Expensify Coding Standards

Coding standards for the Expensify App. Each standard is a standalone file in rules/ with reasoning, examples, and applicability conditions.

Categories

Quick Reference

Performance

• PERF-1 — No spread in renderItem
• PERF-2 — Return early before expensive work
• PERF-3 — Use OnyxListItemProvider in renderItem
• PERF-5 — Shallow over deep comparisons
• PERF-6 — Derive state from props
• PERF-7 — Reset via key prop
• PERF-8 — Handle events in handlers
• PERF-9 — No useEffect chains
• PERF-10 — No useEffect parent communication
• PERF-11 — Optimize data selection
• PERF-12 — Prevent memory leaks
• PERF-13 — Hoist iterator-independent calls
• PERF-14 — Use useSyncExternalStore
• PERF-15 — Clean up async Effects
• PERF-16 — Guard double initialization

Consistency

• CONSISTENCY-1 — No platform-specific checks in components
• CONSISTENCY-2 — No magic numbers/strings
• CONSISTENCY-3 — No code duplication
• CONSISTENCY-4 — No unused props
• CONSISTENCY-5 — Justify ESLint disables
• CONSISTENCY-6 — Proper error handling

Clean React Patterns

• CLEAN-REACT-PATTERNS-0 — React Compiler compliance
• CLEAN-REACT-PATTERNS-1 — Composition over configuration
• CLEAN-REACT-PATTERNS-2 — Components own their behavior
• CLEAN-REACT-PATTERNS-3 — Context-free component contracts
• CLEAN-REACT-PATTERNS-4 — No side-effect spaghetti
• CLEAN-REACT-PATTERNS-5 — Keep state narrow

Usage

During development: When writing or modifying src/ files, consult the relevant standard files for detailed conditions, examples, and exceptions.

During review: The code-inline-reviewer agent loads all standards from this directory. See .claude/agents/code-inline-reviewer.md.