Coding Standards & Best Practices
Baseline coding conventions applicable across projects.
This skill is the shared floor, not the detailed framework playbook.
- Use
frontend-patternsfor React, state, forms, rendering, and UI architecture. - Use
backend-patternsorapi-designfor repository/service layers, endpoint design, validation, and server-specific concerns. - Use
rules/common/coding-style.mdwhen you need the shortest reusable rule layer instead of a full skill walkthrough.
When to Activate
- Starting a new project or module
- Reviewing code for quality and maintainability
- Refactoring existing code to follow conventions
- Enforcing naming, formatting, or structural consistency
- Setting up linting, formatting, or type-checking rules
- Onboarding new contributors to coding conventions
Scope Boundaries
Activate this skill for:
- descriptive naming
- immutability defaults
- readability, KISS, DRY, and YAGNI enforcement
- error-handling expectations and code-smell review
Do not use this skill as the primary source for:
- React composition, hooks, or rendering patterns
- backend architecture, API design, or database layering
- domain-specific framework guidance when a narrower ECC skill already exists
Code Quality Principles
1. Readability First
- Code is read more than written
- Clear variable and function names
- Self-documenting code preferred over comments
- Consistent formatting
2. KISS (Keep It Simple, Stupid)
- Simplest solution that works
- Avoid over-engineering
- No premature optimization
- Easy to understand > clever code
3. DRY (Don't Repeat Yourself)
- Extract common logic into functions
- Create reusable components
- Share utilities across modules
- Avoid copy-paste programming
4. YAGNI (You Aren't Gonna Need It)
- Don't build features before they're needed
- Avoid speculative generality
- Add complexity only when required
- Start simple, refactor when needed
TypeScript/JavaScript Standards
Variable Naming
// PASS: GOOD: Descriptive names
const marketSearchQuery = 'election'
const isUserAuthenticated = true
const totalRevenue = 1000
// FAIL: BAD: Unclear names
const q = 'election'
const flag = true
const x = 1000
Function Naming
// PASS: GOOD: Verb-noun pattern
async function fetchMarketData(marketId: string) { }
function calculateSimilarity(a: number[], b: number[]) { }
function isValidEmail(email: string): boolean { }
// FAIL: BAD: Unclear or noun-only
async function market(id: string) { }
function similarity(a, b) { }
function email(e) { }
Immutability Pattern (CRITICAL)
// PASS: ALWAYS use spread operator
const updatedUser = {
...user,
name: 'New Name'
}
const updatedArray = [...items, newItem]
// FAIL: NEVER mutate directly
user.name = 'New Name' // BAD
items.push(newItem) // BAD
Error Handling
// PASS: GOOD: Comprehensive error handling
async function fetchData(url: string) {
try {
const response = await fetch(url)
if (!response.ok) {
throw new Error(`HTTP ${response.status}: ${response.statusText}`)
}
return await response.json()
} catch (error) {
console.error('Fetch failed:', error)
throw new Error('Failed to fetch data')
}
}
// FAIL: BAD: No error handling
async function fetchData(url) {
const response = await fetch(url)
return response.json()
}
Async/Await Best Practices
// PASS: GOOD: Parallel execution when possible
const [users, markets, stats] = await Promise.all([
fetchUsers(),
fetchMarkets(),
fetchStats()
])
// FAIL: BAD: Sequential when unnecessary
const users = await fetchUsers()
const markets = await fetchMarkets()
const stats = await fetchStats()
Type Safety
// PASS: GOOD: Proper types
interface Market {
id: string
name: string
status: 'active' | 'resolved' | 'closed'
created_at: Date
}
function getMarket(id: string): Promise<Market> {
// Implementation
}
// FAIL: BAD: Using 'any'
function getMarket(id: any): Promise<any> {
// Implementation
}
React Best Practices
Component Structure
// PASS: GOOD: Functional component with types
interface ButtonProps {
children: React.ReactNode
onClick: () => void
disabled?: boolean
variant?: 'primary' | 'secondary'
}
export function Button({
children,
onClick,
disabled = false,
variant = 'primary'
}: ButtonProps) {
return (
<button
onClick={onClick}
disabled={disabled}
className={`btn btn-${variant}`}
>
{children}
</button>
)
}
// FAIL: BAD: No types, unclear structure
export function Button(props) {
return <button onClick={props.onClick}>{props.children}</button>
}
Custom Hooks
// PASS: GOOD: Reusable custom hook
export function useDebounce<T>(value: T, delay: number): T {
const [debouncedValue, setDebouncedValue] = useState<T>(value)
useEffect(() => {
const handler = setTimeout(() => {
setDebouncedValue(value)
}, delay)
return () => clearTimeout(handler)
}, [value, delay])
return debouncedValue
}
// Usage
const debouncedQuery = useDebounce(searchQuery, 500)
State Management
// PASS: GOOD: Proper state updates
const [count, setCount] = useState(0)
// Functional update for state based on previous state
setCount(prev => prev + 1)
// FAIL: BAD: Direct state reference
setCount(count + 1) // Can be stale in async scenarios
Conditional Rendering
// PASS: GOOD: Clear conditional rendering
{isLoading && <Spinner />}
{error && <ErrorMessage error={error} />}
{data && <DataDisplay data={data} />}
// FAIL: BAD: Ternary hell
{isLoading ? <Spinner /> : error ? <ErrorMessage error={error} /> : data ? <DataDisplay data={data} /> : null}
API Design Standards
REST API Conventions
GET /api/markets # List all markets
GET /api/markets/:id # Get specific market
POST /api/markets # Create new market
PUT /api/markets/:id # Update market (full)
PATCH /api/markets/:id # Update market (partial)
DELETE /api/markets/:id # Delete market
# Query parameters for filtering
GET /api/markets?status=active&limit=10&offset=0
Response Format
// PASS: GOOD: Consistent response structure
interface ApiResponse<T> {
success: boolean
data?: T
error?: string
meta?: {
total: number
page: number
limit: number
}
}
// Success response
return NextResponse.json({
success: true,
data: markets,
meta: { total: 100, page: 1, limit: 10 }
})
// Error response
return NextResponse.json({
success: false,
error: 'Invalid request'
}, { status: 400 })
Input Validation
import { z } from 'zod'
// PASS: GOOD: Schema validation
const CreateMarketSchema = z.object({
name: z.string().min(1).max(200),
description: z.string().min(1).max(2000),
endDate: z.string().datetime(),
categories: z.array(z.string()).min(1)
})
export async function POST(request: Request) {
const body = await request.json()
try {
const validated = CreateMarketSchema.parse(body)
// Proceed with validated data
} catch (error) {
if (error instanceof z.ZodError) {
return NextResponse.json({
success: false,
error: 'Validation failed',
details: error.errors
}, { status: 400 })
}
}
}
File Organization
Project Structure
src/
├── app/ # Next.js App Router
│ ├── api/ # API routes
│ ├── markets/ # Market pages
│ └── (auth)/ # Auth pages (route groups)
├── components/ # React components
│ ├── ui/ # Generic UI components
│ ├── forms/ # Form components
│ └── layouts/ # Layout components
├── hooks/ # Custom React hooks
├── lib/ # Utilities and configs
│ ├── api/ # API clients
│ ├── utils/ # Helper functions
│ └── constants/ # Constants
├── types/ # TypeScript types
└── styles/ # Global styles
File Naming
components/Button.tsx # PascalCase for components
hooks/useAuth.ts # camelCase with 'use' prefix
lib/formatDate.ts # camelCase for utilities
types/market.types.ts # camelCase with .types suffix
Comments & Documentation
When to Comment
// PASS: GOOD: Explain WHY, not WHAT
// Use exponential backoff to avoid overwhelming the API during outages
const delay = Math.min(1000 * Math.pow(2, retryCount), 30000)
// Deliberately using mutation here for performance with large arrays
items.push(newItem)
// FAIL: BAD: Stating the obvious
// Increment counter by 1
count++
// Set name to user's name
name = user.name
JSDoc for Public APIs
/**
* Searches markets using semantic similarity.
*
* @param query - Natural language search query
* @param limit - Maximum number of results (default: 10)
* @returns Array of markets sorted by similarity score
* @throws {Error} If OpenAI API fails or Redis unavailable
*
* @example
* ```typescript
* const results = await searchMarkets('election', 5)
* console.log(results[0].name) // "Trump vs Biden"
* ```
*/
export async function searchMarkets(
query: string,
limit: number = 10
): Promise<Market[]> {
// Implementation
}
Performance Best Practices
Memoization
import { useMemo, useCallback } from 'react'
// PASS: GOOD: Memoize expensive computations
const sortedMarkets = useMemo(() => {
return markets.sort((a, b) => b.volume - a.volume)
}, [markets])
// PASS: GOOD: Memoize callbacks
const handleSearch = useCallback((query: string) => {
setSearchQuery(query)
}, [])
Lazy Loading
import { lazy, Suspense } from 'react'
// PASS: GOOD: Lazy load heavy components
const HeavyChart = lazy(() => import('./HeavyChart'))
export function Dashboard() {
return (
<Suspense fallback={<Spinner />}>
<HeavyChart />
</Suspense>
)
}
Database Queries
// PASS: GOOD: Select only needed columns
const { data } = await supabase
.from('markets')
.select('id, name, status')
.limit(10)
// FAIL: BAD: Select everything
const { data } = await supabase
.from('markets')
.select('*')
Testing Standards
Test Structure (AAA Pattern)
test('calculates similarity correctly', () => {
// Arrange
const vector1 = [1, 0, 0]
const vector2 = [0, 1, 0]
// Act
const similarity = calculateCosineSimilarity(vector1, vector2)
// Assert
expect(similarity).toBe(0)
})
Test Naming
// PASS: GOOD: Descriptive test names
test('returns empty array when no markets match query', () => { })
test('throws error when OpenAI API key is missing', () => { })
test('falls back to substring search when Redis unavailable', () => { })
// FAIL: BAD: Vague test names
test('works', () => { })
test('test search', () => { })
Code Smell Detection
Watch for these anti-patterns:
1. Long Functions
// FAIL: BAD: Function > 50 lines
function processMarketData() {
// 100 lines of code
}
// PASS: GOOD: Split into smaller functions
function processMarketData() {
const validated = validateData()
const transformed = transformData(validated)
return saveData(transformed)
}
2. Deep Nesting
// FAIL: BAD: 5+ levels of nesting
if (user) {
if (user.isAdmin) {
if (market) {
if (market.isActive) {
if (hasPermission) {
// Do something
}
}
}
}
}
// PASS: GOOD: Early returns
if (!user) return
if (!user.isAdmin) return
if (!market) return
if (!market.isActive) return
if (!hasPermission) return
// Do something
3. Magic Numbers
// FAIL: BAD: Unexplained numbers
if (retryCount > 3) { }
setTimeout(callback, 500)
// PASS: GOOD: Named constants
const MAX_RETRIES = 3
const DEBOUNCE_DELAY_MS = 500
if (retryCount > MAX_RETRIES) { }
setTimeout(callback, DEBOUNCE_DELAY_MS)
Remember: Code quality is not negotiable. Clear, maintainable code enables rapid development and confident refactoring.