ChatGPT's ability to search the web, run code, and generate images are all powered by tool use — the LLM calls specialized functions and incorporates their results into its response.
Watch how each step unfolds below.
The Pattern: Observe → Reason → Act → Observe Result → Respond
This is the ReAct patternat its core. Without tools, the LLM can only answer from its training data — it would have to guess or say "I don't know." Tool use lets the LLM reach out to the real world and ground its response in actual, fresh data.
User Message
LLM Thinking
Tool Call
Tool Result
Final Response