Crunch is a free, open-source Mac utility that shrinks PNG files to a fraction of their original size using a two-pass lossy-then-lossless compression pipeline.
What is Crunch?
Crunch is a PNG image compressor for macOS that chains a lossy quantisation stage (via pngquant) with a lossless deflate optimisation stage (via zopfli) to squeeze every spare byte out of a PNG without requiring you to touch a command line. Unlike a simple "save for web" export from Photoshop or Preview, Crunch deliberately trades a small amount of invisible colour precision for dramatic file-size reductions — regularly cutting files to under a third of their starting weight.
The project lives on GitHub under Chris Simpkins's account and is actively maintained. Because it is open source, you can inspect exactly what it does to your pixels before trusting it with production assets.
What does Crunch do best?
Crunch excels at bulk-optimising screenshots, UI assets, and web graphics where PNG transparency is non-negotiable but file weight still matters. Drop a folder of retina-resolution interface screenshots onto it and you will routinely see savings in the 50–70% range — savings that tools like ImageOptim's lossless-only mode simply cannot match.
The native macOS drag-and-drop interface means the workflow is genuinely fast: drag PNGs onto the window, watch the progress bars, collect the optimised copies in the same folder (Crunch appends -crunch to the filename so your originals are never overwritten). There is no subscription, no cloud upload, no telemetry. Everything happens on-device.
- Two-stage compression: pngquant reduces colour depth first; zopfli then re-encodes the deflate stream for maximum density.
- Non-destructive output: originals are preserved; compressed copies carry a -crunch suffix.
- Batch-ready: handles dozens of files in one drop with per-file progress indicators.
- Completely offline: no pixels leave your machine.
Is Crunch free?
Yes — Crunch is entirely free to download and use. It is released under the MIT licence on GitHub, which means you can also inspect the source, fork it, or integrate its CLI into your own build pipeline at no cost. There is no pro tier, no feature gate, and no in-app purchase.
Who should use Crunch?
Crunch is ideal for front-end developers, macOS app developers, and content creators who publish PNG-heavy work to the web and want a no-friction way to cut page weight. If you already reach for ImageOptim on a daily basis, Crunch is worth keeping alongside it for situations where you want maximum compression and can accept the mild lossy quantisation step.
It is less suited to photographers or print professionals who need lossless-only pipelines, or anyone working primarily with JPEG, WebP, or AVIF. For those formats, tools like Squash or the Finder-integrated Permute are better fits. Similarly, if you need fine-grained quality sliders or side-by-side before/after previews, the more polished (and paid) ImageOptim Pro or Squash give you that interactive control that Crunch's utilitarian interface deliberately skips.
How does Crunch compare to ImageOptim?
ImageOptim is the friendlier, more feature-rich tool — it handles PNG, JPEG, and GIF in one window, integrates tightly with macOS Quick Look, and offers lossless-only mode as the default to protect sensitive assets. Crunch, by contrast, is PNG-only and always applies lossy quantisation. In my testing on retina screenshots, Crunch consistently delivered smaller output files than ImageOptim's default lossless pass, sometimes by a factor of two. The trade-off is that Crunch's colour reduction is visible under a loupe on gradients, whereas ImageOptim's lossless output is pixel-perfect.
Think of them as complementary rather than competing: ImageOptim for assets where fidelity is paramount, Crunch for bulk web exports where byte count is the primary concern.
What are the best Crunch alternatives?
For PNG compression on the Mac, the main alternatives are ImageOptim (free, lossless-first, multi-format), Squash (paid, polished UI, WebP/AVIF export), and the pngquant CLI directly (the same engine Crunch wraps, but terminal-only). If you prefer a subscription tool with cloud processing and broader format support, Compressor.io or TinyPNG's desktop app cover similar ground. For video and image batch work in one interface, Permute 3 is worth a look, though PNG compression is not its primary strength.
