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Lesson 1 of 5 · 6 min read · Beginner

What an agent is: a loop that reads, decides and acts

A chatbot answers once. An agent reads the situation, decides on an action, acts, reads the result and goes round again until the job is done or something stops it. This lesson makes that loop concrete with one narrated run.

In this lesson you will

  • Describe the read, decide, act loop in your own words
  • Tell a chatbot answer from an agent run by looking at what it did
  • Recognise the two things an agent needs that a chatbot does not: tools and a stop rule

You type a question into a chatbot and it answers. Once. If the answer needs something the model does not have (today's price, your calendar, the contents of a file), it either guesses or tells you it cannot. An agent is the same model with two additions: tools it can call to get or change things, and a loop that lets it call them repeatedly until the task is done.

The agent loop — why agents cost more than chatsEach step is a full model call that re-reads everything so far. Ten tool calls can bill 10× a single answer.Goalone instructionModel plansreads full historytool callTool runssearch, code, filesresultModel reads resultanother billed callrepeat until done — cap the number of steps and the token budget
Figure 1.The loop: read the current state (including the last tool result), decide the next action, act by calling a tool, and go round again until a stop condition is met.
The same request, handled two ways.
ChatbotAgent
You ask"Book me a table for four on Friday near the office""Book me a table for four on Friday near the office"
What happensIt writes a polite reply suggesting you check a booking siteIt searches nearby restaurants, checks Friday availability, picks one that fits, books it, and tells you the confirmation
Turns1As many as it takes: 4 to 8 here
What it neededNothingA search tool, a booking tool, a rule for when to stop
What it costOne short exchangeEvery turn re-sends everything so far (lesson 2)

One run, narrated

The booking agent, step by step

  1. 1

    Read

    The agent sees your request, its instructions, and the list of tools it is allowed to use. Nothing has happened yet.

  2. 2

    Decide

    It decides the first useful action is to search for restaurants near the office address. It writes that as a tool call, not as prose to you.

  3. 3

    Act

    The search tool runs and returns a list of eight places. That list is appended to the conversation.

  4. 4

    Read again

    Now the agent sees the request, the tools, its own search call, and the eight results. It decides to check Friday availability at the top three.

  5. 5

    Round and round

    Three availability checks, three results, one booking call, one confirmation. Each time, the whole history so far is what it reads.

  6. 6

    Stop

    It has a confirmation number, so it writes you a final message and the loop ends. Without a stop rule it could keep checking restaurants forever.

Knowledge check

What are the two things an agent has that a plain chatbot does not?

Lesson FAQ

What is an AI agent in plain English?

A chatbot that can take actions through tools and keeps going in a loop, reading the result of each action and deciding the next one, until the task is finished or a limit stops it. The model is the same as the chatbot; the loop and the tools are what is new.

Is ChatGPT an agent?

In its basic chat form, no: it answers once. Features that browse, run code, or complete multi-step tasks on your behalf are agent modes layered on top of the same model. The lesson's test is whether it acts and loops, not what it is called.

Do I need to code to use an agent?

Not to use one. Agent features exist inside the consumer apps, and lesson 3 shows how to get agent-style behaviour from an ordinary chat box. You need code only to build your own loop with your own tools.

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