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# NestJS MCP Server Module
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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
```bash
npm install @rekog/mcp-nest @modelcontextprotocol/sdk zod
```
## Quick Start
### 1. Import Module
```typescript
// 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
```typescript
// 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](./tests/mcp-tool-auth.e2e.spec.ts).
## Quick Start for STDIO
The main difference is that you need to provide the `transport` option when importing the module.
```typescript
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:
```typescript
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](playground/clients/stdio-client.ts)), or after building your project you can use it with the following MCP Client configuration:
```json
{
"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:
```typescript
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.
```typescript
// 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`](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](https://www.npmjs.com/package/@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'` |
| `apiPrefix` | A prefix for all MCP endpoints. Useful if integrating into an existing application. | `''` |
| `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` |
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