Extend Progress message to return interim tool results #1150

Pre-submission Checklist

• I have verified this would not be more appropriate as a feature request in a specific repository
• I have searched existing discussions to avoid duplicates

Your Idea

Hi Team,

We came across this use case while implementing a MCP tool. Please review and let me know your thoughts. Thanks!

What problem does it solve?

Use case:
Let's say we have a MCP tool that executes a task that runs for a few minutes. The tool provides the outputs in a staged manner for better real-time user experience. For example, the tool sends the result as section-1, section-2, section-3 etc..

Currently, MCP allows progress updates to be sent via Progress message. This progress message isn't considered to
be part of the task result.

Who could benefit from this?

End users interacting with AI Assistants that leverage long-running MCP tools will get quicker interim task results instead of task progress messages.

How might it be implemented?

Proposal:
Extend the Progress message to contain an interim result.

Example:

{
  "jsonrpc": "2.0",
  "method": "notifications/progress",
  "params": {
    "progressToken": "abc123",
    "progress": 30,
    "result": {
       "content": [
          {
              "type": "text",
              "text": "..."
          }
      ]
      "structuredContent": {
         ...
      }
  }
 }
}

The final JSON-RPC response will contain the the last section of the result in this scenario.

Scope

• Protocol Specification
• SDK Features
• Documentation
• Developer Experience
• Other