Function calling is the capability of language models to invoke external tools and APIs during conversations. It enables AI agents to take actions beyond generating text, such as querying databases, booking appointments, or processing transactions.
How does function calling work?
The language model receives descriptions of available functions including their parameters and purposes. When appropriate during conversation, the model generates a structured call to the relevant function with the necessary arguments. The system executes the function and returns results for the model to incorporate into its response.
Why does function calling matter?
Without function calling, AI agents can only converse. With it, they become capable of real work. The difference between an agent that talks about scheduling and one that actually books appointments is function calling. It bridges the gap between understanding requests and fulfilling them.
Function calling in practice
A caller asks to check their account balance. The language model recognizes this requires the check_balance function, extracts the account identifier from the conversation, and generates a function call. The system executes the query and returns $1,247.50. The model incorporates this into a natural response: “Your current balance is $1,247.50.”