favicon

name	favicon
argument-hint	["path to source image"]
description	Generate favicons from a source image
allowed-tools	Bash(magick *), Bash(which *), Bash(cp *), Bash(mkdir *)
metadata	{"author":"Steve Clarke","original-author":"Shpigford","version":"1.0"}

Generate a complete set of favicons from the source image at $1 and update the project's HTML with the appropriate link tags.

Prerequisites

First, verify ImageMagick v7+ is installed by running:

which magick

If not found, stop and instruct the user to install it:

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

Step 1: Validate Source Image

1. Verify the source image exists at the provided path: $1
2. Check the file extension is a supported format (PNG, JPG, JPEG, SVG, WEBP, GIF)
3. If the file doesn't exist or isn't a valid image format, report the error and stop

Note whether the source is an SVG file - if so, it will also be copied as favicon.svg.

Step 2: Detect Project Type and Static Assets Directory

Detect the project type and determine where static assets should be placed. Check in this order:

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

Important: If existing favicon files are found (e.g., favicon.ico, apple-touch-icon.png), use their location as the target directory regardless of framework detection.

Report the detected project type and the static assets directory that will be used.

When in doubt, ask: If you are not 100% confident about where static assets should be placed (e.g., ambiguous project structure, multiple potential locations, unfamiliar framework), use AskUserQuestionTool to confirm the target directory before proceeding. It's better to ask than to put files in the wrong place.

Step 3: Determine App Name

Find the app name from these sources (in priority order):

1. Existing site.webmanifest - Check the detected static assets directory for an existing manifest and extract the name field
2. package.json - Extract the name field if it exists
3. Rails config/application.rb - Extract the module name (e.g., module MyApp → "MyApp")
4. Directory name - Use the current working directory name as fallback

Convert the name to title case if needed (e.g., "my-app" → "My App").

Step 4: Ensure Static Assets Directory Exists

Check if the detected static assets directory exists. If not, create it.

Step 5: Generate Favicon Files

Run these ImageMagick commands to generate all favicon files. Replace [STATIC_DIR] with the detected static assets directory from Step 2.

Important: The -background none flag must come BEFORE the input file to properly preserve transparency when rendering SVGs. Placing it after the input will result in a white background.

favicon.ico (multi-resolution: 16x16, 32x32, 48x48)

magick -background none "$1" \
  \( -clone 0 -resize 16x16 \) \
  \( -clone 0 -resize 32x32 \) \
  \( -clone 0 -resize 48x48 \) \
  -delete 0 -alpha on \
  [STATIC_DIR]/favicon.ico

favicon-96x96.png

magick -background none "$1" -resize 96x96 -alpha on [STATIC_DIR]/favicon-96x96.png

apple-touch-icon.png (180x180)

magick -background none "$1" -resize 180x180 -alpha on [STATIC_DIR]/apple-touch-icon.png

web-app-manifest-192x192.png

magick -background none "$1" -resize 192x192 -alpha on [STATIC_DIR]/web-app-manifest-192x192.png

web-app-manifest-512x512.png

magick -background none "$1" -resize 512x512 -alpha on [STATIC_DIR]/web-app-manifest-512x512.png

favicon.svg (only if source is SVG)

If the source file has a .svg extension, copy it:

cp "$1" [STATIC_DIR]/favicon.svg

Step 6: Create/Update site.webmanifest

Create or update [STATIC_DIR]/site.webmanifest with this content (substitute the detected app name):

{
  "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"
}

If site.webmanifest already exists in the static directory, preserve the existing theme_color, background_color, and display values while updating the name, short_name, and icons array.

Step 7: Update HTML/Layout Files

Based on the detected project type, update the appropriate file. Adjust the href paths based on where the static assets directory is relative to the web root:

• If static files are in public/ or static/ and served from root → use /favicon.ico
• If static files are in src/assets/ → use /assets/favicon.ico
• If static files are in the same directory as HTML → use ./favicon.ico or just favicon.ico

For Rails Projects

Edit app/views/layouts/application.html.erb. Find the <head> section and add/replace favicon-related tags with:

<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" />

Important:

• If the source was NOT an SVG, omit the <link rel="icon" type="image/svg+xml" href="/favicon.svg" /> line
• Remove any existing <link rel="icon", <link rel="shortcut icon", <link rel="apple-touch-icon", or <link rel="manifest" tags before adding the new ones
• Place these tags near the top of the <head> section, after <meta charset> and <meta name="viewport"> if present

For Next.js Projects

Edit the detected layout file (app/layout.tsx or src/app/layout.tsx). Update or add the metadata export to include icons configuration:

export const metadata: Metadata = {
  // ... keep existing metadata fields
  icons: {
    icon: [
      { url: '/favicon.ico' },
      { url: '/favicon-96x96.png', sizes: '96x96', type: 'image/png' },
      { url: '/favicon.svg', type: 'image/svg+xml' },
    ],
    shortcut: '/favicon.ico',
    apple: '/apple-touch-icon.png',
  },
  manifest: '/site.webmanifest',
  appleWebApp: {
    title: '[APP_NAME]',
  },
};

Important:

• If the source was NOT an SVG, omit the { url: '/favicon.svg', type: 'image/svg+xml' } entry from the icon array
• If metadata export doesn't exist, create it with just the icons-related fields
• If metadata export exists, merge the icons configuration with existing fields

For Static HTML Projects

Edit the detected index.html file. Add the same HTML as Rails within the <head> section.

If No Project Detected

Skip HTML updates and inform the user they need to manually add the following to their 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" />

Step 8: Summary

Report completion with:

• Detected project type and framework
• Static assets directory used
• List of files generated
• App name used in manifest and HTML
• Layout file updated (or note if manual update is needed)
• Note if any existing files were overwritten

Error Handling

• If ImageMagick is not installed, provide installation instructions and stop
• If the source image doesn't exist, report the exact path that was tried and stop
• If ImageMagick commands fail, report the specific error message
• If the layout file cannot be found for HTML updates, generate files anyway and instruct on manual HTML addition