tool use

Tool use is the capability of a language model to invoke external functions or services during generation and to integrate their outputs into its ongoing reasoning and responses.

In practice, applications expose tools through structured interfaces, run the requested operations in external systems, and then feed the results back to the model so it can decide what to do next.

Common tools include retrieval or web search, code execution environments, calculators, and domain-specific APIs. These extend a model beyond its fixed training data and allow it to query live information or perform real actions in the outside world.

Research on tool use has produced prompting and training strategies that interleave reasoning with actions, route requests to specialized components, and help models learn when and how to issue API calls. This capability underpins patterns like retrieval-augmented generation (RAG) where retrieval is treated as a tool.