Code simplification

Code Simplification

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

Inputs

Stage: Review — one axis of the parallel fan-out. The orchestrator dispatches this as a fresh, code-cold subagent on the simplification axis (maker≠checker; parallelism.md mech f). It applies its fixes; it does not just report.

Refuse to run unless ALL of these resolve:

• The slice diff — the changed code for the slice under review (the working-tree diff / the files the slice touched). This is the only material in scope. No diff → nothing to simplify → exit clean.
• A green test suite for those files — the behavior oracle. Behavior-preservation is the entire contract (Principle 1); if you cannot run the tests that pin the changed code, you cannot prove you preserved behavior → refuse rather than guess.
• The slice's declared Regression surface — the file set you are allowed to touch. Simplify NEVER edits a file outside it (Principle 5: Scope to What Changed).
• Project conventions — CLAUDE.md / CONTEXT.md and the neighboring code, so simplification converges on the house style instead of imposing a foreign one (Principle 2). Simplification that breaks project consistency is churn, not simplification.

Frozen under this skill (silent-false-green invariant): acceptance.md, the RED/passing tests, and the declared Regression surface are IMMUTABLE here. A "simplification" that edits a test, weakens an assertion, or widens/narrows the surface is gate-erosion → HALT: stop, flip the slice's gate column to you, and surface it. The whole point of this skill is to make the code simpler until the frozen tests still pass — never to change the tests until the simpler code passes.

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.

// UNCLEAR: Dense ternary chain
const label = isNew ? 'New' : isUpdated ? 'Updated' : isArchived ? 'Archived' : 'Active';

// CLEAR: Readable mapping
function getStatusLabel(item: Item): string {
  if (item.isNew) return 'New';
  if (item.isUpdated) return 'Updated';
  if (item.isArchived) return 'Archived';
  return 'Active';
}

// UNCLEAR: Chained reduces with inline logic
const result = items.reduce((acc, item) => ({
  ...acc,
  [item.id]: { ...acc[item.id], count: (acc[item.id]?.count ?? 0) + 1 }
}), {});

// CLEAR: Named intermediate step
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

TypeScript / JavaScript

// SIMPLIFY: Unnecessary async wrapper
// Before
async function getUser(id: string): Promise<User> {
  return await userService.findById(id);
}
// After
function getUser(id: string): Promise<User> {
  return userService.findById(id);
}

// SIMPLIFY: Verbose conditional assignment
// Before
let displayName: string;
if (user.nickname) {
  displayName = user.nickname;
} else {
  displayName = user.fullName;
}
// After
const displayName = user.nickname || user.fullName;

// SIMPLIFY: Manual array building
// Before
const activeUsers: User[] = [];
for (const user of users) {
  if (user.isActive) {
    activeUsers.push(user);
  }
}
// After
const activeUsers = users.filter((user) => user.isActive);

// SIMPLIFY: Redundant boolean return
// Before
function isValid(input: string): boolean {
  if (input.length > 0 && input.length < 100) {
    return true;
  }
  return false;
}
// After
function isValid(input: string): boolean {
  return input.length > 0 && input.length < 100;
}

Python

# SIMPLIFY: Verbose dictionary building
# Before
result = {}
for item in items:
    result[item.id] = item.name
# After
result = {item.id: item.name for item in items}

# SIMPLIFY: Nested conditionals with early return
# Before
def process(data):
    if data is not None:
        if data.is_valid():
            if data.has_permission():
                return do_work(data)
            else:
                raise PermissionError("No permission")
        else:
            raise ValueError("Invalid data")
    else:
        raise TypeError("Data is None")
# After
def process(data):
    if data is None:
        raise TypeError("Data is None")
    if not data.is_valid():
        raise ValueError("Invalid data")
    if not data.has_permission():
        raise PermissionError("No permission")
    return do_work(data)

React / JSX

// SIMPLIFY: Verbose conditional rendering
// Before
function UserBadge({ user }: Props) {
  if (user.isAdmin) {
    return <Badge variant="admin">Admin</Badge>;
  } else {
    return <Badge variant="default">User</Badge>;
  }
}
// After
function UserBadge({ user }: Props) {
  const variant = user.isAdmin ? 'admin' : 'default';
  const label = user.isAdmin ? 'Admin' : 'User';
  return <Badge variant={variant}>{label}</Badge>;
}

// SIMPLIFY: Prop drilling through intermediate components
// Before — consider whether context or composition solves this better.
// This is a judgment call — flag it, don't auto-refactor.

Common Rationalizations

Rationalization	Reality
"It's working, no need to touch it"	Working code that's hard to read will be hard to fix when it breaks. Simplifying now saves time on every future change.
"Fewer lines is always simpler"	A 1-line nested ternary is not simpler than a 5-line if/else. Simplicity is about comprehension speed, not line count.
"I'll just quickly simplify this unrelated code too"	Unscoped simplification creates noisy diffs and risks regressions in code you didn't intend to change. Stay focused.
"The types make it self-documenting"	Types document structure, not intent. A well-named function explains why better than a type signature explains what.
"This abstraction might be useful later"	Don't preserve speculative abstractions. If it's not used now, it's complexity without value. Remove it and re-add when needed.
"The original author must have had a reason"	Maybe. Check git blame — apply Chesterton's Fence. But accumulated complexity often has no reason; it's just the residue of iteration under pressure.
"I'll refactor while adding this feature"	Separate refactoring from feature work. Mixed changes are harder to review, revert, and understand in history.

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:

• All existing tests pass without modification
• Build succeeds with no new warnings
• Linter/formatter passes (no style regressions)
• Each simplification is a reviewable, incremental change
• The diff is clean — no unrelated changes mixed in
• Simplified code follows project conventions (checked against CLAUDE.md or equivalent)
• No error handling was removed or weakened
• No dead code was left behind (unused imports, unreachable branches)
• A teammate or review agent would approve the change as a net improvement

Outputs & handoff contract

Emits: diff — a behavior-preserving simplification of the same changed files, applied to the working tree as a separate refactor: commit, never folded into feature work (Principle 5 / Process Step 3: "Submit refactoring changes separately"). If nothing warrants simplifying, emit no diff and report clean — don't simplify for the sake of it.

Return to the orchestrator (Review fan-out aggregation) exactly one verdict:

• applied — the refactor diff + a one-line summary per simplification, with proof that every existing test passes WITHOUT modification (attach the suite's exit status).
• clean — code is already readable; no change warranted.
• halt — a worthwhile simplification could not be made without changing behavior, OR a frozen artifact would have had to move. Name the file:line and why; do not ship the change.

Invariants on the emitted diff: stays inside the slice's Regression surface; zero test files changed; no error handling removed or weakened; the "after" is genuinely easier to read than the "before" (if not, revert — not every attempt succeeds, per Process Step 4).

STATE.md: this skill writes no STATE.md row of its own. The orchestrator owns the slice's review state and advances it only when every review axis (this skill, code-review, security-and-hardening, performance-optimization) returns non-blocking; a halt from this axis bounces the slice back to Implement (bounded rounds). Stable sections other skills depend on: none beyond the ## Verification checklist below, which is the done-predicate.