redline-js

Design review, directly on your site.

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redline-js adds an inspection layer to any website — designers click any element to see its exact properties (font, color, spacing) and suggest edits. Changes are exported as structured JSON, ready for developer handoff.

No more back-and-forth. No more screenshots with arrows.

Features

• Figma-style typography panel — font, weight, size, line height, tracking, alignment, color
• Smart font detection — auto-detects loaded fonts from CSS custom properties and document.fonts
• Design system aware — optional token matching (colors, typography presets, font families)
• Tailwind inspector — classes grouped by category, responsive variants, CSS mappings
• Box model diagram — visual margin, border, padding, content
• Live editing — click any value to change it, changes apply instantly
• Persistent changes — localStorage with build hash invalidation
• JSON export — structured file ready for developer handoff
• Framework agnostic — vanilla JS core + React adapter
• Zero config — works out of the box, design system config is optional

Install

npm install redline-js

Quick Start

Vanilla JS

<script type="module">
  import { createDesignReview } from 'redline-js';

  createDesignReview({
    enabled: true,
    buildHash: 'my-build-123',
  });
</script>

React / Next.js

import { DesignReviewProvider } from 'redline-js/react';

export default function Layout({ children }) {
  return (
    <>
      {children}
      <DesignReviewProvider config={{
        enabled: process.env.NEXT_PUBLIC_DESIGN_REVIEW === 'true',
        buildHash: process.env.NEXT_PUBLIC_BUILD_HASH,
      }} />
    </>
  );
}

Then start with:

NEXT_PUBLIC_DESIGN_REVIEW=true npm run dev

How It Works

1. A red R button appears in the corner of the page
2. Click it to activate inspection mode
3. Hover over any element to see its box model overlay
4. Click to open the inspection panel:
   • Typography summary — Figma-style: font, weight (SemiBold not 600), size, line height, tracking as %, color with token name
   • Tailwind classes grouped by category (typography, colors, spacing, etc.)
   • Responsive variants (sm, md, lg) highlighted separately
   • CSS mappings — see what each Tailwind class resolves to
   • Box model diagram — margin, border, padding, content
5. Click any value to edit it live — changes apply instantly
6. Changes persist in localStorage across page refreshes
7. Export as JSON — structured file ready for developer handoff

Design System Integration

Optionally pass your design system tokens for richer inspection:

<DesignReviewProvider config={{
  enabled: true,
  designSystem: {
    fonts: [
      { family: 'Bricolage Grotesque', weights: [400, 500, 600, 700] },
      { family: 'Inter', weights: [400, 500, 600] },
    ],
    colors: {
      'green-500': '#0B493D',
      'mint-500': '#A1EDB1',
      'neutral-900': '#111111',
    },
    typography: [
      {
        name: 'Desktop/H1',
        fontFamily: 'Bricolage Grotesque',
        fontWeight: 600,
        fontSize: '64px',
        lineHeight: '72px',
        letterSpacing: '-4%',
      },
    ],
  },
}} />

When configured:

• Font select shows your design system fonts (otherwise auto-detected from the page)
• Weight select shows only weights available for the selected font
• Color shows the token name alongside the hex value (e.g., #0B493D green-500)
• Typography preset badge appears when values match a named style (e.g., Desktop/H1)

Build Hash

Prevents stale edits from being re-applied after code changes:

// next.config.ts
const nextConfig = {
  env: {
    NEXT_PUBLIC_BUILD_HASH: `${Date.now()}-${Math.random().toString(36).slice(2)}`,
  },
};

Designer makes edits, developer applies fixes, new build hash, old edits are automatically cleared.

Configuration

Option	Type	Default	Description
enabled	boolean	false	Show the widget
buildHash	string	'dev'	Change per deploy to invalidate saved edits
position	'top-left' | 'top-right' | 'bottom-left' | 'bottom-right'	'bottom-right'	Widget position
theme	'light' | 'dark'	'light'	Panel theme
panelWidth	number	360	Panel width in px
zIndex	number	999999	Widget z-index
storageKey	string	'__redline-changes__'	localStorage key
tailwindVersion	3 | 4 | 'auto'	'auto'	Tailwind version detection
exclude	string[]	[]	CSS selectors to skip
designSystem	DesignSystemConfig	—	Design system tokens (fonts, colors, typography presets)
onExport	(data) => void	—	Custom export handler

API

Vanilla JS

const rl = createDesignReview(config);

rl.activate();       // Start inspection mode
rl.deactivate();     // Stop inspection mode
rl.toggle();         // Toggle on/off
rl.isActive();       // Check state
rl.getChanges();     // Get tracked changes
rl.exportChanges();  // Get export payload
rl.clearChanges();   // Clear all + rollback
rl.destroy();        // Full cleanup

React Hook

import { useDesignReview } from 'redline-js/react';

function DesignToolbar() {
  const { isActive, toggle, changes, exportChanges, clearChanges } = useDesignReview();

  return (
    <button onClick={toggle}>
      {isActive ? 'Stop' : 'Inspect'} ({changes.length} changes)
    </button>
  );
}

Export Format

{
  "changes": [{
    "selector": "div > h2:nth-of-type(1)",
    "componentHint": "HeroTitle",
    "breakpoint": "base",
    "page": "/piattaforma",
    "modifications": [{
      "property": "font-size",
      "originalValue": "32px",
      "newValue": "28px"
    }],
    "timestamp": "2026-03-23T21:16:00Z"
  }],
  "metadata": {
    "exportedAt": "2026-03-23T21:20:00Z",
    "totalChanges": 1,
    "pages": ["/piattaforma"],
    "toolVersion": "0.1.0"
  }
}

Keyboard Shortcuts

Key	Action
Esc	Deselect element or deactivate
Click same element	Deselect

License

MIT