Build your first AI agent

An agent with no stop rules loops for an hour or quietly invents the one number it could not find.

How-to

Here are the three routes open today, and a brief with the stop conditions already written in.

What makes it an agent

Anthropic's engineering post draws the line, and the company still links it from its agents page. A workflow is a system where the model and its tools run through "predefined code paths" you decided in advance. An agent is a system where models "dynamically direct their own processes and tool usage, maintaining control over how they accomplish tasks".

So the test is one question: can you write the exact steps out before it starts? If you can, build an automation, which will be cheaper and more reliable. If the next move depends on what it finds, you want an agent.

The same post says agentic systems "trade latency and cost for better task performance", so add one "only when simpler solutions fall short".

Three doors that are open today

Every route below was checked on 16 September 2026, because this is a field where last year's tutorial sends you somewhere that no longer exists.

Claude Cowork, if you already pay for Claude

What it is: the closest thing to a full agent loop without writing anything. You give it a goal, it works across your files and tools, and you come back to finished work.

The cost: it runs on Pro, Max, Team and Enterprise, and Pro is $17 a month billed annually or $20 monthly. The free plan does not include it.

The gentlest start: the approval setting, which is manual approval, auto with a safety review, or skip all approvals. Leave it on manual for the first month.

ChatGPT Work, if ChatGPT is the one you already have open

What it is: where OpenAI's agent work lives now. In the desktop composer you choose between Cloud and Work locally, and the local option needs the desktop app running. Recurring runs are scheduled tasks.

One dated thing to know before you build on it: OpenAI says GPT-5.5 retires from ChatGPT, ChatGPT Work and Codex on 14 October 2026, and tells people to replace it in any scheduled task that uses it.

A no-code builder, if the job crosses apps you do not want to connect by hand

The options: Zapier Agents reaches across its app library with no code and has a free tier at 400 activities a month. n8n is free if you self-host and €20 a month on annual billing for the cloud starter.

The trade: both are better than Claude or ChatGPT at the plumbing between services, and worse at judgement.

Prices are in each vendor's own currency. Claude skills are a free route too: they work on the free plan and are the cheapest way to change how an agent behaves without building one at all.

What died recently, so you do not start there

The answer changed twice this quarter, which is why r/AI_Agents keeps asking which platform to trust.

  • Relay.app shut down. Free users on 15 August 2026 and paying customers on 14 September.
  • ChatGPT agent is no longer available. OpenAI's help page now sends you to ChatGPT Work instead, so any guide naming Agent mode is stale, and OpenAI's own Agent Builder was deprecated in June 2026 and shuts down on 30 November.
  • Gumloop costs from the start. It begins at $37 a month plus an 8% orchestration fee, and its trial needs a card.
  • Lindy has no free plan. It starts at $29.99 per user a month, and its credits do not roll over.

That churn is the argument for the approach here: build the smallest loop that works, on a surface you already pay for, before you go shopping for a platform.

1. Pick the job before you pick the tool

The advice that keeps coming back on r/AI_Agents from people who have shipped one: map what you do, find the most repetitive thing, build for that one. The prompt below does that interrogation properly, because the job you first think of is usually either too big or better built as an automation.

PromptPick my first agent
You are helping me choose the first AI agent I build. Most first agents fail because the job was wrong, so your job is to talk me out of the bad ones before I waste a week. Be blunt. If nothing I describe is a good first agent, say so and tell me to keep using chat.

ASK ME THESE FIRST, IN ONE MESSAGE, AND WAIT FOR THE ANSWERS

1. What are the three most repetitive things you did at work or at home in the last fortnight? Describe each one as what you actually did, step by step, not as a job title.
2. For each one, how often does it happen, and roughly how long does it take?
3. Which AI tools do you already pay for, and which do you already have open every day?
4. What can the AI reach on your machine or accounts right now: files, email, calendar, a spreadsheet, a project tool, nothing yet?
5. What is the worst thing that happens if it gets one of these wrong and nobody notices for a day?

DO NOT RECOMMEND ANYTHING UNTIL YOU HAVE ALL FIVE. If I skip one, ask again for that one.

THEN SCORE EACH CANDIDATE AGAINST THESE FIVE, OUT OF 5

- REPEATS: does it happen at least weekly? A job done twice a year is not worth automating.
- JUDGEMENT: does the next step depend on what it finds? If I could write every step out in advance, tell me plainly that this is an automation, not an agent, and that an automation will be cheaper and more reliable.
- REACHABLE: can the tools I already have actually touch the things this job needs? If not, say which piece is missing.
- CHECKABLE: could I tell within two minutes whether the output is right? If the answer is no, this is a bad first agent, because I will not catch its mistakes.
- SAFE TO GET WRONG: does a mistake cost me an hour or cost me a client? Anything that sends, pays, deletes, or is seen by someone else scores low here and needs an approval step.

THEN GIVE ME

- The one job you recommend, with its scores and one sentence on why it beat the others.
- The two you are rejecting, and the specific reason each one fails. Do not be diplomatic about this.
- Which of my existing tools I should build it on, based on what I said in questions 3 and 4, not on what is most capable in general.
- The smallest possible first version: the version that does one pass, on one input, and shows me the result without acting on it.
- What has to be true before I let it run unattended.

NEVER
- Never recommend a tool I did not say I have unless you explicitly flag that it means a new subscription and tell me the cost is unverified and I should check it myself.
- Never tell me a job is a good fit to be encouraging. A wrong yes here costs me the week.
- Never invent a capability. If you are not sure whether a tool can reach my files or my inbox, say you are not sure and tell me how to check in one step.

FINISH WITH
One paragraph I can reuse as the brief for this agent, written as a goal rather than a set of instructions, plus the single thing most likely to make it fail.

2. Write the brief, with the stop conditions in it

The stop conditions belong in the brief, because a first agent fails by not stopping. Tiffany Teasley, a data scientist who writes about building these, put the loop in four words in June 2026, "think, act, observe, repeat".

She also names the bit the vendor pages leave out: they "loop when they should stop", they "call the wrong tool", and the tutorials only ever show the happy path.

PromptThe agent brief
This is a standing brief for a job I want you to do end to end. Work towards the goal rather than following my steps literally, because I cannot know in advance what you will find. Everything below that says STOP or ASK is a hard rule, and I would rather you come back with half the job and a clear question than a finished-looking answer with a guess inside it.

THE GOAL
[One sentence. What I want to be true when you are done. Not how to do it.]

WHEN THIS RUNS
[On demand / every Monday morning / whenever I say the trigger phrase, which is: run the weekly readout]

WHAT YOU CAN REACH
- Files or folders: [name them exactly, or "none"]
- Accounts and tools: [name them, or "none"]
- The web: [yes / no / only these sites, listed here: ]
If any of those is wrong or you cannot reach something listed, STOP and tell me before you start, rather than working around it.

WHAT DONE LOOKS LIKE
[The actual artefact. A file at a named path, a draft in a named place, a summary in the chat. Say the format and where it goes.]

HOW TO WORK
1. Before acting, tell me your plan in no more than five lines: what you will look at, in what order, and what you will produce. For the first three runs, stop there and wait for me to say go. After that, start straight away unless something in the plan touches the STOP list below.
2. Work in passes. After each pass, note in one line what you found and what you are doing next.
3. If two sources disagree, use neither. Record both, flag the conflict, and carry on with the rest.

STOP AND ASK ME FIRST, ALWAYS, BEFORE
- Sending anything to another person: an email, a message, a calendar invite, a comment.
- Spending money or entering payment details.
- Deleting or overwriting anything that is not a file you created in this run.
- Posting anywhere public.
- Doing anything that was not in the goal above, however sensible it seems.

STOP AND COME BACK TO ME IF
- You have done three passes without getting closer. Do not keep trying. Report where you got stuck and what you tried. (Raise or lower that number here if three is wrong for this job.)
- A step fails twice for the same reason.
- The job turns out to be bigger than the goal describes.
- You find something that changes whether this job is worth doing at all.

NEVER INVENT
- If a number, a name, a date or a source is missing, write "[NOT FOUND]" and say exactly where you looked. Never estimate one to complete the shape of the output.
- Never fill a gap from general knowledge and present it as something you retrieved. If you know something from training rather than from my files, label it.
- Never claim you did something you could not verify. "I updated the tracker" must mean you can point at the change.

FINISH EVERY RUN WITH
- What you produced, and where it is.
- What you could not do, and why. If everything worked, say so in one line.
- Every "[NOT FOUND]" in one list, so I can fill them.
- Anything you noticed that I did not ask about but should know.
- One line on what would make the next run better.

Where the brief goes

  • Claude Cowork. The instructions on a new task.
  • ChatGPT Work. Paste it as the task itself, or save it as a scheduled task.
  • Zapier Agents. The agent's behaviour or instructions field.
  • n8n. The system prompt on the agent node.

Wherever it lands, keep the goal at the top and the STOP list intact, because that is the part every interface tempts you to trim.

The honest bit

Agents cost more than chat, and the meters count in units you would not expect. Anthropic says plainly that Cowork "consumes more of your usage allocation than chatting with Claude", and that allocation is shared across Claude Code, chat and Cowork on a rolling five-hour window with weekly caps on top.

Zapier counts an activity every time an agent uses a tool, searches the web or queries a knowledge source, so 400 free activities a month is nothing like 400 tasks. n8n counts a whole workflow run as one execution however complicated it is, and Gumloop adds 8% on top as an orchestration fee.

A language model also does not do the same thing every time the way an ordinary program does, so the same brief on the same inputs can give you a different answer on Tuesday. Anthropic's help pages say it plainly: no defence is perfect and no permission mode replaces your judgement.

Build the smallest one this week

Run the picker, take the job it chooses, and give it the brief with the stop conditions filled in. Keep approvals on manual, let it do one pass on one real input, and read what it says it could not do, because that list is where you learn what your setup is missing.

If you want the shape of the loop in someone else's words first, Tiffany Teasley's afternoon walkthrough from June 2026 is the clearest beginner account I have found, failures included.

And for the cheapest possible taste of changing how an agent behaves, a one-file skill called i-have-adhd, MIT licensed and over 46,000 stars as of 16 September 2026, does nothing but stop a coding agent burying the answer under its own explanation. It adds no capability at all, which is rather the point.

A few quick questions

Do I need to code?

No, for all three routes above. Claude Cowork and ChatGPT Work take a written brief, and Zapier Agents and n8n are visual. Coding buys you control you will not need for a first agent.

What is the cheapest way to try this?

Three free doors: Zapier Agents gives 400 activities a month free, n8n is free if you self-host it, and Claude skills work on the free plan. Claude Cowork needs a paid plan, from $17 a month billed annually.