Shadcn ui

shadcn/ui Component Development

Contents

• CLI Commands - Installing and adding components
• Quick Reference - cn(), basic CVA pattern
• Component Anatomy - Props typing, asChild, data-slot
• Component Patterns - Compound components
• Styling Techniques - CVA variants, modern CSS selectors, accessibility states
• Decision Tables - When to use CVA, compound components, asChild, Context
• Common Patterns - Form elements, dialogs, sidebars
• Reference Files - Full implementations and advanced patterns

CLI Commands

Initialize shadcn/ui

npx shadcn@latest init

This creates a components.json configuration file and sets up:

• Tailwind CSS configuration
• CSS variables for theming
• cn() utility function
• Required dependencies

Add Components

# Add a single component
npx shadcn@latest add button

# Add multiple components
npx shadcn@latest add button card dialog

# Add all available components
npx shadcn@latest add --all

Important: The package name changed in 2024:

• Old (deprecated): npx shadcn-ui@latest add
• Current: npx shadcn@latest add

Common Options

• -y, --yes - Skip confirmation prompt
• -o, --overwrite - Overwrite existing files
• -c, --cwd <cwd> - Set working directory
• --src-dir - Use src directory structure

Gates (CLI and file changes)

Run these in order before init / add (skip only when you are not running the CLI—e.g. copying snippets from this skill):

1. Working directory: Pass: pwd and package.json at that path identify the app root that should receive components/ and components.json (use -c <cwd> if the shell is elsewhere).
2. After init: Pass: components.json exists at that app root (or the documented path for your monorepo layout).
3. Before --overwrite: Pass: you can list which tracked files will be replaced, or version control shows the change is intentional and recoverable.

Quick Reference

cn() Utility

import { clsx, type ClassValue } from "clsx"
import { twMerge } from "tailwind-merge"

export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs))
}

Basic CVA Pattern

import { cva, type VariantProps } from "class-variance-authority"

const buttonVariants = cva(
  "base-classes-applied-to-all-variants",
  {
    variants: {
      variant: {
        default: "bg-primary text-primary-foreground",
        outline: "border bg-background",
      },
      size: {
        sm: "h-8 px-3",
        lg: "h-10 px-6",
      },
    },
    defaultVariants: {
      variant: "default",
      size: "sm",
    },
  }
)

function Button({
  variant,
  size,
  className,
  ...props
}: React.ComponentProps<"button"> & VariantProps<typeof buttonVariants>) {
  return (
    <button
      className={cn(buttonVariants({ variant, size }), className)}
      {...props}
    />
  )
}

export { Button, buttonVariants }

Component Anatomy

Props Typing Patterns

// HTML elements
function Component({ className, ...props }: React.ComponentProps<"div">) {
  return <div className={cn("base-classes", className)} {...props} />
}

// Radix primitives
function Component({ className, ...props }: React.ComponentProps<typeof RadixPrimitive.Root>) {
  return <RadixPrimitive.Root className={cn("base-classes", className)} {...props} />
}

// With CVA variants
function Component({
  variant, size, className, ...props
}: React.ComponentProps<"button"> & VariantProps<typeof variants>) {
  return <button className={cn(variants({ variant, size }), className)} {...props} />
}

asChild Pattern

Enables polymorphic rendering via @radix-ui/react-slot:

import { Slot } from "@radix-ui/react-slot"

function Button({
  asChild = false,
  className,
  variant,
  size,
  ...props
}: React.ComponentProps<"button"> & VariantProps<typeof buttonVariants> & { asChild?: boolean }) {
  const Comp = asChild ? Slot : "button"
  return (
    <Comp
      data-slot="button"
      className={cn(buttonVariants({ variant, size }), className)}
      {...props}
    />
  )
}

Usage:

<Button>Click me</Button>                           // Renders <button>
<Button asChild><a href="/home">Home</a></Button>   // Renders <a> with button styling
<Button asChild><Link href="/dash">Dash</Link></Button>  // Works with Next.js Link

data-slot Attributes

Every component includes data-slot for CSS targeting:

function Card({ ...props }) { return <div data-slot="card" {...props} /> }
function CardHeader({ ...props }) { return <div data-slot="card-header" {...props} /> }

CSS/Tailwind targeting:

[data-slot="button"] { /* styles */ }
[data-slot="card"] [data-slot="button"] { /* nested targeting */ }

<div className="[&_[data-slot=button]]:shadow-lg">
  <Button>Automatically styled</Button>
</div>

Conditional layouts with has():

<div
  data-slot="card-header"
  className={cn(
    "grid gap-2",
    "has-data-[slot=card-action]:grid-cols-[1fr_auto]"
  )}
/>

Component Patterns

Compound Components

export { Card, CardHeader, CardTitle, CardDescription, CardContent, CardFooter }

function Card({ className, ...props }: React.ComponentProps<"div">) {
  return (
    <div
      data-slot="card"
      className={cn("bg-card text-card-foreground flex flex-col gap-6 rounded-xl border py-6 shadow-sm", className)}
      {...props}
    />
  )
}

function CardHeader({ className, ...props }: React.ComponentProps<"div">) {
  return <div data-slot="card-header" className={cn("grid gap-2 px-6", className)} {...props} />
}

function CardTitle({ className, ...props }: React.ComponentProps<"div">) {
  return <div data-slot="card-title" className={cn("leading-none font-semibold", className)} {...props} />
}

Styling Techniques

CVA Variants

Multiple dimensions:

const buttonVariants = cva("base-classes", {
  variants: {
    variant: {
      default: "bg-primary text-primary-foreground",
      destructive: "bg-destructive text-white",
      outline: "border bg-background",
      ghost: "hover:bg-accent",
      link: "text-primary underline-offset-4 hover:underline",
    },
    size: {
      default: "h-9 px-4 py-2",
      sm: "h-8 px-3",
      lg: "h-10 px-6",
      icon: "size-9",
    },
  },
  defaultVariants: { variant: "default", size: "default" },
})

Compound variants:

compoundVariants: [
  { variant: "outline", size: "lg", class: "border-2" },
]

Type extraction:

type ButtonVariants = VariantProps<typeof buttonVariants>
// Result: { variant?: "default" | "outline" | ..., size?: "sm" | "lg" | ... }

Modern CSS Selectors in Tailwind

has() selector:

<button className="px-4 has-[>svg]:px-3">  // Adjusts padding when contains icon
<div className="has-data-[slot=action]:grid-cols-[1fr_auto]">  // Conditional layout

Group/peer selectors:

<div className="group" data-state="collapsed">
  <div className="group-data-[state=collapsed]:hidden">Hidden when collapsed</div>
</div>

<button className="peer/menu" data-active="true">Menu</button>
<div className="peer-data-[active=true]/menu:text-accent">Styled when sibling active</div>

Container queries:

<div className="@container/card">
  <div className="@md:flex-row">Responds to container width</div>
</div>

Accessibility States

className={cn(
  // Focus
  "outline-none focus-visible:border-ring focus-visible:ring-ring/50 focus-visible:ring-[3px]",
  // Invalid
  "aria-invalid:border-destructive aria-invalid:ring-destructive/20",
  // Disabled
  "disabled:pointer-events-none disabled:opacity-50",
)}

<span className="sr-only">Close</span>  // Screen reader only

Dark Mode

Semantic tokens adapt automatically:

className="bg-background text-foreground dark:bg-input/30 dark:hover:bg-input/50"

Tokens: bg-background, text-foreground, bg-primary, text-primary-foreground, bg-card, text-card-foreground, border-input, text-muted-foreground

Decision Tables

When to Use CVA

Scenario	Use CVA	Alternative
Multiple visual variants (primary, outline, ghost)	Yes	Plain className
Size variations (sm, md, lg)	Yes	Plain className
Compound conditions (outline + large = thick border)	Yes	Conditional cn()
One-off custom styling	No	className prop
Dynamic colors from props	No	Inline styles or CSS variables

When to Use Compound Components

Scenario	Use Compound	Alternative
Complex UI with multiple semantic parts	Yes	Single component with many props
Optional sections (header, footer)	Yes	Boolean show/hide props
Different styling for each part	Yes	CSS selectors
Shared state between parts	Yes + Context	Props drilling
Simple wrapper with children	No	Single component

When to Use asChild

Scenario	Use asChild	Alternative
Component should work as link or button	Yes	Duplicate component
Need button styles on custom element	Yes	Export variant styles
Integration with routing libraries	Yes	Wrapper components
Always renders same element	No	Standard component

When to Use Context

Scenario	Use Context	Alternative
Deep prop drilling (>3 levels)	Yes	Props
State shared by many siblings	Yes	Lift state up
Plugin/extension architecture	Yes	Props
Simple parent-child communication	No	Props

Common Patterns

Form Input

function Input({ className, type, ...props }: React.ComponentProps<"input">) {
  return (
    <input
      type={type}
      data-slot="input"
      className={cn(
        "h-9 w-full rounded-md border px-3 py-1",
        "outline-none focus-visible:border-ring focus-visible:ring-ring/50 focus-visible:ring-[3px]",
        "aria-invalid:border-destructive aria-invalid:ring-destructive/20",
        "disabled:cursor-not-allowed disabled:opacity-50",
        "placeholder:text-muted-foreground dark:bg-input/30",
        className
      )}
      {...props}
    />
  )
}

Dialog Content

function DialogContent({ children, showCloseButton = true, ...props }) {
  return (
    <DialogPortal>
      <DialogOverlay />
      <DialogPrimitive.Content
        data-slot="dialog-content"
        className={cn(
          "fixed top-[50%] left-[50%] translate-x-[-50%] translate-y-[-50%] w-full max-w-lg",
          "bg-background border rounded-lg p-6 shadow-lg",
          "data-[state=open]:animate-in data-[state=open]:fade-in-0 data-[state=open]:zoom-in-95",
          "data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95",
        )}
        {...props}
      >
        {children}
        {showCloseButton && (
          <DialogPrimitive.Close className="absolute top-4 right-4">
            <XIcon /><span className="sr-only">Close</span>
          </DialogPrimitive.Close>
        )}
      </DialogPrimitive.Content>
    </DialogPortal>
  )
}

Sidebar with Context

function SidebarProvider({ defaultOpen = true, children }) {
  const isMobile = useIsMobile()
  const [open, setOpen] = React.useState(defaultOpen)

  React.useEffect(() => {
    const handleKeyDown = (e: KeyboardEvent) => {
      if (e.key === "b" && (e.metaKey || e.ctrlKey)) {
        e.preventDefault()
        setOpen(o => !o)
      }
    }
    window.addEventListener("keydown", handleKeyDown)
    return () => window.removeEventListener("keydown", handleKeyDown)
  }, [])

  const contextValue = React.useMemo(
    () => ({ state: open ? "expanded" : "collapsed", open, setOpen, isMobile }),
    [open, setOpen, isMobile]
  )

  return (
    <SidebarContext.Provider value={contextValue}>
      <div
        data-slot="sidebar-wrapper"
        style={{ "--sidebar-width": "16rem", "--sidebar-width-icon": "3rem" } as React.CSSProperties}
      >
        {children}
      </div>
    </SidebarContext.Provider>
  )
}

Reference Files

For comprehensive examples and advanced patterns:

• components.md - Full implementations: Button, Card, Badge, Input, Label, Textarea, Dialog
• cva.md - CVA patterns: compound variants, responsive variants, type extraction
• patterns.md - Architectural patterns: compound components, asChild, controlled state, Context, data-slot, has() selectors