Last updated: 2026-05-11
MCP vs Function Calling
Function calling is usually app-local. MCP is a reusable protocol boundary for tools and context across clients.
Quick recommendation: Use function calling for one product and one agent runtime. Use MCP when tool access should be shared, discoverable, and governed across clients.
Choose the first option when
- One app owns the model, tool schema, and backend.
- The tool set is small and product-specific.
- You want the fewest moving parts.
Choose the second option when
- Multiple clients need the same tools.
- Tool providers and agent clients are owned by different teams.
- You need a protocol boundary with discovery and resources.
Feature comparison
| Scope | App-local tool calls | Cross-client tool and context protocol |
|---|---|---|
| Governance | Usually enforced in application code | Can be centralized at the server boundary |
| Complexity | Lower for one app | Better once integrations repeat |
Developer experience
Function calling is faster to ship. MCP pays off when tool ownership, client diversity, or reuse becomes the bottleneck.
Final recommendation
Start with function calling for a narrow app. Move to MCP when the tool surface becomes a product of its own.