Why ImageOptim never added WebP, AVIF, or JPEG XL

ImageOptim has been the default Mac image optimizer for over a decade. It is free, open source, and good at what it does. But what it does has not changed since roughly 2014. JPEG, PNG, GIF, and SVG. No WebP. No AVIF. No JPEG XL. No HEIC.

This post looks at why the format gap exists and lists three concrete alternatives that ship the modern formats today.

A short history of what ImageOptim actually is

ImageOptim is a Mac frontend over a set of command-line image optimizers. jpegoptim, jpegtran, MozJPEG, pngcrush, OptiPNG, pngquant, gifsicle, and svgo all live inside the app bundle. When you drag a folder in, ImageOptim runs the appropriate tool for each file, compares the output, and keeps the smaller one if quality is preserved.

That is the whole architecture. It is elegant, it is fast, and it answers a real question: how do I shrink a JPEG or PNG without losing visible quality.

The architecture also explains why the format list stopped growing. New formats arrived from new ecosystems: WebP from Google’s libwebp, AVIF from the AV1 video codec, JPEG XL from libjxl. None of them ship as drop-in command-line tools that match the shape of pngcrush or jpegoptim. Adding them is not a matter of including another binary. It is a question of building a new pipeline around a completely different kind of encoder, one that often does not have a “keep the smaller of two outputs” mode at all.

What ImageOptim still does well

It is worth being clear about what the app still does and does well.

JPEG and PNG optimization is the bulk of image work on most websites that have not migrated to AVIF. ImageOptim runs the same lossless tools you would otherwise install with Homebrew, in a UI that takes no setup. For a developer who wants their build pipeline to shrink existing JPEGs and PNGs by 10 to 30 percent, it is the lowest-friction tool that exists.

It is also free. The source is on GitHub, the binary is on the project’s website, and the price tag is zero. Any criticism of what is missing has to account for that.

What is actually missing

Three formats matter and are not there.

WebP is the format Chrome has shipped since 2010 and Safari since 2020. By 2026 every browser supports it. For a site that ships images to a long tail of devices, WebP is the safe pick. ImageOptim users currently round-trip through other tools or skip WebP entirely.

AVIF is the smaller, modern successor. A photograph at quality 80 typically shrinks by 30 to 50 percent against the equivalent JPEG. All major browsers ship it. For new web projects in 2026, AVIF is the format you would default to. ImageOptim has no path to it.

JPEG XL is the archival format. Its trick is lossless transcoding of an existing JPEG into a smaller JXL file that can be decoded back into the original byte-identical JPEG. Safari and iOS 17 support it. Chrome and Firefox have not enabled it by default. For storing photo libraries this is the most interesting format of the three, and ImageOptim has no path to it either.

There is also no HEIC encoder, which matters less for web work but a lot for anyone shipping Apple-native workflows.

Three alternatives that ship the modern formats

Squash 3 from Realmac Software. Ships on the Mac App Store, supports WebP, AVIF, and HEIC. The pricing model moved to subscription in recent versions, which some long-time users dislike, but the encoder list is broad. JPEG XL is not yet included as of 2026.

Zipic from Okooo Studio. Direct download only, one-time purchase, supports a dozen formats including JPEG XL. The trade-off is that it lives outside the App Store, so updates, sandboxing, and trust are on you to verify, and there is no Mac App Store rating signal to lean on before buying.

Sqz is the one I work on. It ships on the Mac App Store at a one-time price, supports JPEG XL with the lossless transcoding mode described above, plus AVIF, WebP, HEIC, jpegli for JPEG, and pngquant for PNG. The reason it exists is that no other App Store app combines those formats with a one-time license.

There are other tools. Squoosh runs in a browser and is excellent for a single image at a time. Compresso supports broad formats but skips JXL. XL Converter is the best JXL tool overall but ships only for Windows and Linux. On the Mac App Store specifically, the list of options that ship every modern format is short.

When ImageOptim still wins

For two cases it is still the right answer.

If you already have a build pipeline of JPEGs and PNGs and you want lossless optimization of those formats with no configuration, ImageOptim is the fastest path from “drag folder” to “smaller files.” Modern format encoders have a learning curve that ImageOptim’s command-line ancestors do not.

If your audience explicitly does not have modern browsers and you cannot ship AVIF or WebP, the format gap stops mattering. You still want jpegoptim and pngquant.

For anything else in 2026, the alternatives are worth a look. The modern formats are not marginal anymore. They are the default.