Function Calling: The LLM Picks a Predefined Function
~12 min read
Function calling lets the LLM decide which developer-defined function to invoke based on the user's prompt. It predates MCP and still has real limitations: the M×N integration problem, tight app-specific coupling, and manual update propagation.
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Key points
- •Function calling lets the LLM decide which developer-defined function to call, based on interpreting the user's input
- •It predates MCP and is genuinely useful — it's what first let LLMs take real actions beyond text generation
- •Limitation 1: the M×N integration problem — M AI apps × N functions can require M×N distinct integrations
- •Limitation 2: functions are tightly coupled to specific applications, making reuse across systems hard
- •Limitation 3: any function change requires manual updates across every instance using it, same as traditional APIs