23/04/2025
MCP vs Agent-to-Agent vs Function Calling
Letโs start with the 'solutions', when to use which:
โ
Use ๐ ๐๐ฃ when you want your model to be context-aware โ knowing the user, tools, memory, rules, and task
โ
Use ๐๐๐ป๐ฐ๐๐ถ๐ผ๐ป ๐๐ฎ๐น๐น๐ถ๐ป๐ด when the model needs to do something โ search, fetch, trigger, retrieve
โ
Use ๐๐ฎ๐ ๐ฝ๐ฟ๐ผ๐๐ผ๐ฐ๐ผ๐น when your system needs multiple agents to collaborate, each with their own role and responsibility
Now, time for their stories!๐ฃ
โ ๐ ๐๐ฃ (๐ ๐ผ๐ฑ๐ฒ๐น-๐๐ผ๐ป๐๐ฒ๐
๐ ๐ฃ๐ฟ๐ผ๐๐ผ๐ฐ๐ผ๐น)
In short, itโs a way to give LLMs a structured understanding of the world around them:
who the user is, what tools are available, what memory to retain.
Itโs context-as-code, not just context-as-prompt.
(I shared more in my last post, Iโll drop the link in the comments)
But MCP is just one part of the picture.
โ ๐๐ด๐ฒ๐ป๐-๐๐ผ-๐๐ด๐ฒ๐ป๐ ๐ฃ๐ฟ๐ผ๐๐ผ๐ฐ๐ผ๐น๐
This is about how multiple agents communicate with each other, not just the user anymore.
Instead of one big model doing everything, you break the task into smaller parts handled by different agents. They take on roles, pass tasks, and coordinate to solve more complex goals.
You might have a flow like:
- Planner agent: โYou handle the research.โ
- Research agent: โHereโs what I found.โ
- Writer agent: โGreat, Iโll start drafting.โ
In most current systems, this is done through direct message passing, often one agent at a time, with fairly simple, turn-based logic.
The structure is usually custom and manually defined,
it's effective, but still early-stage.
Thatโs why more standardization is starting to emerge, to make these systems more modular and scalable.
โ ๐๐๐ป๐ฐ๐๐ถ๐ผ๐ป ๐๐ฎ๐น๐น๐ถ๐ป๐ด
This is probably the one weโre most familiar with.
Itโs when a model doesnโt just respond with text โ it actually calls a tool.
Like when it says, โLet me look that up,โ and triggers something like
search_web(query="...")
Itโs how LLMs interact with APIs, databases, calendars, emails - basically anything external.
Function calling turns LLMs from passive responders into real action-takers.
๐MCP, A2A, Functional calling...
theyโre not competing,
theyโre ๐ฏ๐๐ถ๐น๐ฑ๐ถ๐ป๐ด ๐ฏ๐น๐ผ๐ฐ๐ธ๐.
๐กAnd in practice, the most capable systems donโt choose one, they combine all three.
MCP provides the structured context,
Function Calling connects agents to real tools,
A2A protocols coordinate the work across roles.
This layered approach is what powers the next generation of intelligent systems:
context-aware, tool-using, and multi-agent by design.
__________
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