| name | prompt-engineering |
| description | Rules and frameworks for writing high-quality LLM system prompts. Use this skill whenever you are authoring, reviewing, editing, or optimizing a system prompt — including when generating a system prompt as part of building an agent, tool, or workflow. Trigger on any task that involves writing instructions for an LLM, crafting a system message, tuning prompt wording, or reviewing an existing prompt for quality. Even if the user doesn't say 'system prompt' explicitly, use this skill when the output will be consumed as LLM instructions. |
Prompt Engineering
Reference for writing and reviewing LLM system prompts.
Based on Harada et al. (2024) — Curse of Instructions, EARS syntax, and ARQ pattern.
1. Minimize the Rule Count (Curse of Instructions)
The probability of the model following all rules simultaneously is approximately P = p^N, where N is the number of independently verifiable instructions and p is the per-rule adherence rate.
| N rules | p = 0.95 | p = 0.90 |
|---|
| 5 | 77% | 59% |
| 10 | 60% | 35% |
| 20 | 36% | 12% |
| 30 | 21% | 4% |
Target: 10 or fewer distinct rules in the system prompt.
The math is unforgiving — every additional rule multiplicatively reduces the chance the model follows all of them. This is why minimizing rule count matters more than perfecting any single rule.
- Move procedural/structural rules (e.g., parameter formatting, count constraints) into tool descriptions, not the system prompt.
- Merge rules that protect the same invariant into one EARS statement.
- Delete rules already enforced by the tool schema or the agent framework.
2. Write Rules in EARS Syntax
Easy Approach to Requirements Syntax produces unambiguous, testable rules. Free-form instructions invite misinterpretation because the model has to guess the scope and trigger condition. EARS removes that ambiguity.
Four forms:
| Form | Template | Use when |
|---|
| Ubiquitous | The system shall [action]. | Rule always applies |
| Event-driven | When [trigger], the system shall [action]. | Rule fires on a condition |
| State-driven | While [condition], the system shall [action]. | Rule applies during a state |
| Unwanted behavior | If [situation], the system shall [response]. | Error / boundary case |
Before (free-form): "NEVER output a URL that contains {product_name} as a literal string. Always make sure the product name is properly substituted before including any link."
After (EARS): "If a URL contains an unresolved template placeholder, the system shall omit the link and respond without it."
The EARS version is shorter, has one clear trigger, and one clear action — no room for partial compliance.
3. Five Failure Patterns to Detect
When reviewing a prompt, check for structural signals of each pattern. These patterns emerge from how prompts grow organically over time — patches on patches — and each one has a telltale signature in the prompt text.
| Pattern | What happens | Signal in the prompt |
|---|
| Focus loss | Model satisfies some constraints but silently drops others | Post-response self-check blocks; mandatory verification sections |
| Context misinterpretation | Query routed to wrong product or tool | Same routing rule restated in 3+ sections with slightly different wording |
| Hallucination | Model invents values for parameters it cannot resolve | Same constraint (e.g., "never output unresolved URLs") in both system prompt AND tool descriptions |
| Business protocol bypass | Access control, upsell, or boundary responses skipped | Multiple alternative response templates for the same situation (Option A / B / C) |
| Instruction ignored | Specific operational rules (count, format, single call) repeatedly violated | Rule exists only because the model kept breaking it — belongs in tool description, not system prompt |
4. ARQ Reasoning Scaffold (VERIFY Step)
Attentive Reasoning Query pattern: include a numbered VERIFY checklist as the last step of the workflow. Each item maps 1:1 to one EARS rule, forcing instruction-level chain-of-thought before output.
VERIFY before responding:
1. [EARS rule 1 — single sentence]
2. [EARS rule 2 — single sentence]
3. [EARS rule 3 — single sentence]
...
This makes multi-instruction compliance explicit and testable. Per Harada et al. (2024), instruction-level chain-of-thought improves all-rules compliance by 2-3x on GPT-4o and Claude 3.5 Sonnet.
Keep the VERIFY list to 8 items or fewer. If you need more, consolidate rules first — a long VERIFY list defeats the purpose.
5. Structural Rules
- One truth per rule. If the same invariant is stated in two places, pick the most authoritative location and delete the duplicate. Duplication is how hallucination patterns start (Section 3).
- Urgency markers devalue each other. Use CRITICAL/MANDATORY for at most 2 rules per prompt. If everything is critical, nothing is.
- Static before dynamic. Put the unchanging role/rules at the top. Inject dynamic context (product lists, user data) at the bottom. This enables prompt caching and keeps the model's attention on rules first.
- Examples cost tokens. Include examples only for non-obvious rules. One positive + one negative example per rule is enough.
- Patch-on-patch is a signal. If you find rule -> exception -> exception-to-exception chains, consolidate. Organic growth via successive fixes is the most common source of rule-count bloat.
