cc-skill-coding-standards

SKILL.md

Coding Standards & Best Practices

Universal coding standards applicable across all projects.

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

// ✅ GOOD: Descriptive names
const marketSearchQuery = 'election'
const isUserAuthenticated = true
const totalRevenue = 1000

// ❌ BAD: Unclear names
const q = 'election'
const flag = true
const x = 1000

Function Naming

// ✅ GOOD: Verb-noun pattern
async function fetchMarketData(marketId: string) { }
function calculateSimilarity(a: number[], b: number[]) { }
function isValidEmail(email: string): boolean { }

// ❌ BAD: Unclear or noun-only
async function market(id: string) { }
function similarity(a, b) { }
function email(e) { }

Immutability Pattern (CRITICAL)

// ✅ ALWAYS use spread operator
const updatedUser = {
  ...user,
  name: 'New Name'
}

const updatedArray = [...items, newItem]

// ❌ NEVER mutate directly
user.name = 'New Name'  // BAD
items.push(newItem)     // BAD

Error Handling

// ✅ 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')
  }
}

// ❌ BAD: No error handling
async function fetchData(url) {
  const response = await fetch(url)
  return response.json()
}

Async/Await Best Practices

// ✅ GOOD: Parallel execution when possible
const [users, markets, stats] = await Promise.all([
  fetchUsers(),
  fetchMarkets(),
  fetchStats()
])

// ❌ BAD: Sequential when unnecessary
const users = await fetchUsers()
const markets = await fetchMarkets()
const stats = await fetchStats()

Type Safety

// ✅ GOOD: Proper types
interface Market {
  id: string
  name: string
  status: 'active' | 'resolved' | 'closed'
  created_at: Date
}

function getMarket(id: string): Promise<Market> {
  // Implementation
}

// ❌ BAD: Using 'any'
function getMarket(id: any): Promise<any> {
  // Implementation
}

React Best Practices

Component Structure

// ✅ 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>
  )
}

// ❌ BAD: No types, unclear structure
export function Button(props) {
  return <button onClick={props.onClick}>{props.children}</button>
}

Custom Hooks

// ✅ 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

// ✅ GOOD: Proper state updates
const [count, setCount] = useState(0)

// Functional update for state based on previous state
setCount(prev => prev + 1)

// ❌ BAD: Direct state reference
setCount(count + 1)  // Can be stale in async scenarios

Conditional Rendering

// ✅ GOOD: Clear conditional rendering
{isLoading && <Spinner />}
{error && <ErrorMessage error={error} />}
{data && <DataDisplay data={data} />}

// ❌ 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

// ✅ 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'

// ✅ 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

// ✅ 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)

// ❌ 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'

// ✅ GOOD: Memoize expensive computations
const sortedMarkets = useMemo(() => {
  return markets.sort((a, b) => b.volume - a.volume)
}, [markets])

// ✅ GOOD: Memoize callbacks
const handleSearch = useCallback((query: string) => {
  setSearchQuery(query)
}, [])

Lazy Loading

import { lazy, Suspense } from 'react'

// ✅ GOOD: Lazy load heavy components
const HeavyChart = lazy(() => import('./HeavyChart'))

export function Dashboard() {
  return (
    <Suspense fallback={<Spinner />}>
      <HeavyChart />
    </Suspense>
  )
}

Database Queries

// ✅ GOOD: Select only needed columns
const { data } = await supabase
  .from('markets')
  .select('id, name, status')
  .limit(10)

// ❌ 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

// ✅ 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', () => { })

// ❌ BAD: Vague test names
test('works', () => { })
test('test search', () => { })

Code Smell Detection

Watch for these anti-patterns:

1. Long Functions

// ❌ BAD: Function > 50 lines
function processMarketData() {
  // 100 lines of code
}

// ✅ GOOD: Split into smaller functions
function processMarketData() {
  const validated = validateData()
  const transformed = transformData(validated)
  return saveData(transformed)
}

2. Deep Nesting

// ❌ BAD: 5+ levels of nesting
if (user) {
  if (user.isAdmin) {
    if (market) {
      if (market.isActive) {
        if (hasPermission) {
          // Do something
        }
      }
    }
  }
}

// ✅ 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

// ❌ BAD: Unexplained numbers
if (retryCount > 3) { }
setTimeout(callback, 500)

// ✅ 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.

When to Use

This skill is applicable to execute the workflow or actions described in the overview.

Limitations

Use this skill only when the task clearly matches the scope described above.

Do not treat the output as a substitute for environment-specific validation, testing, or expert review.

Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.