| name | code-simplification |
| description | Simplifies code for clarity. Use when refactoring code for clarity without changing behavior. Use when code works but is harder to read, maintain, or extend than it should be. Use when reviewing code that has accumulated unnecessary complexity. 사용자가 "단순화해", "깔끔하게 만들어", "리팩토링", "/code-simplify"라고 할 때 트리거. 동작은 보존하고 가독성·유지보수성만 개선.
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Code Simplification
진입점: Codex 용. Claude Code 는 내장 /simplify 가 우선이므로 이 skill 을 별도 배선하지 않는다 (issue #1038 결정).
Inspired by the Claude Code Simplifier plugin. Adapted here as a model-agnostic, process-driven skill for any AI coding agent.
Overview
Simplify code by reducing complexity while preserving exact behavior. The goal is not fewer lines — it's code that is easier to read, understand, modify, and debug. Every simplification must pass a simple test: "Would a new team member understand this faster than the original?"
When to Use
- After a feature is working and tests pass, but the implementation feels heavier than it needs to be
- During code review when readability or complexity issues are flagged
- When you encounter deeply nested logic, long functions, or unclear names
- When refactoring code written under time pressure
- When consolidating related logic scattered across files
- After merging changes that introduced duplication or inconsistency
When NOT to use:
- Code is already clean and readable — don't simplify for the sake of it
- You don't understand what the code does yet — comprehend before you simplify
- The code is performance-critical and the "simpler" version would be measurably slower
- You're about to rewrite the module entirely — simplifying throwaway code wastes effort
The Five Principles
1. Preserve Behavior Exactly
Don't change what the code does — only how it expresses it. All inputs, outputs, side effects, error behavior, and edge cases must remain identical. If you're not sure a simplification preserves behavior, don't make it.
ASK BEFORE EVERY CHANGE:
→ Does this produce the same output for every input?
→ Does this maintain the same error behavior?
→ Does this preserve the same side effects and ordering?
→ Do all existing tests still pass without modification?
2. Follow Project Conventions
Simplification means making code more consistent with the codebase, not imposing external preferences. Before simplifying:
1. Read CLAUDE.md / project conventions
2. Study how neighboring code handles similar patterns
3. Match the project's style for:
- Import ordering and module system
- Function declaration style
- Naming conventions
- Error handling patterns
- Type annotation depth
Simplification that breaks project consistency is not simplification — it's churn.
3. Prefer Clarity Over Cleverness
Explicit code is better than compact code when the compact version requires a mental pause to parse.
const label = isNew ? 'New' : isUpdated ? 'Updated' : isArchived ? 'Archived' : 'Active';
function getStatusLabel(item: Item): string {
if (item.isNew) return 'New';
if (item.isUpdated) return 'Updated';
if (item.isArchived) return 'Archived';
return 'Active';
}
const result = items.reduce((acc, item) => ({
...acc,
[item.id]: { ...acc[item.id], count: (acc[item.id]?.count ?? 0) + 1 }
}), {});
const countById = new Map<string, number>();
for (const item of items) {
countById.set(item.id, (countById.get(item.id) ?? 0) + 1);
}
4. Maintain Balance
Simplification has a failure mode: over-simplification. Watch for these traps:
- Inlining too aggressively — removing a helper that gave a concept a name makes the call site harder to read
- Combining unrelated logic — two simple functions merged into one complex function is not simpler
- Removing "unnecessary" abstraction — some abstractions exist for extensibility or testability, not complexity
- Optimizing for line count — fewer lines is not the goal; easier comprehension is
5. Scope to What Changed
Default to simplifying recently modified code. Avoid drive-by refactors of unrelated code unless explicitly asked to broaden scope. Unscoped simplification creates noise in diffs and risks unintended regressions.
The Simplification Process
Step 1: Understand Before Touching (Chesterton's Fence)
Before changing or removing anything, understand why it exists. This is Chesterton's Fence: if you see a fence across a road and don't understand why it's there, don't tear it down. First understand the reason, then decide if the reason still applies.
BEFORE SIMPLIFYING, ANSWER:
- What is this code's responsibility?
- What calls it? What does it call?
- What are the edge cases and error paths?
- Are there tests that define the expected behavior?
- Why might it have been written this way? (Performance? Platform constraint? Historical reason?)
- Check git blame: what was the original context for this code?
If you can't answer these, you're not ready to simplify. Read more context first.
Step 2: Identify Simplification Opportunities
Scan for these patterns — each one is a concrete signal, not a vague smell:
Structural complexity:
| Pattern | Signal | Simplification |
|---|
| Deep nesting (3+ levels) | Hard to follow control flow | Extract conditions into guard clauses or helper functions |
| Long functions (50+ lines) | Multiple responsibilities | Split into focused functions with descriptive names |
| Nested ternaries | Requires mental stack to parse | Replace with if/else chains, switch, or lookup objects |
| Boolean parameter flags | doThing(true, false, true) | Replace with options objects or separate functions |
| Repeated conditionals | Same if check in multiple places | Extract to a well-named predicate function |
Naming and readability:
| Pattern | Signal | Simplification |
|---|
| Generic names | data, result, temp, val, item | Rename to describe the content: userProfile, validationErrors |
| Abbreviated names | usr, cfg, btn, evt | Use full words unless the abbreviation is universal (id, url, api) |
| Misleading names | Function named get that also mutates state | Rename to reflect actual behavior |
| Comments explaining "what" | // increment counter above count++ | Delete the comment — the code is clear enough |
| Comments explaining "why" | // Retry because the API is flaky under load | Keep these — they carry intent the code can't express |
Redundancy:
| Pattern | Signal | Simplification |
|---|
| Duplicated logic | Same 5+ lines in multiple places | Extract to a shared function |
| Dead code | Unreachable branches, unused variables, commented-out blocks | Remove (after confirming it's truly dead) |
| Unnecessary abstractions | Wrapper that adds no value | Inline the wrapper, call the underlying function directly |
| Over-engineered patterns | Factory-for-a-factory, strategy-with-one-strategy | Replace with the simple direct approach |
| Redundant type assertions | Casting to a type that's already inferred | Remove the assertion |
Step 3: Apply Changes Incrementally
Make one simplification at a time. Run tests after each change. Submit refactoring changes separately from feature or bug fix changes. A PR that refactors and adds a feature is two PRs — split them.
FOR EACH SIMPLIFICATION:
1. Make the change
2. Run the test suite
3. If tests pass → commit (or continue to next simplification)
4. If tests fail → revert and reconsider
Avoid batching multiple simplifications into a single untested change. If something breaks, you need to know which simplification caused it.
The Rule of 500: If a refactoring would touch more than 500 lines, invest in automation (codemods, sed scripts, AST transforms) rather than making the changes by hand. Manual edits at that scale are error-prone and exhausting to review.
Step 4: Verify the Result
After all simplifications, step back and evaluate the whole:
COMPARE BEFORE AND AFTER:
- Is the simplified version genuinely easier to understand?
- Did you introduce any new patterns inconsistent with the codebase?
- Is the diff clean and reviewable?
- Would a teammate approve this change?
If the "simplified" version is harder to understand or review, revert. Not every simplification attempt succeeds.
Language-Specific Guidance / Common Rationalizations
언어별 예제(TS/JS·Python·React)와 흔한 합리화 반론표는 reference.md 로
분리했다 (progressive disclosure — issue #1039).
Red Flags
- Simplification that requires modifying tests to pass (you likely changed behavior)
- "Simplified" code that is longer and harder to follow than the original
- Renaming things to match your preferences rather than project conventions
- Removing error handling because "it makes the code cleaner"
- Simplifying code you don't fully understand
- Batching many simplifications into one large, hard-to-review commit
- Refactoring code outside the scope of the current task without being asked
Verification
After completing a simplification pass:
