[hobofan]

I am a pretty big proponent of MCP, and I think this at least for now is not a move in a good direction.

The whole surface of the MCP specification is already pretty big, and barely any server implements anything beyond the core parts.

With elicitation there was already a lightweight version of this in place in the standard, and I'm not sure I've ever encountered a server or client implementation of it in the wild, and elicitation is an order of magnitude simpler to integrate on a conceptional level.

I fear that this has a significant risk of splintering the MCP ecosystem further (it's already pretty strained due to the transport protocol iterations), and there isn't really a reason to create a official extension (yet), that may worst case also require multiple iterations to get things right.

[somnium_sn]

All it means that there is a common place and a recommendation that if you care as a client implementor (e.g. postman, chatgpt and others do), there is a spot to look for a generally accepted way of how to do that instead of increasing amount of proprietary extensions on top of MCP.

[hobofan]

> there is a spot to look for a generally accepted way of how to do that

I think MCP-UI in it's current state can fill that role very well, and that's not the only lens with which to view a SEP like this.

From what I can tell the main thing that this SEP does is put the official blessing of the MCP project on the existing underlying protocol that MCP-UI is already using. I think the better way would be to let MCP-UI and competing implementations cook for a little bit longer, rather than trying to get an officially sanctioned extension out the door and then iterate on that, which will cause a lot more churn.

For a non-trivial feature like this, I would expect an SEP that highlights more alternative usage scenarios and potentially operates on a more technology agonistic layer (e.g. it's very JS+iframe bound, so what about mobile or terminal UIs?), similar to the main MCP spec. Especially given the backdrop of the main MCP specification, which feels much more well-rounded and throughly considered (though in a few areas still incomplete), this SEP does not seem to meet the same bar.

Reading that from the perspective of someone that builds a LLM Chat UI[0] (and aims to be able to maintain that long-term) that heavily builds on MCP as an interoperability concept, reading what is proposed here and seeing how prescriptive it is in many aspects does not spark a lot of joy.

[0]: https://erato.chat

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EDIT: From what I can tell I'm replying to one of the co-creators of MCP. So let me just ask quite directly: Do you think that the risk of proprietary sprawl in terms of MCP-UI alternatives is currently greater than prematurely standardizing a potentially incomplete version?

[somnium_sn]

I appreciate the take. I can certainly see your position.

In my mind what we are doing is building a common place to evolve the pattern. I wouldn’t really call it “standardize”, since in the end in this space adoption matters. (Writing a standard is worth nothing if nobody is using it). I expect MCP apps to evolve and iterate independent from the main spec for a while. You are right, it’s early and premature to say “this is done”. That’s the goal with extensions.

I do believe that I rather have commonalities between a Claude.ai and a ChatGPT as a developer (not sure that’s true if I was mostly looking at it from a product perspective). I also think you will see chat providers iterate on top of it, and mcp apps is more a common core than the full thing one can use on every platform.