🔌 dart_mcp_client

A lightweight, pure Dart client implementation of the Model Context Protocol (MCP) standard.

Works with any LLM framework or Dart backend/CLI/desktop application. Supports both local subprocesses (Stdio) and remote servers (Streamable HTTP / SSE) with zero Flutter or platform dependencies.

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✨ Features

• 🚀 Dual Transport Support:
  • Stdio (StdioMcpClient): Launch and communicate with local Node.js (npx), Python (uvx), or native binary MCP servers.
  • HTTP (HttpMcpClient): Connect to remote MCP servers over Streamable HTTP and Server-Sent Events (SSE) (MCP 2025 specification).
• 🛠️ Complete Protocol Implementation:
  • tools/list & tools/call for tool discovery and execution.
  • resources/list & resources/read for context and document access.
  • prompts/list & prompts/get for templated prompt retrieval.
• 🛡️ Battle-Tested Architecture:
  • Request/Response pairing with timeout protection.
  • Windows command resolution (runInShell for .cmd/.bat).
  • Diagnostic logging and real-time stderr streaming.
  • Fail-closed error handling and clean disconnects.

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📦 Installation

Add dart_mcp_client to your pubspec.yaml:

dependencies:
  dart_mcp_client: ^1.0.0

Or install via Dart CLI:

dart pub add dart_mcp_client

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🚀 Quick Start

1. Connecting to a Local Stdio Server (e.g. Memory Server)

import 'package:dart_mcp_client/dart_mcp_client.dart';

void main() async {
  final config = McpServerConfig(
    id: 'memory-server',
    name: 'Memory Server',
    transport: McpTransport.stdio,
    command: 'npx',
    args: ['-y', '@modelcontextprotocol/server-memory'],
  );

  final client = StdioMcpClient(
    config,
    onLog: (msg) => print('[LOG] $msg'),
    onStderr: (err) => print('[STDERR] $err'),
  );

  // Connect and perform initial handshake
  await client.connect();

  // Discover available tools
  final tools = await client.getTools();
  for (final tool in tools) {
    print('Discovered tool: ${tool.name} - ${tool.description}');
  }

  // Call a tool
  final result = await client.callTool('create_graph', {});
  print('Result: ${result.text}');

  // Disconnect when done
  await client.disconnect();
}

2. Connecting to a Remote HTTP Server

import 'package:dart_mcp_client/dart_mcp_client.dart';

void main() async {
  final config = McpServerConfig(
    id: 'remote-weather',
    name: 'Weather MCP',
    transport: McpTransport.http,
    url: 'https://api.example.com/mcp',
  );

  final client = HttpMcpClient(config);
  await client.connect();

  final tools = await client.getTools();
  final weather = await client.callTool('get_forecast', {'city': 'Istanbul'});
  print(weather.text);

  await client.disconnect();
}

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🏗️ Architecture

graph TD
    A[Dart App / LLM Agent] --> B[McpClientBase]
    B --> C[StdioMcpClient]
    B --> D[HttpMcpClient]
    C -->|stdin / stdout JSON-RPC| E[Local MCP Server (npx / uvx / binary)]
    D -->|HTTP POST & SSE Streams| F[Remote MCP Server]

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🧪 Testing

Run the test suite:

dart test

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📄 License

This project is licensed under the MIT License - see the LICENSE file for details.