Most exam guides describe this. We show it.
Scroll, and watch one tool call make the round trip the whole exam is built on.
Claude sits behind a wall.
It reads text and writes text. It can't open a file, call an API or check the weather.
Every request carries everything.
Your code packs the whole conversation and slides it in. The API remembers nothing between calls.
Claude asks. It never acts.
To get the weather it writes a tool_use block: a tool name, an input, and an id.
Your code does the work.
It calls the real API, then sends back a tool_result with the same id so Claude can match them.
It loops until Claude is done.
stop_reason: end_turn. One small field decides what your code does next, and the exam leans on it hard.