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110 changes: 71 additions & 39 deletions README.md
Original file line number Diff line number Diff line change
Expand Up @@ -28,7 +28,9 @@
This extension provides a plug-and-play integration between LoopBack4 applications and the Model Context Protocol (MCP) specification.

Its purpose is to enable LoopBack APIs, services, and business logic to be exposed as MCP Tools, allowing external MCP clients (such as LLMs, agents, or MCP-compatible apps) to discover and execute server-defined operations.

### Key Features

- Automatic MCP Tool Discovery :-
The extension scans your application at boot time and automatically registers all methods decorated with the custom @mcpTool() decorator.

Expand All @@ -38,16 +40,35 @@ Its purpose is to enable LoopBack APIs, services, and business logic to be expos
A dedicated `McpToolRegistry` service maintains all discovered tool metadata,their handlers and execution context.

A `McpToolRegistryBootObserver` ensures that registration happens only after the application has fully booted.

## Installation

```sh
npm install loopback4-mcp
```
Then register the component inside your `application.ts`.

## Basic Usage

Configure and load `McpComponent` in the application constructor
as shown below.

```ts
this.component(McpComponent);
import {McpComponent} from 'loopback4-mcp';

export class MyApplication extends BootMixin(
ServiceMixin(RepositoryMixin(RestApplication)),
) {
constructor(options: ApplicationConfig = {}) {
super();
this.component(McpComponent);
}
}
```
## Usage

Add the `@mcpTool()` decorator to any controller in your application.

All MCP tool methods must use LoopBack `@param` decorators to define their input parameters.If `@param` decorators are missing, the MCP tool will fail.

```ts
@mcpTool({
name: 'create-user',
Expand All @@ -57,47 +78,58 @@ Add the `@mcpTool()` decorator to any controller in your application.
name: z.string(),
},
})
async createUser(args: {email: string; name: string}) {
return {message: `User ${args.name} created`};
async createUser(
@param.query.string('email') email: string,
@param.query.string('name') name: string,
) {
return {message: `User ${name} created`};
}
```

This decorator accepts a total of five fields, out of which `name` and `description` are mandatory and `schema`,`preHook` and `postHook` are optional enhancements.

The schema field allows defining a Zod-based validation schema for tool input parameters, while preHook and postHook enable execution of custom logic before and after the tool handler runs.

### Mcp Hook Usage Details
To use hooks with MCP tools, follow the provider-based approach:

Step 1: Create a hook provider:
```ts
// src/providers/my-hook.provider.ts
export class MyHookProvider implements Provider<McpHookFunction> {
constructor(@inject(LOGGER.LOGGER_INJECT) private logger: ILogger) {}
value(): McpHookFunction {
return async (context: McpHookContext) => {
this.logger.info(`Hook executed for tool: ${context.toolName}`);
};
}
}
```
Step 2: Add binding key to McpHookBindings:
```ts
// src/keys.ts
export namespace McpHookBindings {
export const MY_HOOK = BindingKey.create<McpHookFunction>('hooks.mcp.myHook');
## Mcp Hook Usage Details

To use hooks with MCP tools, follow the provider-based approach:

Step 1: Create a hook provider:

```ts
// src/providers/my-hook.provider.ts
export class MyHookProvider implements Provider<McpHookFunction> {
constructor(@inject(LOGGER.LOGGER_INJECT) private logger: ILogger) {}
value(): McpHookFunction {
return async (context: McpHookContext) => {
this.logger.info(`Hook executed for tool: ${context.toolName}`);
};
}
```
Step 3: Bind provider in `application.ts`:
```typescript
this.bind(McpHookBindings.MY_HOOK).toProvider(MyHookProvider);
```
Step 4: Use in decorator:
```ts
@mcpTool({
name: 'my-tool',
description: 'my-description'
preHookBinding: McpHookBindings.MY_HOOK,
postHookBinding: 'hooks.mcp.myOtherHook' // or string binding key
})
```
}
```

Step 2: Add binding key to McpHookBindings:

```ts
// src/keys.ts
export namespace McpHookBindings {
export const MY_HOOK = BindingKey.create<McpHookFunction>('hooks.mcp.myHook');
}
```

Step 3: Bind provider in `application.ts`:

```typescript
this.bind(McpHookBindings.MY_HOOK).toProvider(MyHookProvider);
```

Step 4: Use in decorator:

```ts
@mcpTool({
name: 'my-tool',
description: 'my-description'
preHookBinding: McpHookBindings.MY_HOOK,
postHookBinding: 'hooks.mcp.myOtherHook' // or string binding key
})
```
2 changes: 2 additions & 0 deletions src/services/mcp-tool-registry.service.ts
Original file line number Diff line number Diff line change
Expand Up @@ -51,6 +51,7 @@ export class McpToolRegistry {
const processedTools: McpToolMetadata[] = [];
const prototype = targetClass.prototype;

// Retrieve all tool metadata that was stored earlier by @mcpTool decorator
const allTools = MetadataInspector.getAllMethodMetadata<McpToolMetadata>(
MCP_TOOL_METADATA_KEY,
prototype,
Expand Down Expand Up @@ -116,6 +117,7 @@ export class McpToolRegistry {
return [];
}

// extracts all methods decroated with @mcpTool
const tools = this.getMcpToolsFromClass(controllerClass);

if (tools.length === 0) return [];
Expand Down