The core operating pattern of AI Agents: perceive environment → decide → execute action → observe results → decide again, cycling until the task is complete. The key mechanism that upgrades AI from "one question, one answer" to "autonomously completing multi-step tasks."

The capability that lets Claude call external functions, APIs, or programs to perform real operations. With Tool Use, Claude doesn't just generate text — it can search the web, run calculations, query databases, and manipulate files, turning "saying it can do" into "actually doing it."