Clean Code Style

Behavioral guidelines to reduce common LLM coding mistakes, derived from Andrej Karpathy's observations on LLM coding pitfalls.

Tradeoff: These guidelines bias toward caution over speed. For trivial tasks, use judgment.

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1. Think Before Coding

Don't assume. Don't hide confusion. Surface tradeoffs.

Before implementing:

• State your assumptions explicitly. If uncertain, ask.
• If multiple interpretations exist, present them — don't pick silently.
• If a simpler approach exists, say so. Push back when warranted.
• If something is unclear, stop. Name what's confusing. Ask.

Example: Hidden Assumptions

User: "Add a feature to export user data"

Bad — silently assumes scope, format, fields, and file location:

def export_users(format='json'):
    users = User.query.all()
    with open('users.json', 'w') as f:
        json.dump([u.to_dict() for u in users], f)

Good — surfaces assumptions before writing code:

Before implementing, I need to clarify:
1. Scope: Export all users or filtered subset? (privacy implications)
2. Format: Download file? Background job? API endpoint returning data?
3. Fields: Which user fields? (some might be sensitive)
4. Volume: How many users typically? (affects approach)

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2. Simplicity First

Minimum code that solves the problem. Nothing speculative.

• No features beyond what was asked.
• No abstractions for single-use code.
• No "flexibility" or "configurability" that wasn't requested.
• No error handling for impossible scenarios.
• If you write 200 lines and it could be 50, rewrite it.

Ask yourself: "Would a senior engineer say this is overcomplicated?" If yes, simplify.

Example: Over-abstraction

User: "Add a function to calculate discount"

Bad — strategy pattern, config dataclass, 50+ lines for one calculation:

class DiscountStrategy(ABC):
    @abstractmethod
    def calculate(self, amount: float) -> float: ...

class PercentageDiscount(DiscountStrategy): ...
class FixedDiscount(DiscountStrategy): ...

@dataclass
class DiscountConfig:
    strategy: DiscountStrategy
    min_purchase: float = 0.0
    max_discount: float = float('inf')

Good — one function, done:

def calculate_discount(amount: float, percent: float) -> float:
    return amount * (percent / 100)

Add complexity later when you actually need multiple discount types.

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3. Surgical Changes

Touch only what you must. Clean up only your own mess.

When editing existing code:

• Don't "improve" adjacent code, comments, or formatting.
• Don't refactor things that aren't broken.
• Match existing style, even if you'd do it differently.
• If you notice unrelated dead code, mention it — don't delete it.

When your changes create orphans:

• Remove imports/variables/functions that YOUR changes made unused.
• Don't remove pre-existing dead code unless asked.

The test: every changed line should trace directly to the user's request.

Example: Drive-by Refactoring

User: "Fix the bug where empty emails crash the validator"

Bad — adds docstring, improves email validation, adds username validation nobody asked for:

  def validate_user(user_data):
-     # Check email format
-     if not user_data.get('email'):
+     """Validate user data."""
+     email = user_data.get('email', '').strip()
+     if not email:
          raise ValueError("Email required")
-     if '@' not in user_data['email']:
+     if '@' not in email or '.' not in email.split('@')[1]:
          raise ValueError("Invalid email")
+     username = user_data.get('username', '').strip()
+     if len(username) < 3:
+         raise ValueError("Username too short")

Good — only fixes the reported bug:

  def validate_user(user_data):
      # Check email format
-     if not user_data.get('email'):
+     email = user_data.get('email', '')
+     if not email or not email.strip():
          raise ValueError("Email required")
-     if '@' not in user_data['email']:
+     if '@' not in email:
          raise ValueError("Invalid email")

Example: Style Drift

User: "Add logging to the upload function"

Bad — changes quote style, adds type hints, adds docstring, reformats whitespace:

- def upload_file(file_path, destination):
+ def upload_file(file_path: str, destination: str) -> bool:
+     """Upload file to destination with logging."""

Good — adds logging, matches existing single-quote style, touches nothing else:

+ import logging
+ logger = logging.getLogger(__name__)
+
  def upload_file(file_path, destination):
+     logger.info(f'Starting upload: {file_path}')
      try:

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4. Goal-Driven Execution

Define success criteria. Loop until verified.

Transform tasks into verifiable goals:

• "Add validation" -> "Write tests for invalid inputs, then make them pass"
• "Fix the bug" -> "Write a test that reproduces it, then make it pass"
• "Refactor X" -> "Ensure tests pass before and after"

For multi-step tasks, state a brief plan:

1. [Step] -> verify: [check]
2. [Step] -> verify: [check]
3. [Step] -> verify: [check]

Strong success criteria let you loop independently. Weak criteria ("make it work") require constant clarification.

Example: Test-First Verification

User: "The sorting breaks when there are duplicate scores"

Bad — immediately changes sort logic without confirming the bug exists.

Good — reproduce first, then fix:

# 1. Write a test that reproduces the issue
def test_sort_with_duplicate_scores():
    scores = [
        {'name': 'Alice', 'score': 100},
        {'name': 'Bob', 'score': 100},
        {'name': 'Charlie', 'score': 90},
    ]
    result = sort_scores(scores)
    assert result[0]['score'] == 100
    assert result[1]['score'] == 100
    assert result[2]['score'] == 90

# Verify: test fails with inconsistent ordering

# 2. Fix with stable sort
def sort_scores(scores):
    return sorted(scores, key=lambda x: (-x['score'], x['name']))

# Verify: test passes consistently

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Anti-Patterns Summary

| Principle | Anti-Pattern | Fix | |-----------|-------------|-----| | Think Before Coding | Silently assumes format, fields, scope | List assumptions, ask for clarification | | Simplicity First | Strategy pattern for one calculation | One function until complexity is needed | | Surgical Changes | Reformats quotes, adds type hints during bug fix | Only change lines that fix the reported issue | | Goal-Driven | "I'll review and improve the code" | "Write test for bug X -> make it pass -> verify no regressions" |

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Key Insight

The overcomplicated examples aren't obviously wrong — they follow design patterns and best practices. The problem is timing: they add complexity before it's needed.

Good code solves today's problem simply, not tomorrow's problem prematurely.

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These guidelines are working if: fewer unnecessary changes in diffs, fewer rewrites due to overcomplication, and clarifying questions come before implementation rather than after mistakes.