learnprompt Skill 13: System Prompt Learning（系统提示学习范式）
Source: https://x.com/karpathy/status/1921368644069765486 "System prompt learning — missing LLM learning paradigm"
Core Principle
The system prompt is a textbook. Write it like one.
Karpathy's insight: there are three learning modes for LLMs (pretrain, finetune, RL) — but there's a fourth that's massively underused: system prompt learning. Explicitly encoding strategy into the system prompt is more sample-efficient than retraining and more reliable than hoping the model figures it out.
Think of it as writing a textbook for the LLM before each task. Not just instructions — strategy with reasoning.
The System Prompt Learning Framework
Good system prompts have three layers (mirroring how humans learn):
Layer 1: EXPOSITION (pretrain equivalent)
→ Background knowledge the model needs
→ Relevant concepts, terminology, context
→ "Here's what you need to know about [domain]"
Layer 2: WORKED EXAMPLES (SFT equivalent)
→ Step-by-step demonstration of correct behavior
→ Explicit reasoning traces
→ "Here's exactly how to handle [situation]"
Layer 3: STRATEGY (RL equivalent)
→ Explicit decision rules
→ Error patterns to avoid
→ "When you see X, do Y because Z"
Building a System Prompt from Scratch
Build a system prompt that teaches an LLM to [TASK] reliably.
Task description: [WHAT THE LLM SHOULD DO]
Current failure mode: [HOW IT CURRENTLY GOES WRONG]
Desired behavior: [EXACTLY WHAT GOOD LOOKS LIKE]
Structure the system prompt with all three learning layers:
Layer 1 — Exposition:
Write 2-3 paragraphs of background knowledge the LLM needs.
Include: key concepts, relevant context, domain vocabulary.
Layer 2 — Worked Examples:
Write 2 complete examples of the task done correctly.
Format: INPUT → [step-by-step reasoning] → OUTPUT
Show the thinking, not just the answer.
Layer 3 — Strategy:
Write explicit decision rules as IF/THEN/BECAUSE statements.
Include: common mistakes to avoid, edge cases to handle, quality checks.
End with: "Before responding, verify: [checklist of 3-5 quality checks]"
Improving an Existing System Prompt
When your current system prompt isn't working well:
Diagnose and improve this system prompt.
Current system prompt:
[PASTE CURRENT PROMPT]
Failure mode I'm seeing:
[DESCRIBE HOW IT'S GOING WRONG]
Example of bad output:
[PASTE BAD EXAMPLE]
Example of good output:
[PASTE GOOD EXAMPLE]
Analysis:
1. What's missing from the exposition layer? (background knowledge gaps)
2. What worked examples should I add?
3. What explicit rules would prevent this failure mode?
4. Is the prompt too restrictive? Too vague? Wrong framing?
Output: improved version of the system prompt with changes annotated.
Strategy Encoding Templates
For coding tasks
SYSTEM PROMPT: [CODING TASK]
You are an expert [LANGUAGE] developer. Follow this exact strategy:
UNDERSTANDING PHASE (always do this first):
- Restate the task in your own words
- List all edge cases you can think of
- Identify the one tricky part
IMPLEMENTATION PHASE:
- Start with the simplest working version
- Add complexity only when simple version fails
- Comment every non-obvious line with WHY
VERIFICATION PHASE (always do this last):
- Trace through your code with one concrete example
- Check: does it handle empty input? Large input? Wrong type?
- Confirm: could a junior dev maintain this?
NEVER:
- Assume the input is well-formed without checking
- Add dependencies without saying why
- Write clever code when simple code works
For analysis tasks
SYSTEM PROMPT: [ANALYSIS TASK]
You are an analytical expert. Follow this strategy:
GROUNDING:
- Always cite specific evidence before making claims
- Confidence levels: CERTAIN / LIKELY / SPECULATIVE — always label which
- If you don't know something, say so explicitly
STRUCTURE:
- Lead with the conclusion, then the evidence
- One claim per paragraph
- Maximum 3 levels of nesting
QUALITY CHECKS before responding:
- [ ] Every claim has evidence?
- [ ] Confidence levels labeled?
- [ ] Would an expert in this field agree with this framing?
- [ ] Am I answering the actual question or a related easier one?
For creative/writing tasks
SYSTEM PROMPT: [WRITING TASK]
Writing strategy for this task:
VOICE:
[Describe the tone, style, what to avoid]
STRUCTURE:
[Describe the expected output format]
QUALITY STANDARD:
A response is good when [describe what success looks like].
A response is bad when [describe common failure modes].
EXAMPLE OF GOOD OUTPUT:
[Paste one example]
EXAMPLE OF BAD OUTPUT (and why):
[Paste one example with annotation]
Prompt Version Control
Track your system prompt iterations like code:
# [PROMPT NAME] — Version History
## v3 (current) — [DATE]
Change: Added explicit "verification phase" checklist
Reason: v2 was skipping edge case checking
Result: Failure rate dropped from ~30% to ~5%
## v2 — [DATE]
Change: Added worked examples section
Reason: v1 was too abstract; model wasn't following the strategy
Result: Moderate improvement
## v1 — [DATE]
Initial version: [PASTE]
The Meta-Prompt (write prompts with an LLM)
Help me write a system prompt for this agent.
Agent task: [WHAT IT SHOULD DO]
I'll be using this with: [CLAUDE / GPT-4 / etc.]
Critical behavior: [WHAT MUST ALWAYS HAPPEN]
Failure modes to prevent: [WHAT GOES WRONG WITHOUT GOOD PROMPTING]
Apply the three-layer system prompt learning framework:
1. Exposition (what the model needs to know)
2. Worked examples (demonstrate correct behavior)
3. Strategy rules (explicit IF/THEN/BECAUSE)
Then: suggest 3 variations I could test to find the best version.
Workflow
属于工作流：反偏见决策（第3步/终点）
| 位置 | 上游 | 下游 |
|---|---|---|
| 第3步（沉淀） | karpathy-understanding-first（验证后） | 沉淀完成，可复用 |
完整链路：llm-simulator → understanding-first → system-prompt-learning
也在日常开发中独立使用——任何时候 Agent 反复犯同一类错，都应该触发本 Skill。
Prompt Contract
Extract a system prompt lesson from this failure/pattern: <DESCRIBE_THE_RECURRING_ERROR>. Produce: 1) Trigger condition — when does this error occur, 2) Correct strategy — step-by-step what the agent should do instead, 3) Anti-patterns — what specifically to avoid, 4) Worked example — a before/after showing the improvement, 5) Concise instruction block (< 200 words) ready to paste into system prompt or SKILL.md.
Verification Checklist
- 触发条件描述具体（不是「有时候」）
- 策略是 step-by-step 的（不是模糊建议）
- 反模式列出了具体的错误做法
- 有 before/after 对比示例
- 指令块 < 200 words，可直接粘贴
- 在新的测试 case 上验证过指令块有效