NestJS MCP Server Module

A NestJS module to effortlessly expose tools, resources, and prompts for AI, from your NestJS applications using the Model Context Protocol (MCP).

With @rekog/mcp-nest you define tools, resources, and prompts in a way that's familiar in NestJS and leverage the full power of dependency injection to utilize your existing codebase in building complex enterprise ready MCP servers.

Features

• 🚀 Support for all Transport Types:
  • Streamable HTTP
  • HTTP+SSE
  • STDIO
• 🔍 Automatic tool, resource, and prompt discovery and registration
• 💯 Zod-based tool call validation
• 📊 Progress notifications
• 🔒 Guard-based authentication
• 🌐 Access to HTTP Request information within MCP Resources (Tools, Resources, Prompts)

Installation

npm install @rekog/mcp-nest @modelcontextprotocol/sdk zod

Quick Start

1. Import Module

// app.module.ts
import { Module } from '@nestjs/common';
import { McpModule } from '@rekog/mcp-nest';
import { GreetingTool } from './greeting.tool';

@Module({
  imports: [
    McpModule.forRoot({
      name: 'my-mcp-server',
      version: '1.0.0',
    }),
  ],
  providers: [GreetingTool],
})
export class AppModule {}

2. Define Tools and Resource

// greeting.tool.ts
import type { Request } from 'express';
import { Injectable } from '@nestjs/common';
import { Tool, Resource, Context } from '@rekog/mcp-nest';
import { z } from 'zod';
import { Progress } from '@modelcontextprotocol/sdk/types';

@Injectable()
export class GreetingTool {
  constructor() {}

  @Tool({
    name: 'hello-world',
    description:
      'Returns a greeting and simulates a long operation with progress updates',
    parameters: z.object({
      name: z.string().default('World'),
    }),
  })
  async sayHello({ name }, context: Context, request: Request) {
    const userAgent = request.get('user-agent') || 'Unknown';
    const greeting = `Hello, ${name}! Your user agent is: ${userAgent}`;
    const totalSteps = 5;
    for (let i = 0; i < totalSteps; i++) {
      await new Promise((resolve) => setTimeout(resolve, 100));

      // Send a progress update.
      await context.reportProgress({
        progress: (i + 1) * 20,
        total: 100,
      } as Progress);
    }

    return {
      content: [{ type: 'text', text: greeting }],
    };
  }

  @Resource({
    uri: 'mcp://hello-world/{userName}',
    name: 'Hello World',
    description: 'A simple greeting resource',
    mimeType: 'text/plain',
  })
  // Different from the SDK, we put the parameters and URI in the same object.
  async getCurrentSchema({ uri, userName }) {
    return {
      content: [
        {
          uri,
          text: `User is ${userName}`,
          mimeType: 'text/plain',
        },
      ],
    };
  }
}

You are done!

[!TIP] The above example shows how HTTP Request headers are accessed within MCP Tools. This is useful for identifying users, adding client-specific logic, and many other use cases. For more examples, see the Authentication Tests.

Quick Start for STDIO

The main difference is that you need to provide the transport option when importing the module.

McpModule.forRoot({
  name: 'playground-stdio-server',
  version: '0.0.1',
  transport: McpTransportType.STDIO,
});

The rest is the same, you can define tools, resources, and prompts as usual. An example of a standalone NestJS application using the STDIO transport is the following:

async function bootstrap() {
  const app = await NestFactory.createApplicationContext(AppModule, {
    logger: false,
  });
  return app.close();
}

void bootstrap();

Next, you can use the MCP server with an MCP Stdio Client (see example), or after building your project you can use it with the following MCP Client configuration:

{
  "mcpServers": {
    "greeting": {
      "command": "node",
      "args": [
        "<path to dist js file>",
      ]
    }
  }
}

API Endpoints

HTTP+SSE transport exposes two endpoints:

• GET /sse: SSE connection endpoint (Protected by guards if configured)
• POST /messages: Tool execution endpoint (Protected by guards if configured)

Streamable HTTP transport exposes the following endpoints:

• POST /mcp: Main endpoint for all MCP operations (tool execution, resource access, etc.). In stateful mode, this creates and maintains sessions.
• GET /mcp: Establishes Server-Sent Events (SSE) streams for real-time updates and progress notifications. Only available in stateful mode.
• DELETE /mcp: Terminates MCP sessions. Only available in stateful mode.

Tips

It's possible to use the module with global prefix, but the recommended way is to exclude those endpoints with:

app.setGlobalPrefix('/api', { exclude: ['sse', 'messages', 'mcp'] });

Authentication

You can secure your MCP endpoints using standard NestJS Guards.

1. Create a Guard

Implement the CanActivate interface. The guard should handle request validation (e.g., checking JWTs, API keys) and optionally attach user information to the request object.

Nothing special, check the NestJS documentation for more details.

2. Apply the Guard

Pass your guard(s) to the McpModule.forRoot configuration. The guard(s) will be applied to both the /sse and /messages endpoints.

// app.module.ts
import { Module } from '@nestjs/common';
import { McpModule } from '@rekog/mcp-nest';
import { GreetingTool } from './greeting.tool';
import { AuthGuard } from './auth.guard';

@Module({
  imports: [
    McpModule.forRoot({
      name: 'my-mcp-server',
      version: '1.0.0',
      guards: [AuthGuard], // Apply the guard here
    }),
  ],
  providers: [GreetingTool, AuthGuard], // Ensure the Guard is also provided
})
export class AppModule {}

That's it! The rest is the same as NestJS Guards.

Playground

The playground directory contains examples to quickly test MCP and @rekog/mcp-nest features. Refer to the playground/README.md for more details.

Configuration

The McpModule.forRoot() method accepts an McpOptions object to configure the server. Here are the available options:

Option	Description	Default
name	Required. The name of your MCP server.	-
version	Required. The version of your MCP server.	-
capabilities	Optional MCP server capabilities to advertise. See @modelcontextprotocol/sdk.	undefined
instructions	Optional instructions for the client on how to interact with the server.	undefined
transport	Specifies the transport type(s) to enable.	[McpTransportType.SSE, McpTransportType.STREAMABLE_HTTP, McpTransportType.STDIO]
sseEndpoint	The endpoint path for the SSE connection (used with SSE transport).	'sse'
messagesEndpoint	The endpoint path for sending messages (used with SSE transport).	'messages'
mcpEndpoint	The base endpoint path for MCP operations (used with STREAMABLE_HTTP transport).	'mcp'
guards	An array of NestJS Guards to apply to the MCP endpoints for authentication/authorization.	[]
decorators	An array of NestJS Class Decorators to apply to the generated MCP controllers.	[]
sse	Configuration specific to the SSE transport.	{ pingEnabled: true, pingIntervalMs: 30000 }
sse.pingEnabled	Whether to enable periodic SSE ping messages to keep the connection alive.	true
sse.pingIntervalMs	The interval (in milliseconds) for sending SSE ping messages.	30000
streamableHttp	Configuration specific to the STREAMABLE_HTTP transport.	{ enableJsonResponse: true, sessionIdGenerator: undefined, statelessMode: true }
streamableHttp.enableJsonResponse	If true, allows the /mcp endpoint to return JSON responses for non-streaming requests (like listTools).	true
streamableHttp.sessionIdGenerator	A function to generate unique session IDs when running in stateful mode. Required if statelessMode is false.	undefined
streamableHttp.statelessMode	If true, the STREAMABLE_HTTP transport operates statelessly (no sessions). If false, it operates statefully, requiring a sessionIdGenerator.	true