favicon

Favicon Generator Skill

Purpose: Generate a complete set of favicons from a source image and wire them into the project's HTML layout, web manifest, and assets directory.

Supported source formats: PNG, JPG, JPEG, SVG, WEBP, GIF

When to Use

• User asks to generate favicons or icons from an image
• New project setup needs favicon assets
• Replacing an outdated favicon set
• Adding PWA-compatible icons (web-app-manifest-*.png)

Prerequisites

ImageMagick v7+ required. Verify with:

which magick

If missing:

• macOS: brew install imagemagick
• Linux: sudo apt install imagemagick

Workflow

1. Validate Source Image

• Check source file exists
• Verify supported format (PNG, JPG, JPEG, SVG, WEBP, GIF)
• Note if SVG (gets special handling — direct copy + <link rel="icon" type="image/svg+xml">)

If invalid, report error and stop.

2. Detect Framework

Check for marker files to identify framework and assets directory:

Framework	Marker File	Assets Directory
Rails	config/routes.rb	public/
Next.js	next.config.*	public/
Gatsby	gatsby-config.*	static/
SvelteKit	svelte.config.*	static/
Astro	astro.config.*	public/
Hugo	hugo.toml or hugo.yaml	static/
Jekyll	_config.yml	Root directory
Vite	vite.config.*	public/
Create React App	package.json with react-scripts	public/
Vue CLI	vue.config.*	public/
Angular	angular.json	src/assets/
Eleventy	.eleventy.js or eleventy.config.*	Root or _site/
Static HTML	index.html in root	Same directory as HTML

Priority rule: If existing favicon files found (favicon.ico, apple-touch-icon.png), use their location regardless of framework detection.

If uncertain about asset placement → use AskUserQuestion to confirm target directory.

3. Resolve App Name

Check sources in order (use first found):

1. Existing site.webmanifest → name field
2. package.json → name field
3. Rails config/application.rb → module name
4. Current directory name

Convert to title case for display.

4. Generate Favicon Assets

Run ImageMagick commands (preserve alpha with -alpha on -background none):

# Multi-resolution ICO (16x16, 32x32, 48x48)
magick "<source>" -alpha on -background none \
  \( -clone 0 -resize 16x16 \) \
  \( -clone 0 -resize 32x32 \) \
  \( -clone 0 -resize 48x48 \) \
  -delete 0 "<target>/favicon.ico"

# PNG variants
magick "<source>" -alpha on -background none -resize 96x96 "<target>/favicon-96x96.png"
magick "<source>" -alpha on -background none -resize 180x180 "<target>/apple-touch-icon.png"
magick "<source>" -alpha on -background none -resize 192x192 "<target>/web-app-manifest-192x192.png"
magick "<source>" -alpha on -background none -resize 512x512 "<target>/web-app-manifest-512x512.png"

If source is SVG, also copy directly:

cp "<source>" "<target>/favicon.svg"

5. Generate or Update Web Manifest

Create or update site.webmanifest in target directory.

If exists: preserve theme_color, background_color, display values.

{
  "name": "<app-name>",
  "short_name": "<app-name>",
  "icons": [
    { "src": "/web-app-manifest-192x192.png", "sizes": "192x192", "type": "image/png", "purpose": "maskable" },
    { "src": "/web-app-manifest-512x512.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable" }
  ],
  "theme_color": "#ffffff",
  "background_color": "#ffffff",
  "display": "standalone"
}

6. Update HTML Layout

Rails → Edit app/views/layouts/application.html.erb:

<link rel="icon" type="image/png" href="/favicon-96x96.png" sizes="96x96" />
<link rel="icon" type="image/svg+xml" href="/favicon.svg" />
<link rel="shortcut icon" href="/favicon.ico" />
<link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png" />
<meta name="apple-mobile-web-app-title" content="<app-name>" />
<link rel="manifest" href="/site.webmanifest" />

Next.js → Edit app/layout.tsx or app/layout.js metadata export:

export const metadata = {
  // ... existing metadata
  icons: {
    icon: [
      { url: '/favicon.ico', sizes: '48x48' },
      { url: '/favicon-96x96.png', sizes: '96x96', type: 'image/png' },
      { url: '/favicon.svg', type: 'image/svg+xml' },
    ],
    apple: [
      { url: '/apple-touch-icon.png', sizes: '180x180' },
    ],
  },
  manifest: '/site.webmanifest',
  appleWebApp: {
    title: '<app-name>',
  },
}

Static HTML → Edit index.html <head>:

<link rel="icon" type="image/png" href="/favicon-96x96.png" sizes="96x96" />
<link rel="icon" type="image/svg+xml" href="/favicon.svg" />
<link rel="shortcut icon" href="/favicon.ico" />
<link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png" />
<meta name="apple-mobile-web-app-title" content="<app-name>" />
<link rel="manifest" href="/site.webmanifest" />

Other/Unknown → Output HTML snippet for user to add manually.

Note: Omit SVG-related tags if source was not SVG format.

7. Report Summary

## Favicon Generation Complete

- **Framework:** <detected-framework>
- **Assets directory:** <target-path>
- **App name:** <resolved-name>

### Generated Files
- favicon.ico (16x16, 32x32, 48x48)
- favicon-96x96.png
- apple-touch-icon.png (180x180)
- web-app-manifest-192x192.png
- web-app-manifest-512x512.png
- site.webmanifest
[- favicon.svg (if source was SVG)]

### Updated Files
- <layout-file-path>

### Overwrites
[List any existing files that were replaced]