Prompt Engineer

Prompt Engineering

Design and optimize prompts for production LLM applications with structured outputs, caching, and evaluation.

Arguments: $ARGUMENTS - goal description, existing prompt to refine, or audit to review prompts in the current codebase

Behavior

1. Detect Mode

# Check if auditing existing prompts or designing new ones
if [[ "$ARGUMENTS" == "audit" ]]; then
  grep -rn "system_prompt\|SYSTEM\|<system>\|role.*system\|systemPrompt" . \
    --include="*.py" --include="*.ts" --include="*.js" --include="*.md" \
    -l 2>/dev/null | head -20
fi

2. For New Prompt Design

Gather context first:

# Check if project uses Anthropic SDK
grep -r "anthropic\|claude" package.json requirements.txt pyproject.toml 2>/dev/null | head -5
# Check for existing prompt patterns
find . -name "*.md" -path "*/prompts/*" -o -name "*prompt*" -not -path "*/node_modules/*" 2>/dev/null | head -10

Apply these patterns based on the goal:

System prompt structure:

<system>
You are [role]. Your task is [specific task].

Rules:
- [constraint 1]
- [constraint 2]

Output format: [JSON schema / markdown / plain text]
</system>

Few-shot examples (include 2-3 for classification/extraction tasks):

<examples>
<example>
<input>...</input>
<output>...</output>
</example>
</examples>

Chain-of-thought (use for reasoning tasks):

Think through this step by step before answering.
First, identify... Then, determine... Finally, output...

Structured output (prefer when consuming programmatically):

# Use with tool_use or response_format for guaranteed JSON

3. Caching Strategy

Identify cacheable vs. dynamic parts:

• Cache: system prompt, few-shot examples, static context (documents, schemas)
• Dynamic: user message, session history, runtime variables

# Anthropic prompt caching pattern
messages = [
    {
        "role": "user",
        "content": [
            {
                "type": "text",
                "text": static_context,
                "cache_control": {"type": "ephemeral"}  # cache this block
            },
            {
                "type": "text",
                "text": user_query  # not cached — changes each turn
            }
        ]
    }
]

Cache breakeven: ~1,000 tokens. Cache everything above that threshold that doesn't change per-request.

4. For Prompt Audits

Review each found prompt for:

• Ambiguity: instructions that could be interpreted multiple ways
• Missing constraints: what the model should NOT do
• Output format: is it specified? is it enforced?
• Caching opportunity: is static context sent uncached every call?
• Token waste: repeated instructions that could be in system prompt

Report format:

File: src/prompts/classifier.py
Issues:
  [HIGH] No output format specified — add JSON schema or example
  [MED]  Static 2KB context sent uncached — add cache_control
  [LOW]  Instruction "be helpful" is redundant — remove

5. Evaluation Checklist

Before finalizing a prompt:

• Tested with at least 5 diverse inputs
• Edge cases handled (empty input, adversarial input, off-topic)
• Output format enforced (not just requested)
• Caching applied to static blocks > 1,000 tokens
• System prompt under 500 tokens where possible (use cache for longer)
• No hallucination-prone instructions ("always answer confidently")

Examples

/prompt-engineer "classify customer support tickets into 5 categories and return JSON"
/prompt-engineer "refine this system prompt: <paste prompt>"
/prompt-engineer audit

Token Optimization

Expected range: 400–1,200 tokens (new design), 600–2,000 tokens (audit)

Early exit: Audit with no LLM prompt files found → reports "no prompts detected" immediately.

Grep-before-Read: Locates prompt files via grep before reading any content.

Patterns used: Grep-before-Read, early exit, progressive disclosure (issues by severity)