ImageAlchemy is a free online image compressor and converter that runs entirely in your browser. Compress, convert and resize images in bulk — no uploads, no accounts, no tracking. Everything is processed locally with WebAssembly, so an entire batch of up to 200 images never leaves your device.
Unoptimized images are the largest content type on most pages and the most common cause of slow Core Web Vitals. Converting a 2 MB JPEG to WebP at quality 80 typically yields a 400–600 KB file — a 70%+ reduction in bytes with no visible quality loss. Smaller files mean faster LCP, better crawl coverage, higher mobile rankings and less bandwidth cost.
Use quality 80 for almost everything. Between 75 and 85 the file size is still falling sharply while the visible quality cost stays imperceptible. Above 90 the file grows noticeably with no visible gain; below 60 you get banding in gradients and smearing in fine detail.
The setting is format-dependent, because the quality scales are not calibrated to each other: JPEG 78–85, WebP 75–82, and AVIF 60–75 — AVIF at 65 is frequently visually equivalent to JPEG at 80 at a smaller size. PNG is lossless and takes no quality setting at all; if you are reaching for a PNG quality slider, WebP is almost always the better choice.
Resolution matters more than quality. Resizing a 4000 px image down to the 1600 px it is actually displayed at typically removes 80% or more of the bytes and makes the image look sharper. A perfectly compressed oversized image is still a slow image. On the demo photograph on this page, the 189 KB source encodes to 112 KB at quality 80 (−41%) and 70 KB at quality 45 (−63%) — both real encodes, not estimates.
Read the full JPEG quality guide for per-format recommendations and the order to apply them in.
ImageAlchemy performs no upload at all. The codecs run locally, so your files never reach a server, are never logged, and cannot be retained — which makes the tool usable for confidential client photography, medical or legal imagery, and unreleased product shots where a cloud converter would be inappropriate.
You can verify this rather than trust it: load this page, then disable your network connection and compress an image. It will still work, because the processing is local. A cloud-based tool would fail. How client-side compression works, and how to test any tool for it.
Yes. No account, no subscription, no watermark and no file limits — batch up to 200 images at a time, as often as you like. The Pro audit is a separate one-time purchase for a different job: auditing pages you do not own.
No. Decoding and re-encoding happen in your browser using WebAssembly codecs — MozJPEG, libwebp, OxiPNG and the AV1 encoder. Your image data is never transmitted, so there is no server-side copy to lose or leak.
AVIF compresses best — roughly 20% smaller than WebP at equivalent quality — and is now supported by all major browsers. WebP remains the safe default with universal support and faster encoding. Serving AVIF first with WebP and JPEG fallbacks via <picture> is the most robust approach.
Not visibly, at the settings that matter. At quality 80 the difference from the source is imperceptible on a normal display while the file is typically 40–70% smaller. Visible damage only begins below roughly quality 60, and the artifacts appear first in smooth gradients, fine texture such as hair and foliage, and around text.
Yes. ImageAlchemy is fully responsive and works in mobile browsers, processing images locally on the device. Because nothing is uploaded, it also works over a slow or metered connection once the page has loaded.
Up to 50 MB per image and 200 images per batch. Because processing is client-side, the practical ceiling is your device's available memory rather than a server quota.
The Website Image Audit reports every image any page loads — measured, ranked by what they cost you, with the fix written out. One-time purchase, no subscription. The compressor above stays free.
Open the compression studio above, or drop your images to begin.