GLOSSARY
Function Calling
The model emits a structured call to a tool you defined — search, calendar, database — instead of pretending it did the work in prose.
Function calling (often the same idea as tool calling) is how chat models leave the text box: you declare a schema, the model fills the arguments, your runtime executes the function, and the result goes back into the conversation. Weather, tickets, SQL, browser actions — none of that is generation; it is a side effect the model requested.
The hard parts are the schema and the loop. Vague tool descriptions produce junk arguments; missing error channels make agents retry forever. Structured output and function calling are cousins: both demand the model speak a contract, not a paragraph. Every serious agent stack is this loop with retries.