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Prompt Engineering
Prompt engineering is the practice of designing inputs to language models to reliably
elicit high-quality, accurate, and appropriately formatted outputs. It covers everything
from writing system instructions to multi-step reasoning pipelines and retrieval-augmented
generation. Effective prompting reduces hallucinations, improves consistency, and unlocks
capabilities the model already has but needs guidance to apply. The techniques here apply
across providers (OpenAI, Anthropic, Google) with minor syntactic differences.
When to use this skill
Trigger this skill when the task involves:
Writing or refining a system prompt for an agent or chatbot
Implementing chain-of-thought reasoning to improve accuracy on hard tasks
Designing few-shot examples to steer model behavior
Building a RAG pipeline (retrieval + context injection + generation)
Getting structured JSON/schema output from a model reliably
Evaluating or benchmarking prompt quality across dimensions
Choosing between zero-shot, few-shot, fine-tuning, or RAG approaches
Debugging inconsistent or hallucinated model outputs
Do NOT trigger this skill for:
Model training, fine-tuning infrastructure, or RLHF pipelines (those are ML engineering)
Framework-specific agent wiring (use the mastra or relevant framework skill instead)
Key principles
Be specific and explicit - Vague instructions produce vague outputs. State the
audience, format, length, tone, and constraints in every prompt.
Provide context before instruction - Background and examples before the task
reduces ambiguity. The model reads top-to-bottom; front-load what matters.
Use structured output - Request JSON, markdown tables, or a fixed schema when
downstream code will consume the response. Pair with schema validation and retries.
Iterate and evaluate - Treat prompts as code. Version them, test against a
golden eval set, and measure regressions before deploying changes.
Decompose complex tasks - A single prompt asking the model to research, reason,
and format simultaneously degrades quality. Break into sequential or parallel calls.
Core concepts
System / user / assistant roles
Role
Purpose
Notes
system
Persistent instructions, persona, constraints
Set once; applies to full conversation
user
The human turn - questions, tasks, data
Can include injected context (RAG, tool output)
assistant
Model response (or prefill to steer format)
Prefilling forces a specific start token
Temperature and sampling
temperature: 0 - Deterministic, best for factual extraction and structured output
temperature: 0.3-0.7 - Balanced creativity and coherence; good for most tasks
temperature: 1.0+ - High diversity; useful for brainstorming, risky for factual tasks
top_p (nucleus sampling) - Alternative to temperature; values 0.9-0.95 are common
Never set both temperature and top_p to non-default at the same time
Token economics
Input tokens cost less than output tokens on most providers - keep outputs focused
Longer context = slower TTFT (time to first token) and higher cost
Modern models: 128K-1M token windows, but quality degrades near limits ("lost in the middle")
Place critical instructions at the start and end of long prompts
For RAG: inject only top-K retrieved chunks, not entire documents
Summarize long conversation history rather than passing raw transcripts
Prompt vs fine-tuning decision
Scenario
Approach
New behavior, few examples
Zero-shot or few-shot prompting
Consistent style/format needed
Few-shot or system prompt
Thousands of labeled examples + consistent task
Fine-tuning
Domain knowledge too large for context
RAG
Latency-critical, repeated same task
Fine-tune for smaller/faster model
Common tasks
Write effective system prompts
Template:
You are [PERSONA] helping [AUDIENCE] with [DOMAIN].
Your responsibilities:
- [CORE TASK 1]
- [CORE TASK 2]
Constraints:
- [HARD RULE 1 - what to never do]
- [HARD RULE 2]
Output format: [FORMAT DESCRIPTION]
Concrete example:
You are a senior code reviewer helping software engineers improve TypeScript code quality.
Your responsibilities:
- Identify bugs, logic errors, and type safety issues
- Suggest idiomatic improvements with brief reasoning
- Flag security vulnerabilities explicitly
Constraints:
- Never rewrite the entire file unprompted; focus on the diff
- Do not praise code unless it exemplifies a non-obvious pattern worth reinforcing
Output format: Return a markdown list of findings. Each item: [SEVERITY] - description.
Anti-patterns:
"Be helpful, harmless, and honest" (too generic - the model already knows this)
Contradictory constraints ("be concise" and "explain everything in detail")
No output format specification when downstream parsing is required
Implement chain-of-thought
Zero-shot CoT - append "Let's think step by step." to trigger reasoning:
User: A store has 3 boxes of apples, each containing 12 apples. They sell 15 apples.
How many remain? Let's think step by step.
Structured CoT - define explicit reasoning steps:
System: When solving math or logic problems, follow this structure:
1. UNDERSTAND: Restate what is being asked
2. PLAN: List the operations needed
3. EXECUTE: Work through each step
4. ANSWER: State the final answer clearly
User: [problem]
Self-consistency (sample multiple reasoning paths, majority-vote the answer):
Use CoT for arithmetic, logic, multi-step planning, and ambiguous classification.
Skip CoT for simple lookup tasks - it adds tokens without benefit.
Design few-shot examples
Selection criteria:
Cover the most common input patterns (not edge cases for initial shot selection)
Include at least one negative/refusal example if the model should decline certain inputs
Keep formatting identical across all examples - models learn from structural patterns
Ordering:
Most representative examples first; most recent (closest to the query) last
For classification: interleave classes rather than grouping them
Formatting template:
System: Classify the sentiment of customer reviews as POSITIVE, NEGATIVE, or NEUTRAL.
User: Review: "The product arrived on time but the packaging was damaged."
Assistant: NEGATIVE
User: Review: "Exactly as described, fast shipping. Very happy!"
Assistant: POSITIVE
User: Review: "It works."
Assistant: NEUTRAL
User: Review: "{actual_review}"
3-8 examples typically saturate few-shot gains. More examples rarely help and
consume context budget that could be used for the actual input.
Build a RAG prompt pipeline
Step 1 - Retrieval: embed the query and fetch top-K chunks from a vector store.
Step 2 - Context injection:
System: You are a documentation assistant. Answer questions using ONLY the provided
context. If the answer is not in the context, say "I don't have that information."
Context:
---
{retrieved_chunk_1}
---
{retrieved_chunk_2}
---
User: {user_question}
Step 3 - Generation with citation:
System: [...as above...]
After your answer, list sources as: Sources: [chunk title or ID]
User: How do I configure authentication?
Key decisions:
Chunk size: 256-512 tokens for precision; 1024 for broader context
Overlap: 10-20% of chunk size to avoid cutting mid-sentence
Reranking: use a cross-encoder reranker after initial retrieval to improve top-K quality
Query rewriting: expand ambiguous queries before embedding for better recall
Never inject raw retrieved text without a clear delimiter. Models need structural
separation to distinguish context from instructions.
Get structured JSON output
Schema enforcement via function calling / structured output (preferred):
defextract_json(prompt: str, schema: dict, max_retries=3) -> dict:
for attempt inrange(max_retries):
raw = llm.complete(f"{prompt}\n\nRespond with valid JSON matching: {schema}")
try:
data = json.loads(raw)
validate(data, schema) # jsonschemareturn data
except (json.JSONDecodeError, ValidationError) as e:
prompt += f"\n\nPrevious response was invalid: {e}. Fix and retry."raise RuntimeError("Failed to get valid JSON after retries")
Always validate parsed JSON against a schema - do not trust model-generated structure
blindly. Use response_format: json_object as a minimum guardrail.
Implement prompt chaining
Decomposition pattern - split a complex task into sequential LLM calls:
# Step 1: Research
research = llm.complete(f"List key facts about: {topic}")
# Step 2: Outline
outline = llm.complete(f"Given these facts:\n{research}\n\nCreate a structured outline.")
# Step 3: Write
article = llm.complete(f"Outline:\n{outline}\n\nWrite the full article.")
Routing pattern - use a classifier call to select the right downstream prompt:
intent = llm.complete(
f"Classify this request as one of [refund, technical, billing, other]: {user_message}"
)
handler_prompt = PROMPTS[intent.strip().lower()]
response = llm.complete(handler_prompt.format(message=user_message))
Verification pattern - add a critic call after generation:
draft = llm.complete(task_prompt)
critique = llm.complete(
f"Review this output for accuracy and completeness:\n{draft}\n\n""List any errors or missing information. If none, respond 'APPROVED'."
)
if"APPROVED"notin critique:
final = llm.complete(f"Revise based on this critique:\n{critique}\n\nDraft:\n{draft}")
Evaluate prompt quality
Metric
How to measure
Target
Accuracy
Compare to golden answers on eval set
Task-dependent; establish baseline
Consistency
Run same prompt N times, measure output variance
< 10% divergence for deterministic tasks
Format compliance
Parse output programmatically; count failures
> 99% for production structured output
Latency
P50/P95 TTFT and total response time
Set SLA before optimizing
Cost
Input + output tokens x price per token
Track per-request; alert on spikes
Hallucination rate
Human eval or reference-based metrics (RAGAS for RAG)
Establish red lines
Eval harness pattern:
results = []
forcasein eval_set:
output = llm.complete(prompt.format(**case["inputs"]))
results.append({
"id": case["id"],
"pass": case["expected"] in output,
"output": output,
})
print(f"Pass rate: {sum(r['pass'] for r in results) / len(results):.1%}")
Anti-patterns / common mistakes
Anti-pattern
Problem
Fix
Asking multiple unrelated questions in one prompt
Model answers one well, ignores others
One task per prompt; chain calls
System prompt with no output format
Responses vary wildly across runs
Always specify format, length, structure
Using temperature > 0 for structured extraction
JSON parse failures increase dramatically
Set temperature: 0 for deterministic tasks
Injecting entire documents into context
"Lost in the middle" - model ignores center of context
Chunk and retrieve only relevant passages
No eval set before shipping a prompt
No way to detect regressions
Build a 20+ case eval set before production
Trusting model output without validation
Downstream failures, security issues
Parse + validate + retry on failure
Gotchas
Temperature > 0 for structured extraction - Even temperature: 0.1 meaningfully increases JSON parse failure rates. Always use temperature: 0 when the output must be parsed programmatically. This is the single highest-yield change for reliability.
RAG context injected without delimiters - When retrieved chunks are concatenated directly into the prompt without separators (--- or XML-style tags), models confuse retrieved content with instructions. Always use explicit structural delimiters around each retrieved chunk.
Verification pattern creates hallucination loops - The critic-and-revise pattern can cause a model to confidently generate new hallucinations to "fix" non-existent errors. If the draft is factually grounded, set a high bar for what triggers revision - don't revise unless there's a concrete, checkable error.
Few-shot examples grouped by class - In classification prompts, showing all POSITIVE examples first then all NEGATIVE examples trains the model to pattern-match on recency rather than semantic content. Interleave classes in few-shot examples.
System prompt changes not tracked against an eval set - Prompt changes that feel like improvements often degrade performance on edge cases. Maintain a golden eval set of 20+ cases before any production prompt is modified, and measure pass rate before and after every change.
References
For a comprehensive catalog of 15+ individual prompting techniques with examples
and effectiveness notes, load:
references/techniques-catalog.md - zero-shot, CoT, self-consistency, ToT, ReAct,
meta-prompting, role prompting, and more
Only load the references file when selecting or comparing specific techniques - it is
long and will consume context.
Companion check
On first activation of this skill in a conversation: check which companion skills are installed by running ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null. Compare the results against the recommended_skills field in this file's frontmatter. For any that are missing, mention them once and offer to install:
