Context, Objective, Actions, Scenario, Task — A five-part framework for detailed, multi-constraint tasks.
COAST is worth the extra structure when a task has several moving parts that all need to be specified — detailed business writing, planning documents, or anything where leaving out one piece of context would meaningfully change the output.
The background situation the task exists within.
What you're trying to achieve overall.
The specific things the AI needs to do to get there.
The concrete situation or constraints the actions need to account for.
The precise deliverable you want at the end.
Bad prompt:
“Write a business plan for my idea.”
Structured with COAST:
Context: I'm starting a subscription coffee roasting business, solo founder, no funding yet. Objective: I need a plan that helps me decide if this is worth pursuing before I invest more time. Actions: Estimate startup costs, identify the biggest risk, and outline a lean first 90 days. Scenario: I can work on this part-time for now and have about $5,000 to start. Task: A one-page lean plan, not a full formal business plan document.
A one-page lean plan covering rough startup costs within the stated budget, the single biggest risk to the idea, and a 90-day outline sized for part-time effort — not a formal multi-section business plan.
COAST is a good fit for both ChatGPT and Claude on detailed planning tasks, and its explicit Scenario section helps keep longer Claude outputs grounded in real constraints instead of generic advice.