MCP vs function calling
These are often framed as competitors but operate at different layers. Function calling is how a model requests a tool; MCP is a standard protocol for exposing tools and data to any model or client.
At a glance
MCP
- What it is
- A protocol for exposing tools/data
- Scope
- Cross-tool, cross-client standard
- Reuse
- One server, many agents/clients
Function calling
- What it is
- A model capability to request a tool
- Scope
- Per-app tool definitions
- Reuse
- Re-defined per application
Full comparison
| MCP | Function calling | |
|---|---|---|
| What it is | A protocol for exposing tools/data | A model capability to request a tool |
| Scope | Cross-tool, cross-client standard | Per-app tool definitions |
| Reuse | One server, many agents/clients | Re-defined per application |
| Auth & audit | Built into a well-designed server | Up to each app |
| Best for | Sharing internal systems with agents | App-specific tool calls |
Which should you choose?
They work together: a model uses function calling to invoke tools, and MCP standardizes how those tools are exposed so one server serves many agents and clients. For internal systems many teams use, MCP is the reusable, auditable layer.
Frequently asked questions
What's the difference between MCP and Function calling?
These are often framed as competitors but operate at different layers. Function calling is how a model requests a tool; MCP is a standard protocol for exposing tools and data to any model or client.
Which should I choose, MCP or Function calling?
They work together: a model uses function calling to invoke tools, and MCP standardizes how those tools are exposed so one server serves many agents and clients. For internal systems many teams use, MCP is the reusable, auditable layer.