mage

mage is a purpose-built, macOS command-line tool for the two things I do with most screenshots and images: resize them and convert them to WebP.

mage at work

For years, one of my everyday tools on macOS was OptImage. It handily resized images, converted them from one format to another, and optimized their file size. Simple and fast. But it broke when I upgraded to macOS 27.

There’s no indication it’s going to be upgraded or fixed, so I started looking for alternatives. My (narrow) requirements: (1) resize images (like large images and screenshots) by either percentage or max width and (2) convert images to WebP so they’re optimized for the web. ImageOptim predates WebP, and hasn’t added support. Clop is a nice, modern alternative, but it’s positioned as a power tool; it does way too much for my needs. And most other options were subscription-based.

Summoning mage 🧙

Finding no alternative that fit my requirements, I created mage as an interactive CLI tool. Why the command-line? Ghostty, a terminal replacement for macOS, is another one of my everyday apps. It’s always open, so it’s faster to jump there vs working with yet another app.

Here’s how it works:

• Type mage filename.png or, for batch processing: mage *.png (* selects any file that ends with .png). It also handles jpg, gif, and tiff files.
• Resize by percentage or max-width (or skip resizing)
• Convert to WebP, lossless or lossy (or skip converting). I’ve found using lossy set to 80 or 90 nets substantially smaller files with almost no perceived loss in quality, especially for images that end up on the web.
• Done. The original images stay in place.

Processing multiple images

For a concrete example: I took a screenshot that’s 2940×1912 and 1.6 MB. Resizing it by 50% and converting it to WebP using lossy 90 reduces the file size to 153 KB, or just over 90% smaller.

I built mage with Claude Code. I kicked off the project with the Superpowers plugin, which drives a spec-plan-build process. Once the plan was complete, the build finished in an afternoon.

Behind the scenes, mage uses tools I already had installed through Homebrew: ImageMagick and webp. They’re both wrapped with gum, a colorful, interactive command-line tool that makes the CLI feel friendlier.

Day-to-day, mage has fully replaced OptImage in my workflow. The interactive prompts mean I can quickly navigate options with the keyboard. And because OptImage required changing a preference to manage resizing, the mage-based workflow is actually faster.

If you want to give it a try, it’s free to use. You can find the installation steps here. It requires macOS, Homebrew, and the ImageMagick, webp, and gum Homebrew packages.

Tools used

• Claude Code (Pro) + Superpowers for specs and planning (free)
• ImageMagick, webp, and gum (free)
• Ghostty (or Terminal) (free)