MCP — Client & Server

Toolpack SDK supports the Model Context Protocol (MCP) in both directions:

• MCP Client — bridge any external MCP server into Toolpack as first-class tools
• MCP Server — expose Toolpack's 100+ built-in tools (or a filtered subset) to any MCP client: Claude Desktop, Cursor, or your own agents

What is MCP?

The Model Context Protocol is an open standard that defines how AI models can interact with external tools and data sources. MCP servers provide a standardized way to expose tools, resources, and prompts to AI assistants.

MCP Client — Consuming External MCP Servers

Setting Up MCP Servers

To integrate MCP servers with Toolpack, you need to:

1. Configure your MCP server connections
2. Create an MCP tool project
3. Register the tools with your Toolpack instance

Basic Configuration

import { Toolpack, createMcpToolProject } from 'toolpack-sdk';

const mcpConfig = {
  servers: [
    {
      name: 'filesystem',
      displayName: 'File System Tools',
      command: 'npx',
      args: ['-y', '@modelcontextprotocol/server-filesystem', '/path/to/allowed/directory'],
      autoConnect: true,
      toolPrefix: 'mcp.fs.',
    },
    {
      name: 'chrome-devtools',
      displayName: 'Chrome DevTools',
      command: 'npx',
      args: ['-y', 'chrome-devtools-mcp'],
      autoConnect: true,
      toolPrefix: 'mcp.chrome.',
    },
  ],
  defaultTimeoutMs: 30000,
  autoReconnect: true,
};

const mcpTools = await createMcpToolProject(mcpConfig);

const sdk = await Toolpack.init({
  provider: 'openai',
  tools: true,
  customTools: [mcpTools],
});

Configuration Options

Property	Type	Description
servers	McpServerConfig[]	Array of MCP server configurations
defaultTimeoutMs	number	Default timeout for tool calls (30 seconds)
autoReconnect	boolean	Automatically reconnect to servers on failure

Server Configuration

Each server in the servers array supports:

Property	Type	Required	Description
name	string	Yes	Unique identifier for the server
displayName	string	No	Human-readable name for the server
command	string	Yes	Command to start the MCP server
args	string[]	No	Arguments to pass to the command
autoConnect	boolean	No	Connect automatically on startup
toolPrefix	string	No	Prefix for tool names from this server

Using MCP Tools

Once configured, MCP tools are automatically available to your AI agents:

// List all available MCP tools
const allTools = await sdk.listTools();
const mcpTools = allTools.filter(tool => tool.category === 'mcp');
console.log('MCP Tools:', mcpTools.map(t => t.name));

// Use MCP tools in AI queries
const response = await sdk.generate(
  'Use the filesystem tools to list files in the current directory and analyze their contents.',
  'openai'
);
console.log(response.content);

Advanced Usage

Tool Restrictions and Modes

You can restrict MCP tools to specific modes or workflows:

import { createMode } from 'toolpack-sdk';

// Create a mode that only allows filesystem MCP tools
const fileMode = createMode({
  name: 'file-explorer',
  description: 'Mode for file system exploration using MCP tools',
  toolFilter: (tool) => tool.name.startsWith('mcp.fs.'),
});

const sdk = await Toolpack.init({
  provider: 'openai',
  tools: true,
  customTools: [mcpTools],
  modes: [fileMode],
});

Error Handling

MCP tool calls can fail due to network issues or server errors. Toolpack handles these gracefully:

try {
  const response = await sdk.generate('Execute an MCP tool operation', 'openai');
  console.log(response.content);
} catch (error) {
  if (error.message.includes('MCP')) {
    console.log('MCP server error:', error.message);
  } else {
    console.log('Other error:', error.message);
  }
}

Cleanup

Always disconnect MCP servers when shutting down:

import { disconnectMcpToolProject } from 'toolpack-sdk';

await disconnectMcpToolProject(mcpTools);
await sdk.shutdown?.();

Available MCP Servers

Popular MCP servers you can integrate:

• File System Server: Access and manipulate files and directories
• Chrome DevTools: Control web browsers and inspect pages
• Git Server: Interact with Git repositories
• SQLite Server: Query SQLite databases
• GitHub Server: Access GitHub APIs and repositories

Troubleshooting

Common Issues

1. Server Connection Failed: Ensure the MCP server command and arguments are correct
2. Tool Not Found: Verify the server is running and exposing the expected tools
3. Timeout Errors: Increase defaultTimeoutMs for long-running operations
4. Permission Denied: Check that the server has appropriate access to required resources

Debugging

Enable detailed logging to troubleshoot MCP issues:

const sdk = await Toolpack.init({
  provider: 'openai',
  tools: true,
  customTools: [mcpTools],
  logLevel: 'debug',
});

---

MCP Server — Exposing Toolpack to MCP Clients

sdk.startMcpServer() turns Toolpack into a fully-spec-compliant MCP server. Any MCP client — Claude Desktop, Cursor, or your own code — can connect and call Toolpack's tools.

Minimal HTTP server

const sdk = await Toolpack.init({ provider: 'anthropic', tools: true });

const handle = await sdk.startMcpServer({
  transport: 'http',
  port: 3000,
});

console.log(`MCP server on port ${handle.port}, ${handle.toolCount} tools exposed`);
// handle.stop() to shut down

stdio (Claude Desktop / Cursor)

await sdk.startMcpServer({ transport: 'stdio' });

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "toolpack": {
      "command": "node",
      "args": ["path/to/your-server.js"]
    }
  }
}

Filtering exposed tools

// Expose only filesystem and git tools
await sdk.startMcpServer({
  transport: 'http',
  port: 3000,
  expose: { categories: ['filesystem', 'version-control'] },
});

// Expose specific tools by name
await sdk.startMcpServer({
  transport: 'http',
  port: 3000,
  expose: { tools: ['fs.read_file', 'fs.write_file', 'git.commit'] },
});

Authentication

Three auth modes are supported for HTTP transport. When auth is omitted, the server accepts all requests (safe for localhost only).

Static tokens (dev / self-hosted)

await sdk.startMcpServer({
  transport: 'http',
  port: 3000,
  auth: {
    mode: 'static',
    tokens: [process.env.MCP_TOKEN!],
    // Pass multiple tokens for zero-downtime rotation
  },
});

JWT (Auth0, Supabase, Clerk)

await sdk.startMcpServer({
  transport: 'http',
  port: 3000,
  auth: {
    mode: 'jwt',
    jwksUrl: 'https://your-tenant.auth0.com/.well-known/jwks.json',
    audience: 'https://your-mcp-server.example.com',
    issuer:   'https://your-tenant.auth0.com/',
    requiredScopes: ['tools:read'],
  },
});

Custom verification

await sdk.startMcpServer({
  transport: 'http',
  port: 3000,
  auth: {
    mode: 'custom',
    verifyAccessToken: async (token) => {
      const user = await db.findByToken(token);
      if (!user) throw new Error('invalid token');
      return { token, clientId: user.id, scopes: user.scopes };
    },
  },
});

Search mode

When searchMode: true, tools/list returns only tool.search instead of all 100+ tools. MCP clients call tool.search to discover tools on demand — dramatically reducing context token usage for large tool sets.

const sdk = await Toolpack.init({
  provider: 'anthropic',
  tools: true,
  modeOverrides: {
    default: { toolSearch: { enabled: true } },
  },
});

await sdk.startMcpServer({
  transport: 'http',
  port: 3000,
  searchMode: true,
});

Add the following to your MCP client's system prompt:

This server exposes tools via tool.search. Before calling any tool, use tool.search
with a short keyword query to discover available tools. Then call the tool by name.

Exposing agents as MCP tools

Use McpChannel from @toolpack-sdk/agents to expose a Toolpack agent as an MCP tool. The agent appears in tools/list as agent.<name>.

import { McpChannel } from '@toolpack-sdk/agents';

const ch = new McpChannel();
const agent = new PrReviewerAgent({ channels: [ch] });
await agent.start();

await sdk.startMcpServer({
  transport: 'stdio',
  agents: [ch.asAgentDefinition(agent)],
});

Alternatively, use a plain object — no @toolpack-sdk/agents dependency required:

await sdk.startMcpServer({
  transport: 'stdio',
  agents: [{
    name: 'pr_reviewer',
    description: 'Reviews a pull request end-to-end.',
    inputSchema: {
      type: 'object',
      properties: { pr_url: { type: 'string' } },
      required: ['pr_url'],
    },
    invoke: async (args) => {
      const result = await prReviewer.invokeAgent({ data: args });
      return result.output;
    },
  }],
});

McpServerHandle

startMcpServer() returns a handle:

Property / Method	Description
handle.port	Bound port (HTTP only). Useful with port: 0 (OS-assigned free port).
handle.toolCount	Number of tools currently exposed.
handle.stop()	Gracefully shut down the server.

port: 0 — OS-assigned port

Pass port: 0 to let the OS choose a free port. Read the actual port from handle.port:

const handle = await sdk.startMcpServer({ transport: 'http', port: 0 });
console.log(`Listening on port ${handle.port}`);

Next Steps

• See packages/toolpack-sdk/docs/examples/mcp-server-example.ts for a full working example
• Explore the MCP specification for protocol details
• Learn about McpChannel for exposing agents over MCP
• Check out available MCP servers to use as a client