I found a prompt that keeps AI agents from taking tasks too far

But it can still be hard to predict what an AI might do in the heat of the moment, particularly when it comes to how—and when—they’ll decide they’re actually finished with the task you’ve handed them.

Here’s where a key facet of AI prompting comes into play. One handy way to keep ChatGPT, Claude, or Gemini from taking a potentially destructive command too far is to carefully describe your desired outcome.

Or put another way, you can make the AI define what “done” means for a given task. This whole “define done” concept isn’t new. It’s a popular prompting concept that helps the AI to stay on course and avoid giving you a rude surprise at the end.

Many different versions of the “define done” prompt exist. I took the bones of one such prompt and honed it with the help of GPT 5.6 Sol (the model that powers ChatGPT Work) and Claude Opus 5, going back and forth until the prompt was working the way I expected.

Here’s the prompt:

Before you start, give this task a clear finish line. Keep it brief and proportional to the size of the job.

**Result:** What will be true when the task is finished.

**What you’ll produce:** The specific thing you’ll make or change.

**How I’ll know:** Something I can inspect, test, count, or otherwise verify for myself.

**Not part of done:** Related work you might notice but will leave alone.

**Open questions:** Anything ambiguous that would change what “done” means. If there are none, write “none.”

Use the smallest complete version of my request. Avoid vague goals like “improve” or “optimize.”

Then stop. Do not begin work in the same reply — wait for my go-ahead. Once I approve, stop as soon as the check passes. If you notice anything else, list it separately under “Not part of this task,” but don’t act on it unless I ask.

And here’s a more compact and portable version: