Messages changedspecification/2024-11-05/basic/messages

Nearest release: v2.1.246, published 8 hours before this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.

Recorded here 26 Aug 2026 03:37 UTC

Lines+65added

Lines−0removed

From line — no hunk to open at

First seen 26 Aug 2026 this site's first read of the page

Recorded edits1to this page, all time

# Messages ## Requests ## Responses ## Notifications

The whole hunk

65 lines, new page

lines

A whole new page. There's nothing to diff it against, so here is what it says.

# Messages

All messages in MCP **MUST** follow the
[JSON-RPC 2.0](https://www.jsonrpc.org/specification) specification. The protocol defines
three types of messages:

## Requests

Requests are sent from the client to the server or vice versa.

```typescript theme={null}
{
  jsonrpc: "2.0";
  id: string | number;
  method: string;
  params?: {
    [key: string]: unknown;
  };
}
```

* Requests **MUST** include a string or integer ID.
* Unlike base JSON-RPC, the ID **MUST NOT** be `null`.
* The request ID **MUST NOT** have been previously used by the requestor within the same
  session.

## Responses

Responses are sent in reply to requests.

```typescript theme={null}
{
  jsonrpc: "2.0";
  id: string | number;
  result?: {
    [key: string]: unknown;
  }
  error?: {
    code: number;
    message: string;
    data?: unknown;
  }
}
```

* Responses **MUST** include the same ID as the request they correspond to.
* Either a `result` or an `error` **MUST** be set. A response **MUST NOT** set both.
* Error codes **MUST** be integers.

## Notifications

Notifications are sent from the client to the server or vice versa. They do not expect a
response.

```typescript theme={null}
{
  jsonrpc: "2.0";
  method: string;
  params?: {
    [key: string]: unknown;
  };
}
```

* Notifications **MUST NOT** include an ID.