Code Quality

Principles

Code Smells Checklist

Naming

• •Booleans: is/has/can/should prefix
• •Functions: verb prefix (get, create, handle, fetch)
• •Descriptive names; avoid abbreviations unless obvious

Functions

• •Single responsibility, <30 lines
• •Max 3 parameters; use parameter object beyond that
• •Minimize side effects
• •Extract complex conditionals into named functions

Complexity

• •Max 2 levels nesting; use early returns
• •Replace conditional chains with lookup maps/polymorphism

Make Invalid States Unrepresentable

• •Use generics / type hints to catch issues at compile-time / static analysis (Python list[str], Java List<String>, TS Array<string>)
• •Use specialized types where invalid inputs are unrepresentable (pydantic BaseModel with dict[str, str] over raw str, typed keys over string constants)
• •No any in TypeScript (use unknown); no force unwraps in Swift (unless provably safe)
• •Use Optional / Option for null safety -- never return bare None/null when absence is possible
• •Validate early at boundaries, convert to constrained types, pass constrained types downstream
• •Leverage utility types: Pick, Omit, Partial, NonNullable
• •Priority: compile-time > static analysis > runtime for catching errors

Anti-Patterns

Code

• •Premature abstraction -- wait for 2+ concrete implementations
• •God objects -- split by responsibility
• •Magic values -- use named constants
• •Swallowed exceptions -- handle meaningfully or propagate
• •Commented-out code -- delete it, git has history

Process

• •Large PRs -- keep small and focused
• •Skipping tests -- costs more later
• •Vague commits -- use fix: prevent null pointer in user lookup
• •TODOs without context -- include why, when, ticket: // TODO(#123): handle rate limiting

Style Defaults

Naming conventions: JS/TS/Swift = camelCase, Python/Rust/Go = snake_case, Types = PascalCase, Constants = SCREAMING_SNAKE_CASE

Style Guides by Language

See each language skill for detailed naming and practice rules.

Import order (separated by blank lines): 1. Standard library, 2. Third-party, 3. Local modules

Lint Priority Triage

Safe auto-fixes: prettier --write ., eslint --fix . Manual fixes needed: type annotations, logic errors, missing error handling, accessibility

Refactoring Decision Framework

• •Early returns over nested conditionals
• •Parameter objects when >3 params
• •Lookup maps over conditional chains
• •Extract function when a block needs a comment to explain intent
• •Typed errors over generic catch-all

Performance (Profile First)

React/Next.js: React.memo, useMemo, code splitting, virtual scrolling Database: Index frequently queried fields, batch queries (N+1), pagination API: SWR/React Query caching, debounce/throttle, parallel requests Bundle: Tree-shake, dynamic imports, route-level code splitting

Dead Code Removal

• •Unused imports, unreachable code, unused variables
• •Run tsc --noEmit and check lint warnings

Measurement Tools