Decision Matrix: When to Use Each
~12 min read
A concrete decision guide across all three: traditional APIs for general software-to-software integration, function calling for a simple single-app tool integration, and MCP for multi-tool, multi-app AI systems that need to discover and adapt dynamically.
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Key points
- •Traditional APIs: right for general software-to-software integration where AI/LLM decision-making isn't actually involved
- •Function calling: right for a small, stable tool set used by a single application, with no need for cross-app reuse or dynamic discovery
- •MCP: right for multi-tool, potentially multi-application AI systems where tools/interfaces are expected to evolve
- •MCP's two-way primitives (sampling, roots, elicitation) are something function calling structurally cannot provide
- •The choice isn't always MCP just because it's newest — match the tool to the actual integration's scale and evolution needs