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# `x402/mcp.mpp` \[Add MPP to an x402 MCP tool]

Wraps an official x402 MCP tool handler so calls can pay through MPP or x402 metadata.

## Usage

```ts [server.ts]
import { x402ResourceServer } from '@x402/core/server'
import { mpp } from 'mppx/x402/mcp'

const paid = mpp(resourceServer, {
  accepts,
  resource: {
    description: 'Premium search',
    url: 'mcp://tool/search',
  },
  secretKey: process.env.MPP_SECRET_KEY!,
})

const search = paid(async ({ query }: { query: string }) => ({
  content: [{ text: `result:${query}`, type: 'text' }],
}))
```

The resource URL must use the canonical `mcp://tool/{toolName}` shape without another path segment, query, or fragment. An unpaid call returns one `-32042` MCP payment error containing both MPP Challenges and the x402 payment requirements. A rejected MPP Credential returns `-32043` with a replacement Challenge.

x402 Credentials and lifecycle hooks stay with `@x402/mcp`. MPP source-chain EVM Credentials reuse the x402 resource server for verification and settlement; x402-only hooks run only for x402 calls.

## Return type

```ts
type ReturnType = <arguments_ extends Record<string, unknown>>(
  handler: PaymentWrappedHandler<arguments_>,
) => MCPToolCallback<arguments_>
```

## Parameters

### config

* **Type:** `Config`

Existing x402 MCP payment settings plus the MPP realm and secret. `resource.url` must match the canonical tool URL described above; `resource.description` and `resource.mimeType` remain optional. `secretKey` must contain at least 32 bytes.

### resourceServer

* **Type:** `x402ResourceServer`

Existing x402 resource server used for requirement metadata, verification, and settlement.