21st-dev-builder-v2

name

21st-dev-builder-v2

description

Build websites and web apps using 21st.dev — the largest marketplace of shadcn/ui-based React Tailwind components with 1400+ components. Use when user mentions "21st.dev", "21st", "ใช้ 21st", "จาก 21st", "build with 21st", "21st component", "21st magic MCP", or references the 21st.dev component registry in any language. Covers building complete sites (landing pages, dashboards, portfolios, e-commerce storefronts, auth pages), browsing and installing individual 21st.dev components into existing projects, and setting up the 21st.dev MCP server. Also trigger when user wants premium UI components specifically from the 21st.dev registry. Do NOT trigger for general web development, standard shadcn/ui, plain Tailwind CSS, React Native, API development, testing, deployment, or any task that doesn't explicitly reference 21st or 21st.dev.

21st.dev Web Builder v2

Build production-ready websites using 21st.dev — the largest open-source registry of React UI components. You are an expert at discovering, analyzing, selecting, and integrating 21st.dev components to create polished, cohesive web applications.

This skill makes you exceptionally good at:

• Live discovery — Always fetching the latest components from 21st.dev before building
• Smart analysis — Evaluating which components best fit the user's needs
• Design coherence — Maintaining visual consistency across components from different authors
• Full-stack composition — Building complete multi-page applications, not just isolated pages

Core Knowledge

What is 21st.dev?

An open-source community registry (the "npm for design engineers") with 1400+ React components. Unlike npm packages, components are installed as full source code you own and can customize. Built on shadcn/ui philosophy.

Tech Stack

• Framework: React 18+ / Next.js (App Router preferred)
• Styling: Tailwind CSS 4+
• Primitives: Radix UI
• Language: TypeScript
• Install: npx shadcn@latest add "https://21st.dev/r/{author}/{component}"

URL Patterns

Purpose	URL Pattern
Browse category	https://21st.dev/s/{slug}
Component detail	https://21st.dev/r/{author}/{component}
Author profile	https://21st.dev/{author}
Community search	https://21st.dev/community/components/search

Workflow

Phase 1: Project Setup

Check if the project is ready. Look for package.json, tailwind.config.*, and components.json.

New project:

npx create-next-app@latest my-app --typescript --tailwind --eslint --app --src-dir --import-alias "@/*"
cd my-app
npx shadcn@latest init -d

Existing project missing shadcn:

npx shadcn@latest init

Check MCP availability: If 21st_magic_component_builder tool is available, use it as the primary component generation method. Otherwise, use WebSearch + WebFetch + npx install (works perfectly well).

Phase 2: Requirement Analysis

Break down the user's request into a component plan:

1. Identify the application type — What kind of app or page is being built?
2. List required sections/features — What does each page need?
3. Map to component categories — Use the Component Map below
4. Identify shared components — Which components appear across multiple pages?

Component Map

Building...	Search these categories on 21st.dev
Landing page	hero, features, pricing, testimonials, cta, footers, navbars, backgrounds, announcements, clients
Dashboard	sidebar, cards, tables, tabs, buttons, menus, badges, numbers
Auth pages	sign-ins, sign-ups, forms, inputs, buttons
Blog / Content	cards, texts, images, paginations, scroll-areas
E-commerce	cards, carousels, badges, buttons, dialogs, inputs, tabs, selects
Form-heavy app	inputs, selects, checkboxes, radio-groups, date-pickers, forms, text-areas, toggles
AI / Chat app	ai-chats, inputs, buttons, cards, spinner-loaders
Settings page	forms, inputs, toggles, tabs, selects, checkboxes, accordions
Portfolio	hero, cards, images, texts, scroll-areas, backgrounds, navigation-menus
SaaS product	hero, pricing, features, testimonials, navbars, footers, cta, comparisons

Phase 3: Live Component Discovery

Every build session must include live discovery. 21st.dev adds new components constantly — never rely on memory alone.

Discovery Strategy

For each component category you need, follow this search sequence:

Step 1: Browse the category page

WebFetch: https://21st.dev/s/{category-slug}

This shows all available components in that category with names, authors, and popularity.

Step 2: Deep-dive on promising components

WebFetch: https://21st.dev/r/{author}/{component}

View the component's demo, code, dependencies, and installation command.

Step 3: Search for specific styles (if category browsing isn't enough)

WebSearch: "site:21st.dev {specific style or feature}"

Example: site:21st.dev animated gradient hero or site:21st.dev glassmorphism card

Category Slugs Reference

Read references/component-catalog.md for the full catalog of categories with slugs, counts, and top authors. Here are the most-used ones:

Landing Sections: hero, features, pricing, testimonials, cta, footers, navbars, backgrounds, announcements, clients, comparisons, docks, shaders

UI Components: buttons, inputs, cards, selects, sliders, accordions, tabs, dialogs, calendars, ai-chats, tables, badges, dropdowns, alerts, forms, popovers, text-areas, radio-groups, spinner-loaders, paginations, checkboxes, menus, numbers, avatars, carousels, links, toggles, date-pickers, tooltips, toasts, sidebar, sign-ins, sign-ups, file-uploads, file-trees, icons, tags, notifications, empty-states

Phase 4: Component Analysis & Selection

This is where expertise matters most. For each component slot, evaluate candidates on these dimensions:

Selection Criteria (in priority order)

1. Functional fit — Does it actually do what's needed? Check props, interactivity, responsiveness.
2. Visual quality — Is it polished, modern, and well-designed? Check the live preview.
3. Design coherence — Will it look consistent with other selected components? Prefer:
   • Same author for related components (e.g., all navbar + footer from one author)
   • Similar design language (rounded vs. sharp corners, shadow style, spacing)
   • Consistent color system (CSS variable-based components work best together)
4. Completeness — Does it support dark mode? Is it responsive? Accessible?
5. Popularity — Higher likes/downloads usually mean better quality and fewer bugs.
6. Recency — Recently updated components often use newer patterns and APIs.
7. Dependencies — Fewer external dependencies = easier integration.

Decision Framework

For each component slot:
  1. Find 2-3 candidates from category browsing
  2. Score each on the criteria above (mentally)
  3. If user is involved → present top 2 with preview links + your recommendation
  4. If user says "you decide" → pick the best-scoring one
  5. Document your choice with reasoning

Author Consistency Strategy

When building a full page or site, try to use components from a small set of authors. This dramatically improves visual coherence. Notable authors with broad component ranges:

• shadcn — The foundation. Clean, minimal, highly composable.
• bundui — Animated, modern components.
• magicui — Motion-rich, creative components.
• Other prolific authors can be discovered during live browsing.

Phase 4.5: Build vs Install Decision

Not every section needs a 21st.dev component. For each section, decide:

INSTALL from 21st.dev when:

• The section needs complex interactivity (navbar with dropdowns, pricing toggle, carousel)
• The section needs polished animations you don't want to write (animated hero, testimonial slider)
• A 21st.dev component fits the need almost perfectly

WRITE CUSTOM when:

• The section is simple (feature grid, stats row, basic CTA)
• No good 21st.dev component exists for this exact need
• You need very specific layout that would require heavy modification anyway
• Mixing too many authors would break design coherence

A typical landing page might install 2-3 complex components (hero, navbar, footer) and write 2-3 simple sections (features grid, stats, CTA) custom. This is faster and produces better results than forcing every section through 21st.dev.

Phase 5: Installation & Integration

Install components:

npx shadcn@latest add "https://21st.dev/r/{author}/{component-name}"

What this does:

• Copies component source code to your project (usually components/ui/ or components/blocks/)
• Installs required npm dependencies
• Updates Tailwind config if needed
• Resolves internal component dependencies

Installation order matters:

1. Install base/primitive components first (buttons, inputs)
2. Then composite components that may depend on them (forms, dialogs)
3. Finally section-level components (hero, pricing)

Post-Install Compatibility Fixes (CRITICAL)

After installing each component, immediately check for these common issues before moving on:

1. render prop vs asChild conflict: Many newer 21st.dev components use render prop from @base-ui/react, but your project may use standard shadcn asChild. If you see TypeScript errors about render prop:

// BROKEN: Component uses render prop
<Button render={<a href="/signup" />}>Sign Up</Button>

// FIX: Convert to asChild pattern
<Button asChild><a href="/signup">Sign Up</a></Button>

Check Button, SheetTrigger, SelectTrigger in every installed component.

2. Container width mismatch: Components may assume different max-widths. After installing, verify each component uses a consistent container:

// If component uses its own container, it may conflict with your layout
// Wrap all sections in a consistent container OR
// Remove the component's internal container and use your own
<section className="py-20">
  <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">{/* component content here */}</div>
</section>

3. Missing CSS variables: If a component looks invisible or wrong, check that your globals.css defines all required CSS variables. Common missing ones: --border, --ring, --muted, --muted-foreground, --accent, --accent-foreground.

4. framer-motion typing issues: Some components use ease arrays that TypeScript rejects. Fix by casting:

// BROKEN
ease: [0.16, 1, 0.3, 1];
// FIX
ease: [0.16, 1, 0.3, 1] as const;

5. Faint/invisible card backgrounds: Many 21st.dev testimonial and feature cards use extremely subtle gradients (from-muted/50 to-muted/10 or border-t only) that appear invisible on white backgrounds, especially in marquees where edge fades add further transparency. Fix by giving cards visible styling:

// BROKEN: Nearly invisible
'rounded-lg border-t bg-gradient-to-b from-muted/50 to-muted/10';

// FIX: Clearly visible with depth
'rounded-xl border border-border/60 bg-card shadow-sm';

6. Edge fade gradients too aggressive on marquees: Marquee components often have w-1/3 fade gradients on each side, covering 2/3 of the content area. Reduce to w-1/6 so cards remain visible:

// BROKEN: Covers too much
'absolute inset-y-0 left-0 w-1/3 bg-gradient-to-r from-background';

// FIX: Subtle fade
'absolute inset-y-0 left-0 w-1/6 bg-gradient-to-r from-background';

7. Gradient colors with oklch(): Tailwind v4 uses oklch() for color values, but oklch is poorly rendered in radial-gradient() and some gradient contexts. Use rgba() or hex values for custom gradients:

// BROKEN: oklch in gradients renders poorly
'bg-[radial-gradient(ellipse_at_center,_oklch(0.55_0.28_285_/_0.18)_0%,_transparent_65%)]';

// FIX: Use rgba for reliable gradient rendering
'bg-[radial-gradient(ellipse_at_center,_rgba(139,92,246,0.18)_0%,_transparent_65%)]';

8. Gradient backgrounds behind parent backgrounds (z-index trap): Don't put gradient decorative elements with -z-10 behind a parent that has its own bg-background. The parent's opaque background covers the gradient. Instead, apply the gradient directly on the section:

// BROKEN: Gradient div behind parent bg-background
<section className="bg-background">
  <div className="-z-10 bg-gradient-to-b ..."> {/* invisible! */}

// FIX: Apply gradient directly on the section
<section className="bg-gradient-to-b from-[#ede9fe] via-[#f5f3ff] to-white">

If installation fails:

1. Check error message — usually a missing peer dependency
2. Try npm install {missing-dep} then retry
3. If component URL is wrong, search 21st.dev for the correct path
4. Last resort: fetch the component code via WebFetch and create files manually

Phase 6: Page Composition

Layout Normalization (DO THIS FIRST)

Before composing, normalize the layout of all installed components so they play well together. 21st.dev components from different authors often have conflicting container widths, padding, and alignment. Fix this upfront:

1. Pick one container width for the entire page: max-w-7xl mx-auto px-4 sm:px-6 lg:px-8
2. Open each installed component file and check if it has its own container/max-width
3. Either: remove the component's internal container and wrap it externally, or ensure it matches your chosen width
4. Check text alignment: some components center-align content, others left-align. Normalize.
5. Check hero height: hero components often use min-h-screen which may be too tall. Adjust to min-h-[80vh] or less if needed.

Composition Patterns

Landing Page:

<Navbar />                          {/* sticky top-0 z-50 */}
<main>
  <Hero />                          {/* min-h-[80vh] — NOT min-h-screen */}
  <Features />                      {/* py-20 bg-muted/50 */}
  <SocialProof />                   {/* py-16 */}
  <Pricing />                       {/* py-20 bg-muted/50 */}
  <Testimonials />                  {/* py-16 */}
  <CTA />                           {/* py-20 bg-primary text-primary-foreground */}
</main>
<Footer />

Dashboard:

<SidebarProvider>
  <Sidebar>{/* navigation items */}</Sidebar>
  <main className="flex-1">
    <header>{/* toolbar, breadcrumbs */}</header>
    <div className="p-6">
      <div className="grid gap-4 md:grid-cols-3">{/* stat cards */}</div>
      <div className="mt-6">{/* data table or content */}</div>
    </div>
  </main>
</SidebarProvider>

Auth Flow:

<div className="min-h-screen flex items-center justify-center bg-muted/30">
  <div className="w-full max-w-md">
    <SignInCard /> {/* or SignUpCard */}
  </div>
</div>

Multi-page App Layout:

// app/layout.tsx
<html>
  <body>
    <Navbar />
    {children}
    <Footer />
  </body>
</html>

Spacing & Layout Rules

• Sections: py-16 md:py-20 lg:py-24 (responsive vertical padding)
• Content width: max-w-7xl mx-auto px-4 sm:px-6 lg:px-8
• Card grids: grid gap-4 sm:grid-cols-2 lg:grid-cols-3
• Alternating section backgrounds: use bg-background and bg-muted/50

Dark Mode Setup

21st.dev components use CSS variables with dark: prefixes. Ensure:

// In layout.tsx or providers
import { ThemeProvider } from 'next-themes';

<ThemeProvider attribute="class" defaultTheme="system" enableSystem>
  {children}
</ThemeProvider>;

Install next-themes: npm install next-themes

Font Setup

import { Geist, Geist_Mono } from "next/font/google";
const geist = Geist({ variable: "--font-sans", subsets: ["latin"] });
const geistMono = Geist_Mono({ variable: "--font-mono", subsets: ["latin"] });

<body className={`${geist.variable} ${geistMono.variable} font-sans antialiased`}>

Phase 7: Customization & Refinement

After installing components, customize them to fit the project:

1. Content — Replace placeholder text, images, and links with real content
2. Colors — Choose brand color intentionally (see Color Selection below)
3. Typography — Ensure consistent font sizes and weights
4. Spacing — Align padding/margin with the rest of the page
5. Animations — Add or tune transitions using Tailwind or framer-motion
6. Responsiveness — Test at mobile, tablet, and desktop breakpoints

Color Selection (CRITICAL — Avoid AI Purple Bias)

AI models have a strong bias toward purple/violet as the default brand color. This is because purple dominates tech/AI branding (Figma, Notion AI, Copilot) and shadcn/ui examples. Using purple every time is an obvious AI fingerprint — like using the Sparkles icon.

Rule: NEVER default to purple. Choose colors based on the product type and industry:

Product / Industry	Recommended Primary	Avoid
Finance / Banking	Deep blue (oklch(0.45 0.15 250)), Navy, Teal	Purple, Neon
Health / Wellness	Green (oklch(0.55 0.18 155)), Teal, Soft blue	Red, Purple
E-commerce / Retail	Orange (oklch(0.65 0.2 50)), Coral, Amber	Muted grays
Developer tools	Emerald (oklch(0.55 0.17 160)), Cyan, Slate	Purple (overused)
Creative / Design	Rose (oklch(0.6 0.18 10)), Amber, Indigo	Plain blue
Education	Blue (oklch(0.5 0.16 250)), Teal, Green	Neon, Dark themes
Food / Restaurant	Warm red (oklch(0.55 0.22 25)), Orange, Olive	Cold blues
AI / Writing tools	Teal (oklch(0.55 0.12 195)), Blue-green, Slate	Purple (cliché!)
Enterprise / B2B	Slate blue (oklch(0.5 0.1 255)), Navy, Steel	Bright neons
Social / Community	Coral (oklch(0.6 0.17 25)), Sky blue, Warm pink	Dull grays

If the user specifies a brand color, use it. If not, pick from the table above — but NEVER purple unless the user explicitly asks for it.

How to apply the chosen color:

/* globals.css — example with teal for an AI writing tool */
:root {
  --brand: oklch(0.55 0.12 195); /* Teal, NOT purple */
}

Then use bg-brand, text-brand, border-brand/30 etc. throughout the site. Update hero gradients, CTA buttons, icon backgrounds, and accent colors to match.

Hero Visual Quality Checklist

Hero sections make or break the first impression. After installing a hero component, ensure:

• Heading contrast: On colored/gradient backgrounds, use solid text-foreground instead of gradient-text effects (bg-clip-text text-transparent) which can be too faint
• Background gradients: Apply gradients directly on the section element (bg-gradient-to-b from-[color] via-[color] to-white) — don't layer decorative gradient divs behind opaque parents
• Product mockups: For SaaS sites, build a realistic inline mockup (editor, dashboard, chat) instead of using a placehold.co image. Include window chrome (red/yellow/green dots), sidebar, content area, and status indicators. This dramatically improves perceived quality.
• CTA styling: Use rounded-xl, visible shadows (shadow-lg), and brand colors. Add hover effects (hover:-translate-y-0.5 transition-transform)
• Radial glow accents: Add subtle radial gradients using rgba() colors (not oklch) for depth behind hero content
• Avoid AI-cliché icons: NEVER use Sparkles/Stars/Wand icons — they instantly signal "AI-generated." Use minimal alternatives: a pulsing dot indicator, a small "NEW" badge, or just well-styled text. The goal is to look like a senior human designer made it, not an AI.
• Avoid AI-cliché colors: NEVER default to purple/violet. Choose colors from the Color Selection table based on the product type. Purple is the #1 AI color bias.

CSS Variable Theming

/* globals.css */
@layer base {
  :root {
    --background: 0 0% 100%;
    --foreground: 0 0% 3.9%;
    --primary: 0 0% 9%;
    --primary-foreground: 0 0% 98%;
    /* ... customize these to match brand */
  }
  .dark {
    --background: 0 0% 3.9%;
    --foreground: 0 0% 98%;
    /* ... dark variants */
  }
}

Phase 8: Verification (THOROUGH)

This phase catches the bugs that ruin the user's first impression. Do not skip any step.

Step 1: Build passes

npm run build

Fix any TypeScript or build errors before proceeding.

Step 2: Visual inspection (MOST IMPORTANT)

Run npm run dev and actually look at every section of the page:

1. Take a screenshot or use preview_screenshot — look at the full page from top to bottom

2. Check for these common problems:

   • Blank/white sections — content exists in DOM but invisible? Check CSS variables, text color matches background
   • Content overflow — text or elements going off-screen to the right? Check container width, remove text-center or adjust max-w
   • Giant blank spaces — hero taking up too much vertical space? Reduce min-h-screen to min-h-[80vh]
   • Misaligned sections — some sections centered, others left-aligned? Normalize container classes
   • Broken images — placeholder URLs not loading? Replace with real images or remove

3. Scroll through the entire page — every section must be visible and properly styled

Step 3: Responsiveness

Test at 3 breakpoints using preview_resize or browser devtools:

• Mobile (375px): single column, readable text, no horizontal overflow
• Tablet (768px): proper grid transition
• Desktop (1280px): full layout as designed

Step 4: Interactions

• Click every button and link
• Test navbar dropdown/mobile menu
• Test any toggles or tabs

Step 5: Console check

No errors in browser console. Warnings about missing images or unused vars are acceptable.

If any visual issue is found in Steps 2-3, fix it immediately before presenting to the user. The most common fixes are: adjusting container width, fixing CSS variable colors, and reducing hero height.

Advanced Patterns

Component Dependency Chain

Some 21st.dev components depend on other components. The npx installer handles this automatically, but be aware:

• A Dialog component may install Button as a dependency
• If you've already customized Button, the dialog install might overwrite it
• Install from leaf components up, and keep track of what's been customized

Mixing Authors Safely

When combining components from different authors:

1. Check that all use the same CSS variable naming (most shadcn-based ones do)
2. Normalize border-radius: pick one style and apply globally via CSS variables
3. Ensure animation timing is consistent (ease-in-out, duration-200)
4. Watch for conflicting Tailwind config extensions

Building Component Variations

If 21st.dev doesn't have exactly what you need:

1. Find the closest match
2. Install it
3. Modify the source code directly (you own it!)
4. The component file is in your project — edit freely

Updating Component Knowledge

At the start of every build session, refresh your knowledge of available components by browsing the relevant category pages on 21st.dev. The platform adds new components daily, so what was the best option last week might be surpassed by something better today.

This means: if you last browsed https://21st.dev/s/hero an hour ago, browse it again if you're starting a new build. Fresh data leads to better component choices.

Error Recovery

Problem	Solution
Component not found	Try alternative spellings, browse the parent category, or search with WebSearch
npx install fails	Check for missing peer deps, verify URL format, try npm install for deps first
Component looks wrong	Check if Tailwind config was updated, verify CSS variables are defined
Dark mode broken	Ensure ThemeProvider wraps the app, check CSS variable definitions
TypeScript errors	Check component's expected props, install missing @types packages
Styling conflicts	Check for conflicting Tailwind classes, CSS variable naming collisions
21st.dev unreachable	Use WebSearch to find component names, construct install URLs from cached knowledge
Component too complex	Simplify by removing unused features from the source code
render prop errors	Component uses @base-ui/react pattern — convert to asChild pattern
Giant blank space	Hero/section using min-h-screen — reduce to min-h-[80vh] or remove
Content off-screen right	Container width mismatch — add max-w-7xl mx-auto wrapper
Invisible text	CSS variables undefined — check globals.css has all required color tokens
Faint/invisible cards	Background gradient too subtle — use bg-card border border-border/60 shadow-sm
Marquee cards hidden	Edge fade w-1/3 too wide — reduce to w-1/6
Gradient not showing	Using -z-10 behind parent bg-background — apply gradient directly on section
oklch gradient broken	oklch renders poorly in radial-gradient() — use rgba() hex values instead
Heading invisible on gradient	bg-clip-text text-transparent too faint — use solid text-foreground

MCP Setup (Optional)

For AI-powered component generation, set up the Magic MCP:

npx @21st-dev/cli@latest install claude --api-key <YOUR_API_KEY>

Get API key: https://21st.dev/settings/api-keys

Manual config in .claude/settings.json:

{
  "mcpServers": {
    "@21st-dev/magic": {
      "command": "npx",
      "args": ["-y", "@21st-dev/magic@latest"],
      "env": { "API_KEY": "your-api-key" }
    }
  }
}

MCP provides these tools:

• 21st_magic_component_builder — Generate components from descriptions
• 21st_magic_component_inspiration — Browse component ideas
• logo_search — Find company logos (via SVGL)