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New in version 2.3.5 MCP servers can report progress during long-running operations. The client can receive these updates through a progress handler.

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Progress Handler

Set a progress handler when creating the client: 
from fastmcp import Client

async def my_progress_handler(
    progress: float, 
    total: float | None, 
    message: str | None
) -> None:
    if total is not None:
        percentage = (progress / total) * 100
        print(f"Progress: {percentage:.1f}% - {message or ''}")
    else:
        print(f"Progress: {progress} - {message or ''}")

client = Client(
    "my_mcp_server.py",
    progress_handler=my_progress_handler
)

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Handler Parameters

The progress handler receives three parameters:

Progress Handler Parameters

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progress
float
Current progress value
​
total
float | None
Expected total value (may be None)
​
message
str | None
Optional status message (may be None)

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Per-Call Progress Handler

Override the progress handler for specific tool calls: 
async with client:
    # Override with specific progress handler for this call
    result = await client.call_tool(
        "long_running_task", 
        {"param": "value"}, 
        progress_handler=my_progress_handler
    )