Is there support for Notifications?

[PatOConnor43]

Hey 👋

I was working on writing an MCP server that dynamically creates Resources. After these Resources are created, I send a ResourceListChanged notification to let the client know that there are new Resources. I was testing this by using the :MCPHub command and then triggering the tools from there.

It's probably possible that the UI just didn't update but I didn't see where this would be implemented in the code. I can also confirm that when I pressed r, the resources did appear.

After submitting the tool:

After pressing r to refresh:

Thanks for all the work on this project!

Links:
https://modelcontextprotocol.io/docs/concepts/resources#list-changes
https://modelcontextprotocol.io/specification/2024-11-05/basic/messages#notifications

[ravitemer]

@PatOConnor43 Thank you. It is supposed to work without "r" refreshing. I remember testing it with puppeteer and stagehand where on taking a screenshot we get the new screenshots resources. I have pointed out locations where we handle these notifications both in mcp-hub and mcphub.nvim repos.

In mcp-hub repo, we propagate notifications from MCPConnection.js to MCPHub.js to server.js

https://github.com/ravitemer/mcp-hub/blob/87e87598a982df18cb6e5d3a7bc8d866deaa86e7/src/MCPConnection.js#L239-L260

https://github.com/ravitemer/mcp-hub/blob/87e87598a982df18cb6e5d3a7bc8d866deaa86e7/src/MCPHub.js#L73-L77

https://github.com/ravitemer/mcp-hub/blob/87e87598a982df18cb6e5d3a7bc8d866deaa86e7/src/server.js#L118-L129

In mcphub.nvim plugin, we listen for resource list changed events here:

mcphub.nvim/lua/mcphub/utils/handlers.lua

Lines 65 to 83 in fec8c2d

	elseif event == constants.EventTypes.SUBSCRIPTION_EVENT then
	local is_capability_type = vim.tbl_contains({
	constants.SubscriptionTypes.TOOL_LIST_CHANGED,
	constants.SubscriptionTypes.RESOURCE_LIST_CHANGED,
	constants.SubscriptionTypes.PROMPT_LIST_CHANGED,
	}, data.type)
	if is_capability_type then
	hub:handle_capability_updates(data)
	elseif data.type == constants.SubscriptionTypes.CONFIG_CHANGED then
	if not is_ui_shown then
	local has_significant_changes = data.isSignificant == true
	if not has_significant_changes then
	vim.notify("MCP Hub Config Changed: No Significant changes found", vim.log.levels.INFO, {
	title = "MCP Hub",
	})
	end
	end
	hub:refresh_config()
	elseif data.type == constants.SubscriptionTypes.SERVERS_UPDATING then

And update the state in handle_capability_updates:

mcphub.nvim/lua/mcphub/hub.lua

Lines 794 to 828 in fec8c2d

	function MCPHub:handle_capability_updates(data)
	local type = data.type
	local server = data.server
	local map = {
	[constants.SubscriptionTypes.TOOL_LIST_CHANGED] = { "tools" },
	[constants.SubscriptionTypes.RESOURCE_LIST_CHANGED] = { "resources", "resourceTemplates" },
	[constants.SubscriptionTypes.PROMPT_LIST_CHANGED] = { "prompts" },
	}
	local fields_to_update = map[type]
	if not fields_to_update then
	log.warn("Unknown capability update type: " .. type)
	return
	end
	if not server then
	return
	end
	for _, s in ipairs(State.server_state.servers) do
	if s.name == server then
	local emit_data = {
	server = server,
	hub = self,
	}
	for _, field in ipairs(fields_to_update) do
	s.capabilities[field] = data[field] or {}
	emit_data[field] = s.capabilities[field]
	end
	State:emit(type, emit_data)
	break
	end
	end
	-- Notify subscribers of state change
	State:notify_subscribers({
	server_state = true,
	}, "server")
	end

Ideally, this part should update the UI,

mcphub.nvim/lua/mcphub/hub.lua

Lines 824 to 827 in fec8c2d

	-- Notify subscribers of state change
	State:notify_subscribers({
	server_state = true,
	}, "server")

For debugging, you can add some vim.notify statements inside the handle_capabiliy_updates function.

Please let me know your findings. I suggest you also read contributing.md for more info on dev setup.

mcphub.nvim/CONTRIBUTING.md

Lines 62 to 80 in fec8c2d

	For effective development, use a tmux-based setup with multiple panes:
	
	1. Main editor pane with mcphub.nvim code
	2. Second pane showing real-time mcp-hub logs:
	```bash
	tail -f ~/.mcp-hub/logs/mcp-hub.log
	```
	3. Third pane watching mcphub.nvim plugin logs:
	```bash
	tail -f ~/mcphub.log
	```
	This setup allows you to:
	- Monitor both frontend (plugin) and backend (mcp-hub) logs in real-time
	- See how changes affect the communication between components
	- Debug issues more effectively by correlating events

[ravitemer]

Now that I think about it, would it help if we have a dev field in a MCP server's config which takes a glob pattern and watches for any file changes in that directory to restart a particular server automatically something like a nodemon server in nodejs?

[PatOConnor43]

Thanks for all the info! Very helpful!

After fixing a separate issue in my server, I have confirmed with logging in my server that list resources is getting called after I send the notification. I think things are mostly working. At this point I think it may just be the UI not updating after list resources is called again. I added a log line here which showed this log:

SSE event: log, data: {"type":"debug","message":"Received resourcesChanged notification","data":{},"timestamp":"2025-05-26T07:24:11.326Z"}

I believe that log is coming from this line:
https://github.com/ravitemer/mcp-hub/blob/87e87598a982df18cb6e5d3a7bc8d866deaa86e7/src/MCPConnection.js#L247

I'll have to take a closer look at this in the morning. Thanks!

would it help if we have a dev field in a MCP server's config which takes a glob pattern and watches for any file changes

It was pretty simple to just toggle the server off and on to run the built server with changes. I'll leave that up to you.

[ravitemer]

It was pretty simple to just toggle the server off and on to run the built server with changes. I'll leave that up to you.

It is available with v5.5.0. More info at #141 discussion

At this point I think it may just be the UI not updating after list resources is called again. I added a log line here which showed this log:

Okay, let me test with a dev server and see what's happening exactly.

[PatOConnor43]

Short story: Good news! It works now 👍

Long story: I uninstalled mcp-hub and installed a local version to start debugging the issue. It turns out it works fine now. I believe I should have been on mcp-hub 3.2.0 but I don't see anything in your most recent release that would have fixed it. Something I did while getting the dev environment set up was kill the running mcp-hub instance so I could npm run start on the port and have Neovim connect to that.

I installed 3.2.0 recently because I updated mcp-hub.nvim but now I'm wondering if I've had an older version of the server still running. I don't know what you do to determine when you need to restart mcp-hub if the npm package is updated.

Regardless, thanks for the help debugging this!

[ravitemer]

Okay I am assuming you cloned the mcp-hub repo in order to debug the issue? If so, you should update the mcphub.nvim config to use the cloned mcp-hub like:

mcphub.setup({
	cmd = "node",
	cmdArgs = {
		"/path/to/mcp-hub/src/utils/cli.js",
	},
})

More info about this at https://ravitemer.github.io/mcphub.nvim/configuration.html#cmd-cmdargs

If cmd, cmdArgs are not specified, it uses mcp-hub binary available in your system which however should be updated when you update the mcphub.nvim plugin if you are using the correct build step like;

{
    "ravitemer/mcphub.nvim",
    dependencies = {
        "nvim-lua/plenary.nvim",
    },
    build = "npm install -g mcp-hub@latest",  -- Installs `mcp-hub` node binary globally
    config = function()
        require("mcphub").setup()
    end
}

https://ravitemer.github.io/mcphub.nvim/installation.html#default-installation

I'm wondering if I've had an older version of the server still running. I don't know what you do to determine when you need to restart mcp-hub if the npm package is updated.

You can try ps aux | grep "mcp-hub" to see the pid of the mcp-hub process.

You can also try lsof -i :37373 to see what's listening on the default port of 37373 which mcphub.nvim plugin uses.