2.2 — System Prompts, Templates, and Guardrails

CCAR-P Domain 2 · Task 2.2

What You Need to Know

System prompt = standing contract (role, audience, policy, output format). User turns carry per-request data. Template = prompt with named slots. Guardrail = limit on what the model receives or returns.

System Prompt as Architectural Contract

Stable authority; cacheable prefix. Altitude rule: specific enough to guide, flexible enough for heuristics. Avoid both brittle hardcoded logic and vague high-level guidance.

Explicit Instructions + Escape Hatch

State role, audience, rules, conflict resolution, output format. Give motivation where helpful. Escape hatch = what to do when the task cannot be done honestly (null, “not enough information”). Without one, the contract forces invention.

Templates as Engineering Artefacts

Named slots → testable, versionable, reviewable. Use consistent XML tags for content types. Prompts in production are code.

Guardrails in Layers

1. Instruction-level — scope, refusal rules, tone, escape hatch
2. Input-side — validate/sanitise; delimit untrusted content as data (not instructions)
3. Output-side — schema + business-rule validation before downstream consumption

Every refusal needs a route (human queue, structured error). Instructions shape behaviour probabilistically; only programmatic validation guarantees it.

Exam Traps

• Restating standing policy in every user turn instead of system prompt
• Responding to invented-fact incidents with larger model / lower temperature
• Relying on system-prompt instructions as sole guardrail
• Keeping every schema field mandatory + “never invent” rule