PrinterFlo Image Optimizer

How this differs from every other image optimizer: the other plugins in this category compress on a remote server (metered credits) or with your host’s ImageMagick/GD (no AVIF on shared hosting). PrinterFlo Image Optimizer is, to our knowledge, the only one that runs the actual encoders (libwebp, libavif) as WebAssembly in the site owner’s browser — which is why it can be unlimited and free, needs no API key, sends no images anywhere, and can produce AVIF on any hosting plan.

Every image optimizer plugin has the same catch: your images get sent to their servers, servers cost money, so you get metered — 100 images/month, 20 MB/month, « upgrade for bulk. »

This plugin has no server. It converts your media library to WebP (and optionally AVIF) using WebAssembly running in your own browser — the same open-source encoders (Google’s libwebp and libavif) that power professional optimization services, just running on your machine instead of theirs.

• Truly unlimited — 50 images or 50,000. There is nothing to meter.
• No account, no API key, no signup — install, click Optimize, done.
• AVIF on any hosting — shared hosts usually can’t encode AVIF server-side. Your browser can. Get the most modern format on the cheapest hosting.
• Zero server load — your host does no conversion work at all.
• Private — images never leave your site. Nothing is sent to any third party.
• Originals untouched — converted files are saved alongside your originals; one click removes them all.
• Automatic delivery — front-end images are wrapped in <picture> tags so every visitor’s browser picks the best format it supports. Works on any host — no .htaccess or nginx changes.

How it works

Open Media → Image Optimizer and click Optimize all images. Your browser fetches each image (and every thumbnail size), converts it with WebAssembly, and saves the result back to your media library. Keep the tab open while it runs — that’s the whole trick that makes unlimited possible.

The one honest trade-off: because conversion happens in a browser, new uploads aren’t converted automatically in the background. Revisit the page after adding images and run it again — already-converted files are skipped, so it only processes what’s new.

Built by PrinterFlo, print shop management software. Try the same engine online: free bulk WebP & AVIF converter.

External services

None. This plugin makes no requests to any external service. All image processing happens locally in the site administrator’s browser using bundled WebAssembly encoders (libwebp and libavif via jSquash, Apache-2.0 licensed).

Source code

The JavaScript in assets/dist/ is built from the unminified sources in assets/src/ (Vite; see assets/src/vite.config.js). Both are included in this plugin. To rebuild: cd assets/src && npm install && npm run build.

About the .wasm files in assets/dist/: these WebAssembly binaries ARE the image encoders/decoders — they are essential to the plugin (it performs all conversion in the browser, so without them it does nothing). They are the unmodified, pre-built codec binaries shipped by the open-source jSquash project (Apache-2.0), pulled in verbatim from the @jsquash/webp and @jsquash/avif npm packages by the build above:

• webp_enc*.wasm / webp_dec*.wasm — Google’s libwebp encoder/decoder, compiled to WebAssembly with Emscripten (build source: jSquash codec directory).
• avif_enc*.wasm / avif_dec*.wasm — libavif + libaom encoder/decoder, same toolchain (build source: jSquash codec directory).

These codecs originate from the GoogleChromeLabs Squoosh project. Complete corresponding source and build instructions for every binary are at the links above.