fast-next-template/frontend/docs/design-system/08-ai-guidelines.md

AI Code Generation Guidelines

For AI Assistants: This document contains strict rules for generating code in the FastNext Template project. Follow these rules to ensure generated code matches the design system perfectly.

---

🎯 Core Rules

ALWAYS Do

1. ✅ Import from @/components/ui/*

   import { Button } from '@/components/ui/button';
   import { Card, CardHeader, CardTitle, CardContent } from '@/components/ui/card';
   

2. ✅ Use semantic color tokens

   className="bg-primary text-primary-foreground"
   className="text-destructive"
   className="bg-muted text-muted-foreground"
   

3. ✅ Use cn() utility for className merging

   import { cn } from '@/lib/utils';
   
   className={cn("base-classes", conditional && "conditional-classes", className)}
   

4. ✅ Follow spacing scale (multiples of 4: 0, 1, 2, 3, 4, 6, 8, 12, 16)

   className="p-4 space-y-6 mb-8"
   

5. ✅ Add accessibility attributes

   <Label htmlFor="email">Email</Label>
   <Input
     id="email"
     aria-invalid={!!errors.email}
     aria-describedby={errors.email ? 'email-error' : undefined}
   />
   

6. ✅ Use component variants

   <Button variant="destructive">Delete</Button>
   <Alert variant="destructive">Error message</Alert>
   

7. ✅ Compose from shadcn/ui primitives

   // Don't create custom card components
   // Use Card + CardHeader + CardTitle + CardContent
   

8. ✅ Use mobile-first responsive design

   className="text-2xl sm:text-3xl lg:text-4xl"
   className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3"
   

---

NEVER Do

1. ❌ NO arbitrary colors

   // ❌ WRONG
   className="bg-blue-500 text-white"
   
   // ✅ CORRECT
   className="bg-primary text-primary-foreground"
   

2. ❌ NO arbitrary spacing values

   // ❌ WRONG
   className="p-[13px] mb-[17px]"
   
   // ✅ CORRECT
   className="p-4 mb-4"
   

3. ❌ NO inline styles

   // ❌ WRONG
   style={{ margin: '10px', color: '#3b82f6' }}
   
   // ✅ CORRECT
   className="m-4 text-primary"
   

4. ❌ NO custom CSS classes (use Tailwind utilities)

   // ❌ WRONG
   <div className="my-custom-class">
   
   // ✅ CORRECT
   <div className="flex items-center justify-between p-4">
   

5. ❌ NO mixing component libraries

   // ❌ WRONG - Don't use Material-UI, Ant Design, etc.
   import { Button } from '@mui/material';
   
   // ✅ CORRECT - Only shadcn/ui
   import { Button } from '@/components/ui/button';
   

6. ❌ NO skipping accessibility

   // ❌ WRONG
   <button><X /></button>
   
   // ✅ CORRECT
   <Button size="icon" aria-label="Close">
     <X className="h-4 w-4" />
   </Button>
   

7. ❌ NO creating custom variants without CVA

   // ❌ WRONG
   <Button className={type === 'danger' ? 'bg-red-500' : 'bg-blue-500'}>
   
   // ✅ CORRECT
   <Button variant="destructive">Delete</Button>
   

---

📐 Layout Patterns

Page Container

<div className="container mx-auto px-4 py-8">
  <div className="max-w-4xl mx-auto space-y-6">
    {/* Content */}
  </div>
</div>

Dashboard Grid

<div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-6">
  {items.map(item => <Card key={item.id}>...</Card>)}
</div>

Form Layout

<Card className="max-w-md mx-auto">
  <CardHeader>
    <CardTitle>Form Title</CardTitle>
  </CardHeader>
  <CardContent>
    <form className="space-y-4">
      {/* Form fields */}
    </form>
  </CardContent>
</Card>

Centered Content

<div className="max-w-2xl mx-auto px-4">
  {/* Readable content width */}
</div>

---

🧩 Component Templates

Custom Component Template

import { cn } from '@/lib/utils';
import { Card } from '@/components/ui/card';

interface MyComponentProps {
  variant?: 'default' | 'compact';
  className?: string;
  children: React.ReactNode;
}

export function MyComponent({
  variant = 'default',
  className,
  children
}: MyComponentProps) {
  return (
    <Card className={cn(
      "p-4", // base styles
      variant === 'compact' && "p-2",
      className // allow overrides
    )}>
      {children}
    </Card>
  );
}

Component with CVA (class-variance-authority)

import { cva, type VariantProps } from 'class-variance-authority';
import { cn } from '@/lib/utils';

const componentVariants = cva(
  "base-classes-here", // base
  {
    variants: {
      variant: {
        default: "bg-primary text-primary-foreground",
        destructive: "bg-destructive text-destructive-foreground",
      },
      size: {
        sm: "h-8 px-3 text-xs",
        default: "h-10 px-4 text-sm",
        lg: "h-12 px-6 text-base",
      },
    },
    defaultVariants: {
      variant: "default",
      size: "default",
    },
  }
);

interface ComponentProps
  extends React.HTMLAttributes<HTMLDivElement>,
    VariantProps<typeof componentVariants> {}

export function Component({ variant, size, className, ...props }: ComponentProps) {
  return (
    <div className={cn(componentVariants({ variant, size, className }))} {...props} />
  );
}

---

📝 Form Pattern Template

import { useForm } from 'react-hook-form';
import { zodResolver } from '@hookform/resolvers/zod';
import { z } from 'zod';
import { Button } from '@/components/ui/button';
import { Input } from '@/components/ui/input';
import { Label } from '@/components/ui/label';
import { Alert } from '@/components/ui/alert';

const formSchema = z.object({
  email: z.string().email('Invalid email address'),
  password: z.string().min(8, 'Password must be at least 8 characters'),
});

type FormData = z.infer<typeof formSchema>;

export function MyForm() {
  const form = useForm<FormData>({
    resolver: zodResolver(formSchema),
    defaultValues: {
      email: '',
      password: '',
    },
  });

  const onSubmit = async (data: FormData) => {
    // Handle submission
  };

  return (
    <form onSubmit={form.handleSubmit(onSubmit)} className="space-y-4">
      {/* Email Field */}
      <div className="space-y-2">
        <Label htmlFor="email">Email</Label>
        <Input
          id="email"
          type="email"
          {...form.register('email')}
          aria-invalid={!!form.formState.errors.email}
          aria-describedby={form.formState.errors.email ? 'email-error' : undefined}
        />
        {form.formState.errors.email && (
          <p id="email-error" className="text-sm text-destructive">
            {form.formState.errors.email.message}
          </p>
        )}
      </div>

      {/* Submit Button */}
      <Button type="submit" disabled={form.formState.isSubmitting}>
        {form.formState.isSubmitting ? 'Submitting...' : 'Submit'}
      </Button>
    </form>
  );
}

---

🎨 Color Token Reference

Always use these semantic tokens:

Token	Usage
bg-primary text-primary-foreground	Primary buttons, CTAs
bg-secondary text-secondary-foreground	Secondary actions
bg-destructive text-destructive-foreground	Delete, errors
bg-muted text-muted-foreground	Disabled states
bg-accent text-accent-foreground	Hover states
bg-card text-card-foreground	Card backgrounds
text-foreground	Body text
text-muted-foreground	Secondary text
border-border	Borders
ring-ring	Focus rings

---

📏 Spacing Reference

Use these spacing values (multiples of 4px):

Class	Value	Pixels	Usage
2	0.5rem	8px	Tight spacing
4	1rem	16px	Standard spacing
6	1.5rem	24px	Section spacing
8	2rem	32px	Large gaps
12	3rem	48px	Section dividers
16	4rem	64px	Page sections

---

🔑 Decision Trees

When to use Grid vs Flex?

Need equal-width columns? → Use Grid
  className="grid grid-cols-3 gap-6"

Need flexible item sizes? → Use Flex
  className="flex gap-4"

Need 2D layout (rows + columns)? → Use Grid
  className="grid grid-cols-2 grid-rows-3 gap-4"

Need 1D layout (single row OR column)? → Use Flex
  className="flex flex-col gap-4"

When to use Margin vs Padding?

Spacing between sibling elements? → Use gap or space-y
  className="flex gap-4"
  className="space-y-4"

Internal element spacing? → Use padding
  className="p-4"

External element spacing? → Avoid margins, use parent gap
  // ❌ Child with margin
  <div className="mb-4">

  // ✅ Parent with gap
  <div className="space-y-4">

---

🚨 Common Mistakes to Avoid

❌ Mistake 1: Hardcoding colors

// ❌ WRONG
<div className="bg-red-500 text-white">Error</div>

// ✅ CORRECT
<Alert variant="destructive">Error message</Alert>

❌ Mistake 2: Arbitrary spacing

// ❌ WRONG
<div className="p-[15px] mb-[23px]">

// ✅ CORRECT
<div className="p-4 mb-6">

❌ Mistake 3: Missing accessibility

// ❌ WRONG
<input type="email" />

// ✅ CORRECT
<Label htmlFor="email">Email</Label>
<Input id="email" type="email" />

❌ Mistake 4: Creating custom components unnecessarily

// ❌ WRONG - Custom component for simple composition
function MyCard({ title, children }) {
  return <div className="card">{children}</div>;
}

// ✅ CORRECT - Use shadcn/ui primitives
<Card>
  <CardHeader>
    <CardTitle>{title}</CardTitle>
  </CardHeader>
  <CardContent>{children}</CardContent>
</Card>

❌ Mistake 5: Not using cn() utility

// ❌ WRONG
<div className={`base-class ${isActive ? 'active-class' : ''} ${className}`}>

// ✅ CORRECT
<div className={cn("base-class", isActive && "active-class", className)}>

---

📚 Reference Documentation

Before generating code, check these resources:

1. Quick Start - Essential patterns
2. Components - All shadcn/ui components
3. Layouts - Layout patterns
4. Spacing - Spacing rules
5. Forms - Form patterns
6. Reference - Quick lookup tables

---

✅ Code Generation Checklist

Before outputting code, verify:

• All imports from @/components/ui/*
• Using semantic color tokens (no bg-blue-500)
• Using spacing scale (multiples of 4)
• Using cn() for className merging
• Accessibility attributes included
• Mobile-first responsive design
• Composing from shadcn/ui primitives
• Following established patterns from docs
• No inline styles
• No arbitrary values

---

🤖 AI Assistant Configuration

For Claude Code / Cursor

Add this to your project context:

When generating React/Next.js components:
1. Always import from @/components/ui/*
2. Use semantic tokens (bg-primary, text-destructive)
3. Use cn() utility for classNames
4. Follow spacing scale (4, 8, 12, 16, 24, 32)
5. Add accessibility (labels, ARIA)
6. Use component variants (variant="destructive")
7. Reference: /docs/design-system/08-ai-guidelines.md

For GitHub Copilot

Add to .github/copilot-instructions.md:

# Component Guidelines

- Import from @/components/ui/*
- Use semantic colors: bg-primary, text-destructive
- Spacing: multiples of 4 (p-4, mb-6, gap-8)
- Use cn() for className merging
- Add accessibility attributes
- See /docs/design-system/08-ai-guidelines.md

---

📊 Examples

✅ Good Component (AI Generated)

import { cn } from '@/lib/utils';
import { Card, CardHeader, CardTitle, CardContent } from '@/components/ui/card';
import { Button } from '@/components/ui/button';

interface DashboardCardProps {
  title: string;
  value: string;
  trend?: 'up' | 'down';
  className?: string;
}

export function DashboardCard({ title, value, trend, className }: DashboardCardProps) {
  return (
    <Card className={cn("p-6", className)}>
      <CardHeader>
        <CardTitle className="text-sm font-medium text-muted-foreground">
          {title}
        </CardTitle>
      </CardHeader>
      <CardContent>
        <div className="text-2xl font-bold">{value}</div>
        {trend && (
          <p className={cn(
            "text-xs",
            trend === 'up' && "text-green-600",
            trend === 'down' && "text-destructive"
          )}>
            {trend === 'up' ? '↑' : '↓'} Trend
          </p>
        )}
      </CardContent>
    </Card>
  );
}

Why it's good:

• ✅ Imports from @/components/ui/*
• ✅ Uses semantic tokens
• ✅ Uses cn() utility
• ✅ Follows spacing scale
• ✅ Composes from shadcn/ui primitives
• ✅ TypeScript interfaces
• ✅ Allows className override

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🎓 Learning Path for AI

1. Read Quick Start - Essential patterns
2. Read this document - Rules and templates
3. Reference Component Guide - All components
4. Check Reference Tables - Token lookups

With these guidelines, you can generate code that perfectly matches the design system. Always prioritize consistency over creativity.

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Last Updated: November 2, 2025 For AI Assistants: Follow these rules strictly for optimal code generation.