icon-generator

name	icon-generator
description	Generate raster icon assets (PNG) from a single SVG source using the `resvg` CLI. Use whenever the user needs application icons, app/extension assets, favicons, or any multi-size PNG export from an SVG — for Chrome / browser extensions (16/48/128 px for manifest.json), PWA / web app manifests, macOS / Windows / Linux app bundles, favicons (16/32/180/192/512 px), README badges, or any "I need a PNG at size N" task. Trigger on phrases like "create icons", "generate icons", "app icon", "extension icon", "favicon", "アイコン画像を作って", "SVGからPNGを生成", or when a project's manifest references icon files that don't yet exist. Prefer this skill over hand-drawing in Canvas, using browser screenshots, or pulling in heavy Node tooling like `sharp` — it produces clean, deterministic, hash-stable output and leaves no build-time dependencies in the project.
license	MIT

Icon Generator

Generate crisp, deterministic PNG icons from a single SVG master, using the resvg CLI (a Rust-based renderer based on tiny-skia / usvg). The advantage over hand-rolling a Node script with sharp is that resvg is a single static binary, runs in well under a second per size, and renders SVGs with predictable text/shape handling. Because it's a one-shot CLI invocation, no build dependency is added to the project — only the generated PNGs are committed.

When to use this skill

• The user asks to create app, extension, or web icons in multiple sizes
• A manifest.json (Chrome extension, PWA, web app) references icon files that don't exist yet
• The user provides an SVG and asks for PNG exports at specific sizes
• The user wants favicons or social-share images derived from an SVG logo

Required tool: resvg

Check first:

which resvg && resvg --version

If missing, install via Cargo (the user must have cargo from a Rust toolchain). Confirm with the user before installing global tools:

cargo install resvg

This places the binary at ~/.cargo/bin/resvg. Compilation takes ~15–30 seconds on a modern Mac.

Standard sizes

Choose the size set that matches the target platform. If the user doesn't specify, default to the Chrome extension triple (16/48/128) when the project is a browser extension, otherwise ask.

Target	Sizes (px)
Chrome / Edge extension (MV3)	16, 48, 128
Firefox extension (WebExtension)	48, 96
PWA / web app manifest	192, 512 (often add 144, 384)
Favicon (basic)	16, 32
Favicon (apple-touch / Android)	180, 192, 512
macOS app icon (.icns base)	16, 32, 64, 128, 256, 512, 1024
Windows app icon (.ico base)	16, 32, 48, 256
GitHub social preview	1280 × 640 (single, not square)

Bundling PNGs into .icns (macOS) or .ico (Windows)

resvg only emits PNGs. To ship a real macOS / Windows app icon you need one more step.

macOS .icns uses Apple's iconutil (ships with Xcode Command Line Tools). The input is a directory named *.iconset/ containing PNGs with this exact naming — note that @2x means double the physical pixels of the base name:

Filename	Physical px
icon_16x16.png	16
[e-mail]	32
icon_32x32.png	32
[e-mail]	64
icon_128x128.png	128
[e-mail]	256
icon_256x256.png	256
[e-mail]	512
icon_512x512.png	512
[e-mail]	1024

Generate the 7 physical sizes with resvg, then cp the duplicates (icon_32x32.png and [e-mail] are bit-identical), then run iconutil -c icns AppIcon.iconset -o AppIcon.icns.

Windows .ico is a multi-resolution container. Generate the four PNGs with resvg, then bundle with ImageMagick: magick icon-16.png icon-32.png icon-48.png icon-256.png icon.ico. (If magick isn't available, brew install imagemagick.) .ico is itself a one-shot artifact, so don't add ImageMagick as a project dependency either.

Workflow

1. Decide on a layout for the SVG

The SVG should use viewBox="0 0 N N" (square, e.g. 0 0 128 128) so it scales cleanly to any size. Avoid:

• Stroke widths under 1 unit at 128-viewBox — they vanish at 16 px
• Text that relies on system fonts being installed (resvg can use a font dir, but it's simpler to convert text to paths)
• External assets (<image href="...">, external CSS); embed everything inline

For a square icon viewBox, design the focal element to occupy roughly the central 70% so it survives platform rounding/masking (especially on iOS/Android maskable icons).

Non-square targets (GitHub social preview 1280×640, OG images, banners): match the SVG's viewBox to the target aspect ratio, e.g. viewBox="0 0 1280 640". resvg --width N infers height from the viewBox, so a square SVG passed through --width 1280 outputs 1280×1280, not 1280×640. If you want to reuse a square logo inside a wider canvas, write a wrapper SVG with the target viewBox and embed the logo inline (<g transform="translate(... ) scale(...)">…logo children…</g>); do not use <image href="..."> or external <use> since those break inlining.

2. Place the source SVG

Put the source SVG somewhere the project keeps assets. For Chrome extensions with Vite/webpack, public/icons/icon.svg is conventional (the bundler copies public/ verbatim into the build output). If the project has no asset convention, ask.

3. Generate PNGs

Invoke resvg once per target size. The --width N flag also sets the height for square SVGs:

resvg --width 16  public/icons/icon.svg public/icons/icon-16.png
resvg --width 48  public/icons/icon.svg public/icons/icon-48.png
resvg --width 128 public/icons/icon.svg public/icons/icon-128.png

Verify the output:

file public/icons/icon-*.png
# Expect: PNG image data, NxN, 8-bit/color RGBA, non-interlaced

Use the Read tool on the largest PNG to visually confirm the design renders as intended before committing.

4. Wire into the project

For a Chrome extension manifest (Manifest V3):

{
  "icons": {
    "16":  "icons/icon-16.png",
    "48":  "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "action": {
    "default_icon": {
      "16":  "icons/icon-16.png",
      "48":  "icons/icon-48.png",
      "128": "icons/icon-128.png"
    }
  }
}

icons is the extension's own icon (Extensions page, install dialog). action.default_icon is what shows in the toolbar. They can point to the same files.

For a PWA manifest:

{
  "icons": [
    { "src": "icons/icon-192.png", "sizes": "192x192", "type": "image/png" },
    { "src": "icons/icon-512.png", "sizes": "512x512", "type": "image/png" },
    { "src": "icons/icon-512-maskable.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable" }
  ]
}

For HTML favicons:

<link rel="icon" type="image/png" sizes="16x16" href="/icons/icon-16.png">
<link rel="icon" type="image/png" sizes="32x32" href="/icons/icon-32.png">
<link rel="apple-touch-icon" sizes="180x180" href="/icons/icon-180.png">

5. Decide what to commit

Always commit:

• The source SVG (icon.svg) — it's the master file; regenerate from it whenever sizes change
• The generated PNGs — they're the actual shipped assets

Usually exclude from the bundled output (dist/, build/):

• The source SVG, if it's not referenced at runtime. With Vite, public/icons/icon.svg gets copied to dist/icons/icon.svg by default — add a postbuild step to delete it if you don't want it shipped.

Do NOT add resvg to the project's package.json — it's a one-shot generator, not a runtime or build dependency.

Common pitfalls

• resvg --width 16 --height 16: redundant for square SVGs and may cause confusion. Pass --width N only; resvg infers height from the SVG's aspect ratio.
• Tiny icons look muddy: at 16 px many designs degrade. Consider a simplified mark for ≤32 px (more whitespace, thicker strokes) and a richer mark for ≥48 px. If both are needed, keep two SVG sources (icon-small.svg, icon.svg) rather than fighting one source through all sizes.
• Maskable icons (PWA/Android): the OS may clip a circle / squircle out of the icon. Keep critical content inside a 40% safe zone centered in the canvas. Generate a separate *-maskable.png with this padding rather than reusing the regular icon.
• resvg can't render <foreignObject> (HTML inside SVG). Avoid it.
• Cargo install fails: confirm the user has Rust installed (rustup --version). If not, the alternative is brew install librsvg then rsvg-convert -w 16 -h 16 -f png icon.svg -o icon-16.png — same idea, different binary.

Example: Chrome extension icon (the canonical case)

A minimal "pen + sparkle" mark, blue background with rounded corners, white pen diagonally placed, yellow sparkles. Designed at viewBox 128 so the same SVG renders cleanly at 16/48/128:

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 128 128" width="128" height="128">
  <rect x="0" y="0" width="128" height="128" rx="24" ry="24" fill="#1a73e8"/>
  <g transform="translate(64 64) rotate(-45) translate(-64 -64)">
    <rect x="58" y="30" width="12" height="60" fill="#ffffff"/>
    <polygon points="58,90 70,90 64,108" fill="#ffffff"/>
  </g>
  <g transform="translate(94 34)" fill="#fbbc04">
    <path d="M0 -16 L4 -4 L16 0 L4 4 L0 16 L-4 4 L-16 0 L-4 -4 Z"/>
  </>

Generate:

resvg --width 16  icon.svg icon-16.png
resvg --width 48  icon.svg icon-48.png
resvg --width 128 icon.svg icon-128.png

Done. Three PNGs, no project dependencies added, source SVG kept for future tweaks.