Prompt Design for Agents

A system prompt is the operating manual for an agent. It determines output quality more than model selection, tool design, or orchestration architecture. A well-prompted Sonnet outperforms a poorly-prompted Opus. Invest more time here than anywhere else in agent design.

The principle: write the prompt as if you're onboarding a smart new hire who has zero context on your company, your process, or your quality bar. Be explicit about what good looks like. Show, don't just tell.

Prompt Architecture

Every agent system prompt follows the same 7-section structure. Order matters. The model pays more attention to content earlier in the prompt.

1. Identity        — Who the agent is and what it does (2-3 sentences)
2. Input spec      — What the agent receives and in what format
3. Output spec     — Exact format, schema, required fields
4. Process         — Step-by-step instructions for how to get from input to output
5. Rules           — Hard constraints the agent must never violate
6. Examples        — 2-3 input/output pairs showing ideal behavior
7. Edge cases      — What to do when data is missing, ambiguous, or unexpected