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by tptacek 244 days ago
What can I do with MCP that I can't do with the function calling interface in the OpenAI Responses API? Besides, obviously, grafting function calls into agents I didn't write; we all understand that's the value prop of MCP. But you're suggesting it's more than that. Fill in the blanks for us.
2 comments
didibus 243 days ago
The MCP can expose a list of tools, but also a list of prompt templates, a list of resources, it can ask the client to run something through the LLM (called sampling), and it can provide rules for when to follow up with questions.

But you can do all that yourself if you're building your own agent and directly calling a model. But if you want to be able to provide behavior to any agent, that's where MCP comes in.

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brazukadev 244 days ago
The LLM can only use MCP tools, but the Client you use the model can access resources, prompts, elicitation and sampling, which are tools to help with querying the model. So one MCP server that implements some or all these features can act as an agent for the LLM dispatching tasks IF the client is also an MCP host/client.
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ming030890 244 days ago
But most of these can really be just a tool.

For example, A resource can be just a getter tool, like getFile.

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brazukadev 243 days ago
MCP is a protocol, a proposal on standardizing how to do things so we can reuse tools. Whatever thing you want to do with MCP you can do without MCP, that is obvious. But when lots of people agree to write and consume using the same protocol there is a big productivity rise.
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didibus 243 days ago
Resources could be a tool like list resources, but exposing them as resources means in the client you can show the user the list of resources, and the client can choose to include their descriptions in the context without the model choosing to do so for example.
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tptacek 244 days ago
Right. My understanding of these APIs and model capabilities is imperfect, but at the level I interact with them at, there are only two things: prompts (more broadly: context chunks) and tool calls. I don't see how MCP could meaningfully expand that; it seems like anything I could do with MCP, I could do with context chunks and tool calls --- perhaps better, because I'd have finer-grained control of both security and of context management.
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