Image resize, compress & convert — offline

Photographs are the most personal files most people own, and image tools are the ones people reach for most casually. Resizing a photo of a passport for a visa form, compressing a screenshot that shows an internal dashboard, converting a picture of your children to attach to an email — all routinely uploaded to free converters whose business model is not always obvious.

Nothing is uploaded here. Decoding and encoding run in a Web Worker in your browser using WebAssembly builds of the same codecs Chrome uses, via jSquash. The site has no backend, and a Content-Security-Policy blocks third-party requests, so you can load the page, disconnect from the network, and still convert a batch of photos.

• AVIF — the smallest files by a clear margin, often half the size of a comparable JPEG. Supported by all current major browsers, though older software may not open it.
• WebP — nearly as small, with broader support across tools and platforms. The pragmatic default for the web today.
• JPG — universally supported by everything ever made. The safe choice for photographs going to an unknown recipient, an upload form, or a print shop.
• PNG — lossless, with transparency. Right for screenshots, logos, diagrams, and anything with text or sharp edges, where JPEG artefacts would show.

A practical rule: photographs to AVIF or WebP for the web and JPG for compatibility; graphics, screenshots, and anything containing text to PNG.

Browsers can encode images natively, but they do not agree on how. Native AVIF and WebP encoding varies significantly between engines — Safari especially — so the same picture at the same quality setting can come out at a noticeably different size and appearance depending on where it was converted.

Bundling the codecs means identical output everywhere, which is what you want when you are preparing assets that need to look the same for everyone. The browser's native encoder remains available as a fallback. The trade-off is a one-time download of the codec for the format you use — after which it is cached and the tool works offline.

iPhone photos are HEIC rather than JPEG, which is why they so often refuse to open on Windows and get rejected by upload forms. They are handled here directly, decoded on your device by a WebAssembly decoder that only loads when you actually drop a HEIC file. There is a walkthrough in converting HEIC to JPG.

Drop, paste, or pick multiple images and convert the whole set at once, downloading everything as a ZIP built on your device. The before-and-after comparison and the live file size readout update as you adjust quality, so you can find the point where the file is small enough but the image still looks right — rather than guessing at a quality number and re-exporting. Press Esc to clear the set.

Related and equally local: Images to PDF to assemble the results into a document, and the QR reader if the image is a QR code.