Subscribe Functionality in Resources

[Jeomon]

Pre-submission Checklist

• I have checked that this question would not be more appropriate as an issue in a specific repository
• I have searched existing discussions and documentation for answers

Question Category

• Protocol Specification
• SDK Usage
• Server Implementation
• General Implementation
• Documentation
• Other

Your Question

Can anyone please help me to subscribe to a resource so that, as mentioned in the docs, when the resource changes, a notification is sent to notify the client that this resource is updated and fetch the new content/version of that subscribed resource? I guess this happens automatically, as mentioned in the diagram. I'm using the Python SDK.

Problem: Don't know how to implement exactly.
Client: Claude Desktop or Agno, or MCP Client

URL of the docs: https://modelcontextprotocol.io/specification/2024-11-05/server/resources

[Jeomon]

This is the implementation section of the MCP server

<Remaining code of the tool, resource and server instantiation>

@server.list_resources()
async def list_resources()->list[Resource]:
return [Resource(uri=AnyUrl(view.uri),name=resource.name,description=resource.doc,mime_type=view.mime_type) for resource,view in zip(resources,resources_view)]

@server.read_resource()
async def read_resource(uri:AnyUrl)->str|bytes:
    if uri not in resources_registry:
        return uri
    resource:Callable=resources_registry.get(uri)
    resource_response=await resource()
    return resource_response

@server.list_tools()
async def list_tools()->list[Tool]:
    return [Tool(name=tool.__name__,description=tool.__doc__,inputSchema=view.model_json_schema()) for (tool,view) in zip(tools,tools_view)]

@server.call_tool()
async def call_tool(name:str,parameters:dict[str,Any]|None)->list[TextContent|ImageContent|EmbeddedResource]:
    try:
        if not parameters:
            parameters={}
        if name not in tools_registry:
            return [TextContent(type='text',text=f'Tool {name} not found.')]
        tool:Callable=tools_registry.get(name)
        tool_response=await tool(**parameters)
        return [TextContent(type='text',text=tool_response)]
    except Exception as e:
        return [TextContent(type='text',text=f'Error: {e}')]

async with stdio_server() as (read_stream, write_stream):
    initialization_options=server.create_initialization_options(notification_options=NotificationOptions(resources_changed=True),experimental_capabilities={"resources": {"subscribe": True}})
    await server.run(read_stream,write_stream,initialization_options=initialization_options)

[hesreallyhim]

Pre-submission Checklist

• I have checked that this question would not be more appropriate as an issue in a specific repository
• I have searched existing discussions and documentation for answers

Question Category

• Protocol Specification
• SDK Usage
• Server Implementation
• General Implementation
• Documentation
• Other

Your Question

Can anyone please help me to subscribe to a resource so that, as mentioned in the docs, when the resource changes, a notification is sent to notify the client that this resource is updated and fetch the new content/version of that subscribed resource? I guess this happens automatically, as mentioned in the diagram. I'm using the Python SDK.

Problem: Don't know how to implement exactly. Client: Claude Desktop or Agno, or MCP Client

URL of the docs: https://modelcontextprotocol.io/specification/2024-11-05/server/resources

Most clients just don't support this, even Claude I think. Inspector does thouugh.

[hesreallyhim]

Can anyone please help me to subscribe to a resource so that, as mentioned in the docs, when the resource changes, a notification is sent to notify the client that this resource is updated and fetch the new content/version of that subscribed resource? I guess this happens automatically, as mentioned in the diagram. I'm using the Python SDK.

It doesn't happen automatically. Clients send resource-update-subscription-"requests" to server to let them know "hey I want to know if this resource changes" - server is free to do anything, or nothing - if they support it, they can then start sending "resources/updated" notifications to the client when the resource is updated - then the client knows the resource has changed and it can read it again.

[Jeomon]

Does Claude's desktop have a sending request to the server to see whether the resource has been updated through notification

[hesreallyhim]

i haven't tested it with Claude Dekstop yet, but i am building an MCP server with resource subscriptions and update notifications - I have heard that Claude Desktop does not support this (Claude told me so itself) - but Inspector does, and I've seen the notifications coming through. It's not trivial to implement though, e.g. I used lowlevel server I don't think FastMCP does this but I might be wrong. This is the message flow:

https://modelcontextprotocol.io/specification/2025-03-26/server/resources#message-flow

Unfortunately, most of the it is totally optional - the server is not REQUIRED to do anything, so I think very few servers/clients support this, but Inspector does. There's even a built-in "Subscribe" button that will appear if you do "List Resources" and then click the Resource, as long as the server has announced during the initialization exchange that it provides this capability.

[Jeomon]

Got it, I will check out with in the inspector and yes the subscription is not available in FastMCP but in the Server

https://github.com/CursorTouch/Windows-MCP
The point was here I wish I want to supply the state as a resource and when changes to the client take that updated state

Thank you.

[hesreallyhim]

yeah totally, I am trying to build something like this too... It seems to me a lot of people are asking about this topic, since there seem to be a lot of use value. FWIW, the "update" notification is not "supposed" to actually tell the client what the update is - the message flow is that it notifies the client that the client should then read the resource again... but IMO this is pointless and you can leverage the meta field in the notification to send the client the information, even if the protocol thinks it's not what it's "supposed" to do.