Techniques & Methods
Tool Use in plain English.
Also known as: function calling,tool calling
The one-sentence version
How AI models call external tools — search, code execution, APIs — to do real work.
Tool use (also called function calling) is how modern AI models call external tools to do things they cannot do alone. The model decides "I need to search the web" or "I need to run this Python code" or "I need to call the weather API" — and generates a structured request to invoke that tool. The tool runs, returns results, and the model continues. Tool use is what enables agentic AI: it is the difference between a chatbot and an actual assistant. Reliability has been the limiting factor — Claude Opus 4.8 reached 96% tool-use reliability in mid-2026, a meaningful step up from 89% in Opus 4.7.