What is tool use?
Tool use — also called function calling — is the ability of a language model to invoke external functions during a conversation. Instead of generating text, the model outputs a structured function call with parameters. Your application executes the function and returns the result. The model then continues generating based on that result.
This is how AI applications interact with databases, APIs, file systems, and other software. The model decides which tool to use and with what parameters. Your code executes the actual operation.
Why it matters
Without tool use, a model can only generate text. With tool use, it can query databases, send emails, create records, and trigger workflows. This is the feature that separates chatbots from agents. sourc.dev tracks tool use support as a capability flag on every model entity.