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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.

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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
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