Code simplification

Code Simplification

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

Tech Context

Tech is declared in .opencode/harness/rules/tech.md. Each name maps directly to .opencode/harness/tech/<name>/ (e.g. rust → .opencode/harness/tech/rust/, react → .opencode/harness/tech/react/). This skill draws on common/ and <name>/coding-style.md — read them by task in Step 2, not all at once. Inline examples use TypeScript for illustration — apply the underlying pattern in <name>'s idioms, not the literal syntax.

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. Match the project's import ordering, function declaration style, naming, error handling, and type annotation depth rather than your own defaults — the loaded <name>/ and common/ files define what "consistent" means here.

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. If a reader has to stop and decode it, rewrite it — see KISS in common/principles.md and "Obscured intent" in common/code-smells.md for the patterns and fixes.

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 the concrete patterns cataloged in the tech files. Each entry there is a signal, not an automatic verdict — investigate before acting. Read the row matching the task — one or two files, not all of them.

Concern	Where the catalog lives
Deep nesting, long functions, flag args, dead code, duplication, magic numbers, obscured intent	common/code-smells.md (../../tech/common/code-smells.md)
Small functions, do-one-thing, argument count, no side effects, no flag arguments	common/functions.md (../../tech/common/functions.md)
Intention-revealing names, no encodings, side-effect-honest names, one-word-per-concept	common/naming.md (../../tech/common/naming.md)
Self-documenting code first; "why" comments kept, "what" comments deleted	common/comments.md (../../tech/common/comments.md)
DRY/YAGNI/KISS, emergent design, command-query separation	common/principles.md (../../tech/common/principles.md)

Language-specific manifestations (clippy, eslint, ruff rules) and the idiomatic fix for each pattern:

→ <name>/coding-style.md

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

The skill is language-agnostic; the syntax for each simplification (removing redundant async/await, replacing manual array building with filter, dict comprehensions, early-return guard clauses, conditional JSX rendering) is owned by the tech files. Apply <name>/coding-style.md for the target language's idioms and tooling rather than restating them here.

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 AGENTS.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