How to brief an agent so it does what you want
Most bad results from AI agents aren't the agent's fault. They're briefings that were vague, missing context, or asking for three things at once. The good news: you don't need "prompt engineering" tricks. You need the same skill you'd use briefing a new assistant — saying clearly what you want, why, and what good looks like.
The four-part brief
Almost any task can be briefed well with four ingredients. You don't have to be formal about it; just make sure each one is covered.
1. The goal
Say what you want done in one sentence, as an action with a result. Not "tell me about camping stoves" — that's a topic, not a goal. Try: "Help me choose a camping stove for two people doing weekend car camping this summer." The agent now knows the job is choosing, not just describing.
2. The context
Everything the agent needs to know that you know and it doesn't. Budget, who it's for, what you've already decided, what you're trying to avoid. The camping-stove brief gets much better with: "Budget around $80, we cook simple meals, and I don't want anything complicated to clean." Without that, the agent guesses — and guesses are where bad results come from.
3. The constraints
What it must or mustn't do. "Don't recommend anything that needs special fuel." "Keep it under 300 words." "Only use the document I attached." Constraints are how you keep an agent from wandering off in an unhelpful direction. One common and powerful constraint: tell the agent what to do when it's unsure — "If you're not sure about something, say so instead of guessing."
4. The format
What you want back and in what shape. "A table comparing three options with price, weight, and one-line pros/cons." This matters more than people expect: an agent given no format defaults to a long essay, and a long essay is the worst shape for a decision. Tell it how you want to read the answer.
A before-and-after example
Before: "Write me an email to my landlord about the leak."
After: "Write a polite but firm email to my landlord (goal). The kitchen ceiling has been leaking for two weeks since I first reported it on the 10th, and there's now a water stain growing (context). Keep it under 150 words, reference the original report date, and don't threaten legal action (constraints). Give me the email text only, with a clear subject line (format)."
The second version takes thirty seconds longer to write and gets you a usable email on the first try instead of the third. That's the whole game.
Five habits that improve everything
- Give examples. "Like this, but shorter" with a pasted example works better than any description of tone. Show, don't describe.
- One job per request. "Research kayaks, then write me a workout plan" gets you two mediocre halves. Split big asks into separate requests, in order, and use the output of one as the input to the next.
- Name your audience. "Explain it like I'm new to this" vs. "Give me the technical version" produces completely different answers. Always say who the answer is for.
- Invite questions. "Ask me anything you need before you start" is a great line. A good agent will surface the missing context instead of silently guessing — and you'll often learn your brief had a hole.
- Iterate, don't restart. If the result is 80% right, say what's wrong and ask for a revision: "Good, but make the tone friendlier and cut the second paragraph." Refining beats starting over almost every time.
The mistake to avoid
The most common mistake is the mind-reading brief: giving the agent a vague request and getting annoyed when it doesn't read your mind. "Make me a schedule" tells the agent nothing about your hours, your commitments, or what "good" means. Every vague brief costs you a round-trip of corrections. Spend the minute up front — it's the highest-return minute in the whole process.
Next: checking an agent's work before you rely on it — because even a well-briefed agent needs a second pair of eyes.