Specification
Specification (Draft)
Base Protocol
Utilities
Progress

Progress

Protocol Revision: draft

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.
{
  "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
  • An optional “message” value
{
  "jsonrpc": "2.0",
  "method": "notifications/progress",
  "params": {
    "progressToken": "abc123",
    "progress": 50,
    "total": 100,
    "message": "Reticulating splines..."
  }
}
  • The progress value MUST increase with each notification, even if the total is unknown.
  • The progress and the total values MAY be floating point.
  • The message field SHOULD provide relevant human readable progress information.

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
  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
Cancellation