Apolo

Apolo is a free, open-source image optimizer for macOS, Windows and Linux. It compresses and converts images to WebP, AVIF, JPEG XL, JPEG and PNG on your own computer: nothing is uploaded anywhere.

Instead of guessing a quality number, you see what you lose before you save. You can compare with a slider, side by side or with a difference map, and every result shows its SSIMULACRA 2 score. You can also ask for a target such as "no visible loss", and Apolo finds the lowest quality that reaches it, photo by photo. In our tests on 24 Kodak photos, at the same perceived quality AVIF weighs 25% less than JPEG and JPEG XL up to 41% less.

Apolo uses the official engines: libwebp, MozJPEG, OxiPNG, libavif and libjxl. It produces the same file, byte for byte, as cwebp, cjpeg, oxipng, avifenc and cjxl, and every build checks this.

• Whole folders converted in parallel, to one or more formats at once. Apolo always writes new files and never overwrites your originals.
• Resize, crop and reduce the palette.
• Opens iPhone HEIC photos.
• A command line (apolo) that accepts the options of cwebp, cjpeg, oxipng, avifenc and cjxl.
• An MCP server, so Claude, Cursor and other AI agents can optimize images for you.

It runs natively on x64 and ARM, and installs from Homebrew, APT and RPM repositories or with a direct download. It is licensed under GPL-3.0 and made by Webcafeína.