });

// Cleanup
await client.close();

Multi-Server Pattern

import {
  connectToAllServers,
  aggregateTools,
  callTool,
  disconnectAll,
} from './multi-server.js';

// Connect to multiple servers
const clients = await connectToAllServers({
  "time": { url: "http://localhost:3001/mcp" },
  "weather": { url: "http://localhost:3002/mcp" },
});

// Get all tools with qualified names (server__tool)
const tools = await aggregateTools(clients);
// [{ name: "time__get-time", originalName: "get-time", serverName: "time", ... }]

// Call a tool using qualified name
const result = await callTool(clients, "weather__get-forecast", { city: "Seattle" });

// Cleanup
await disconnectAll(clients);

Server Instructions

MCP servers can provide instructions that describe how to use their tools effectively. These are returned during initialization and should be included in LLM system prompts:

// After connecting, retrieve server instructions
const instructions = client.getInstructions();

if (instructions) {
  console.log("Server instructions:", instructions);
  // Include in your LLM's system prompt for better tool usage
}

The client-with-llm snippet automatically includes server instructions in the Claude system prompt. If you want to add a base system prompt along with server instructions:

// Set a base system prompt (optional)
mcpClient.setSystemPrompt("You are a helpful assistant with access to MCP tools.");

// Server instructions will be appended automatically
// when processQuery() calls Claude

Related Skills

This skill focuses on building MCP clients with full protocol support. See also:

Why use mcp-client-ts instead of Claude Agent SDK?

• Need full MCP protocol (prompts, sampling, roots, logging, subscriptions, tasks)
• Building non-agent applications (IDEs, services, custom integrations)
• Need direct control over MCP client behavior

Reference Files

For deeper guidance, load these reference documents:

• TypeScript Client Patterns - SDK imports, transport options, API methods

MCP Documentation Server

For up-to-date protocol details, use the MCP docs server:

{
  "mcpServers": {
    "mcp-docs": {
      "type": "http",
      "url": "https://modelcontextprotocol.io/mcp"
    }
  }
}

Query the docs server for:

• "Example clients" - includes examples of both open source and closed source MCP clients
• Client feature support
• Protocol specification updates

External Resources

• MCP Specification - Official protocol documentation
• TypeScript SDK - Official SDK repository
• Build a Client Tutorial - Step-by-step guide
• Client Examples - Runnable examples

Building More Capable Clients

Most MCP clients only implement basic features. To build a more capable client that stands out, implement these advanced capabilities:

Capability Declaration

Declare capabilities during client initialization to enable server-initiated requests:

const client = new Client(
  { name: 'my-client', version: '1.0.0' },
  {
    capabilities: {
      // Allow server to request LLM completions (with tool support - MCP 2025-11-25)
      sampling: { tools: {} },

      // Allow server to request user input
      elicitation: {
        form: {},   // Structured input
        url: {}     // URL redirects (OAuth)
      },

      // Expose filesystem roots
      roots: {
        listChanged: true  // Notify on changes
      },

      // Enable task support for long-running operations
      tasks: {
        list: {},      // Support tasks/list
        cancel: {},    // Support tasks/cancel
        requests: {    // Task-augmented request types you can receive
          sampling: { createMessage: {} },
          elicitation: { create: {} },
        },
      }
    }
  }
);

Server-Initiated Requests

Sampling - Servers can request LLM completions:

import { CreateMessageRequestSchema } from '@modelcontextprotocol/sdk/client/index.js';

client.setRequestHandler(CreateMessageRequestSchema, async (request) => {
  // Call Claude API with request.params.messages
  return { role: 'assistant', content: { type: 'text', text: response }, model: 'claude-...' };
});

Elicitation - Servers can request user input:

import { ElicitRequestSchema } from '@modelcontextprotocol/sdk/client/index.js';

client.setRequestHandler(ElicitRequestSchema, async (request) => {
  // Prompt user based on request.params.requestedSchema
  return { action: 'accept', content: { confirm: true } };
});

Dynamic Discovery

React to server capability changes in real-time:

const client = new Client(
  { name: 'my-client', version: '1.0.0' },
  {
    capabilities: {},
    listChanged: {
      tools: {
        autoRefresh: true,
        onChanged: (err, tools) => {
          console.log('Tools updated:', tools?.map(t => t.name));
        }
      }
    }
  }
);

Resource Subscriptions

Subscribe to resources for live updates:

// Check if server supports subscriptions
const caps = client.getServerCapabilities();
if (caps?.resources?.subscribe) {
  await client.subscribeResource({ uri: 'file:///data.json' });

  client.setNotificationHandler(
    { method: 'notifications/resources/updated' },
    async (notification) => {
      const content = await client.readResource({ uri: notification.params.uri });
      console.log('Resource updated:', content);
    }
  );
}

Task Support

Handle long-running tool operations with progress tracking:

import {
  serverSupportsTasks,
  callToolWithTaskSupport,
  callToolAuto,
  listTasks,
  getTask,
  cancelTask,
} from './capabilities/tasks.js';

// Check if server supports tasks
if (serverSupportsTasks(client)) {
  // Call a tool with streaming progress updates
  const result = await callToolWithTaskSupport(client, 'long-running-tool', { arg: 'value' }, {
    onTaskCreated: (task) => console.log('Task started:', task.taskId),
    onTaskStatusUpdate: (task) => console.log('Status:', task.status, task.statusMessage),
  });

  // Or auto-detect: uses task mode if tool supports it, regular mode otherwise
  const tools = await client.listTools();
  const tool = tools.tools.find(t => t.name === 'my-tool');
  const autoResult = await callToolAuto(client, tool, { arg: 'value' });

  // Task management
  const tasks = await listTasks(client);
  const task = await getTask(client, 'task-id');
  await cancelTask(client, 'task-id');
}

For persistent task storage across restarts:

import { createPersistentTaskStore } from './stores/persistent-task-store.js';
import { join } from 'node:path';
import { homedir } from 'node:os';

const taskStore = createPersistentTaskStore({
  dataDir: join(homedir(), '.my-app', 'data'),
  persistenceEnabled: true,
  onLog: (msg) => console.log(msg),
});

const client = new Client(
  { name: 'my-client', version: '1.0.0' },
  { capabilities: { tasks: {} }, taskStore }
);

For handling task-augmented requests when the client is the receiver (bidirectional tasks):

import {
  createReceiverTaskManager,
  setupReceiverTaskHandlers,
  getReceiverTaskCapabilities,
  emitTaskStatusNotification,
} from './capabilities/tasks-receiver.js';

// Create task manager for receiver-side tasks
const taskManager = createReceiverTaskManager({
  ttl: 300000,  // 5 minutes
  onLog: (msg) => console.log(msg),
});

// Set up request handlers for tasks/list, tasks/get, etc.
setupReceiverTaskHandlers(client, taskManager);

// Get capability declaration for client initialization
const taskCapabilities = getReceiverTaskCapabilities({
  sampling: true,      // Support task-augmented sampling requests
  elicitation: true,   // Support task-augmented elicitation requests
});

// In your sampling handler, create receiver tasks:
client.setRequestHandler(CreateMessageRequestSchema, async (request) => {
  // Check if this is a task-augmented request
  if (request.params.task) {
    const record = taskManager.createTask({
      ttl: request.params.task.ttl,
      initialStatus: 'working',
      statusMessage: 'Processing sampling request...',
    });

    // Process asynchronously, then complete:
    // taskManager.completeTask(record.task.taskId, result);
    // await emitTaskStatusNotification(client, record.task);

    return { task: record.task };  // Return CreateTaskResult
  }

  // Normal non-task flow...
});

Use Case Examples

Beyond chatbots, capable MCP clients can power:

• IDE Integrations: Expose project roots, handle file operations, provide completions
• Workflow Automation: Orchestrate multi-tool workflows, handle confirmations via elicitation
• Monitoring Dashboards: Subscribe to resources for live data, receive server logs
• AI-Powered CLI Tools: Use sampling for intelligent command suggestions

See the MCP Reference Client for a complete implementation.

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