favicon

imagebrianlovin2.7K installs

Generate a complete set of favicons from a source image and update HTML. Use when setting up favicons for a web project.

Install

npx skills add https://github.com/brianlovin/agent-config --skill favicon

SKILL.md

---name: favicondescription: Generate a complete set of favicons from a source image and update HTML. Use when setting up favicons for a web project.argument-hint: [path to source image]---

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

Verify the source image exists at the provided path: $1
Check the file extension is a supported format (PNG, JPG, JPEG, SVG, WEBP, GIF)
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):

Existing site.webmanifest - Check the detected static assets directory for an existing manifest and extract the name field
package.json - Extract the name field if it exists
Rails config/application.rb - Extract the module name (e.g., module MyApp → "MyApp")
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.

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

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

favicon-96x96.png

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

apple-touch-icon.png (180x180)

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

web-app-manifest-192x192.png

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

web-app-manifest-512x512.png

magick "$1" -resize 512x512 -background none -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]',
  },
};