You'll leave with: a one-page Agent Brief you can paste into any AI tool. Writing it first saves hours of rebuilding.
Why a brief first?
Most “bad agents” are bad briefs: a vague goal, no limits, and no way to tell when it's wrong. A page of planning fixes most of that. It uses the same ideas from Lesson 2 (role, context, task, format, constraints) but adds three things an agent needs: tools, limits, and a truth test.
The six boxes of an Agent Brief
| Box | Question | Example (Dinner Planner) |
|---|---|---|
| 1. Goal | What does “done” look like? | A dinner for 4, a grocery list, and a total I can verify, under $40. |
| 2. Instructions | What steps and style should it follow? | Ask 4 questions first. Build a table. Re-add the total twice. |
| 3. Tools | What can it do besides write? | None needed to start (copy and paste). Optional: web search for prices. |
| 4. Context | What does it need to know each time? | People, budget, diet, time available, my usual store. |
| 5. Limits | What must it never do, or ask first? | Never buy, never log in to a store, label every estimate. |
| 6. Truth test | How will I know the output is right? | I add the column myself and spot-check two prices. |
Tools: start with none
Each tool you add (web search, files, email, spreadsheets) is a new way for the agent to be helpful, and a new way for it to go wrong. Start with no tools: you copy and paste. Add one tool at a time, only when the copy-paste version works reliably. The principle is “least access”: the agent gets only what it needs for the job.
Limits: write the “nevers”
Good limits are specific: “Never send an email. Only draft.” “Never enter payment details.” “Ask me before doing anything that costs money or can't be undone.” Put them in the instructions and keep them in your own habits: don't connect accounts you wouldn't hand to an intern.
Truth test: how you'll catch mistakes
Choose the check before the first run. Sums: add them yourself. Dates: check the calendar. Quotes: open the source. If you can't think of a way to check the result, the agent is not ready for that job.
The Agent Brief template
AGENT BRIEF: [NAME] 1. GOAL: [what "done" looks like, in one sentence] 2. INSTRUCTIONS: - Step 1: [ask me for ...] - Step 2: [do ...] - Step 3: [check ... and report ...] 3. TOOLS: [none / web search / files / ...]. Use only these. 4. CONTEXT I will provide each time: [list] 5. LIMITS: Never [X]. Ask before [Y]. Label anything you are unsure about as "estimate". 6. TRUTH TEST (what the user will check): [e.g. totals, dates, sources] 7. OUTPUT FORMAT: [table / bullets / email draft], under [N] words.
Exercise
Fill in the Agent Brief for one job you'd like an intern to do. Choose something low-stakes, like a weekly meal plan, a reading summary, or a packing list.
- Write the goal and make sure “done” can be checked.
- List the tools. Delete all but the minimum.
- Write three “nevers”.
- Write the truth test. If you can't, pick a different job.
Compare yours with the ten ready-made packs in the Agent Library. Notice how each has role, steps, rules and an output format.
Key takeaways
- An agent brief has six boxes: goal, instructions, tools, context, limits, truth test.
- Start with no tools. Add one at a time.
- Pick your truth test before the first run.
Related: Open the Agent Library
Sources
Checked November 10, 2026 (Eastern Time). Plans, limits and features change: confirm on the official page.