favicon— agent skill

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

When to Use

• You need to generate a complete favicon set from a single source image.
• The task includes placing the assets in the correct framework-specific static directory and updating HTML link tags.
• You want one workflow that validates the source image, detects the project type, and writes the right favicon outputs.

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:

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