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.

Vendored from addyosmani/agent-skills · skills/code-simplification/SKILL.md, MIT License · Copyright (c) 2025 Addy Osmani.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

HarnessFlow precedence (read this first)

A HarnessFlow workflow invokes this skill from its post-implementation review step when the request header is simplify: local — see _lib/review_skills.md (resolved via Pack Path Resolution) for how it is launched. Everything below the next heading is upstream text. Where it conflicts with the pack, the pack wins:

You do apply your edits to the working tree (that is this skill's job — it is the write step that /code-review or code-review-and-quality later reads). Report what you changed under the output label [simplify].

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.

// 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:

Naming and readability:

Redundancy:

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

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