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.

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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.

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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

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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