The loop

A language model does one thing. Given some text, it produces more text. It cannot search the web, read your database, or send an email.

Everything that looks like an AI doing something is this loop wrapped around that one ability.

One turn

Without tools, a generation is a single round trip. You send messages and a list of tools the model may use, the model replies with text, and you're done.

That's generateText with no tools. One request, one answer.

More than one turn

With tools, the reply might not be text. The model can instead say that it wants get_weather called with {"city": "Oslo"}. That isn't a function call. It's a message asking for one.

So the loop keeps going:

1. You send messages and tools.
2. The model replies with a tool call.
3. The SDK runs your tool and appends the result to the conversation.
4. The whole conversation, now including the call and its result, goes back.
5. The model replies, with text this time, or with another tool call.
6. Repeat from step 3 until it answers in text or a stop condition fires.

Each pass through steps 2 to 5 is a step. A run that searched twice before answering took three steps.

Why there's a limit

Nothing in this loop guarantees the model stops asking for tools. A confused model can call the same tool forever, and every step costs a request.

maxSteps is the ceiling that stops that. Most runs finish well under it. If yours regularly hits it, look at your tool descriptions before you raise the number.

stopWhen gives you finer control. End after a particular tool has been called, or on any condition you can write over the steps so far.

Why this matters

Most surprising behaviour makes sense once you can see the loop.

A tool that "didn't run" usually means the model never asked for it, which is a description problem rather than an execution one. A token bill larger than you expected usually means the loop took several steps, and every step resends the whole conversation including previous tool results. A conversation that grows alarmingly fast is usually one where tool outputs are long, since those are messages too. And a run that stopped early either hit a stop condition or ran out of steps.

Next

• Tool calling covers what the model emits and who runs it
• Generating text is the loop in code
• Agents is the loop with a fixed setup