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kbwen / karpathy-principles

Behavioral guidelines to reduce common LLM coding mistakes — Think Before Coding, Simplicity First, Surgical Changes, Goal-Driven Execution.

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Karpathy Coding Principles

Derived from Andrej Karpathy's observations on LLM coding pitfalls.

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

When to Apply

  • Classification: quick-win, feature, architecture-change, hotfix
  • Phase: /plan (assumption surfacing), /implement (simplicity + surgical), /review (scope audit)
  • Trigger: All non-trivial coding tasks — this is a behavioral baseline, not a domain skill

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.

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.

Self-check: "Would a senior engineer say this is overcomplicated?" If yes, simplify.

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.

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.

Checklist

During /plan:

  • [ ] Assumptions stated explicitly before proposing solution
  • [ ] Ambiguities surfaced — multiple interpretations presented if they exist
  • [ ] Simplest viable approach chosen (justify if not the simplest)

During /implement:

  • [ ] No features beyond what was asked
  • [ ] No abstractions for single-use code
  • [ ] Every changed line traces to the user's request
  • [ ] Pre-existing code left alone unless directly required
  • [ ] Success criteria defined before implementation begins

During /review:

  • [ ] Diff contains only requested changes — no drive-by refactoring
  • [ ] Code is not overcomplicated — could a simpler version work?
  • [ ] Orphaned imports/variables from THIS change are cleaned up
  • [ ] Pre-existing dead code mentioned but not deleted

Code Simplification Checklist

When reviewing or refactoring touched lines, apply Chesterton's Fence — understand WHY before removing:

  • [ ] Deep nesting (>3 levels) → extract to named functions
  • [ ] Long functions (>50 lines) → split by responsibility
  • [ ] Poor naming → rename to reveal intent
  • [ ] Speculative abstractions → remove if only one caller exists
  • [ ] Duplicate logic → extract only if 3+ occurrences (not 2)

Simplification rules:

  • Preserve behavior exactly — simplification is NOT a feature change
  • Fewer lines is not always simpler — a 1-line nested ternary is worse than a 5-line if/else
  • Separate simplification commits from feature commits — never mix

Heading-Scoped Read Note

For phase-entry loading, read only:

  • When to Apply
  • Checklist
  • Code Simplification Checklist

Load numbered principle sections (## 1–## 4), Common Rationalizations, Anti-Patterns, and References on full read or cache miss only.

Common Rationalizations

RationalizationReality
"It works, that's good enough"Working code that's unreadable or architecturally wrong creates debt that compounds.
"We'll clean it up later"Later never comes. The current phase is the quality gate — use it.
"I'm confident about this approach"Confidence is not evidence. State your assumptions explicitly or verify against docs.
"This abstraction might be useful later"Don't preserve speculative abstractions. If there's only one caller, inline it.
"I'll just quickly improve this unrelated code too"Unscoped changes create noisy diffs and obscure the actual intent. Touch only what you must.
"The tests pass, so it's good"Tests are necessary but not sufficient. They don't catch architecture problems, security issues, or readability.

Anti-Patterns

  • Silent assumption: Picking one interpretation without surfacing alternatives
  • Speculative flexibility: Adding config/abstraction layers "for the future"
  • Drive-by cleanup: "Improving" adjacent code that wasn't part of the request
  • Vague completion: Claiming "done" without verifiable success criteria
  • Rationalizing shortcuts: Using plausible-sounding excuses to skip verification steps

References