Progress changedspecification/2024-11-05/basic/utilities/progress

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

# Progress

The Model Context Protocol (MCP) supports optional progress tracking for long-running
operations through notification messages. Either side can send progress notifications to
provide updates about operation status.

## Progress Flow

When a party wants to *receive* progress updates for a request, it includes a
`progressToken` in the request metadata.

* Progress tokens **MUST** be a string or integer value
* Progress tokens can be chosen by the sender using any means, but **MUST** be unique
  across all active requests.

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "some_method",
  "params": {
    "_meta": {
      "progressToken": "abc123"
    }
  }
}
```

The receiver **MAY** then send progress notifications containing:

* The original progress token
* The current progress value so far
* An optional "total" value

```json theme={null}
{
  "jsonrpc": "2.0",
  "method": "notifications/progress",
  "params": {
    "progressToken": "abc123",
    "progress": 50,
    "total": 100
  }
}
```

* The `progress` value **MUST** increase with each notification, even if the total is
  unknown.
* The `progress` and the `total` values **MAY** be floating point.

## Behavior Requirements

1. Progress notifications **MUST** only reference tokens that:
   * Were provided in an active request
   * Are associated with an in-progress operation

2. Receivers of progress requests **MAY**:
   * Choose not to send any progress notifications
   * Send notifications at whatever frequency they deem appropriate
   * Omit the total value if unknown

```mermaid theme={null}
sequenceDiagram
    participant Sender
    participant Receiver

    Note over Sender,Receiver: Request with progress token
    Sender->>Receiver: Method request with progressToken

    Note over Sender,Receiver: Progress updates
    loop Progress Updates
        Receiver-->>Sender: Progress notification (0.2/1.0)
        Receiver-->>Sender: Progress notification (0.6/1.0)
        Receiver-->>Sender: Progress notification (1.0/1.0)
    end

    Note over Sender,Receiver: Operation complete
    Receiver->>Sender: Method response
```

## Implementation Notes

* Senders and receivers **SHOULD** track active progress tokens
* Both parties **SHOULD** implement rate limiting to prevent flooding
* Progress notifications **MUST** stop after completion

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