Images are where most of the weight of a web page comes from, and almost every image task turns out to be one of a handful of jobs: make the file smaller, change its dimensions, change its framing, change its format, or put several of them into one document. The tools below cover all five, and none of them asks you to upload anything — the pixels are processed by your own machine.
Compress
Resize and crop
Convert
Why these tools work without a server
For twenty years, editing an image in a browser meant uploading it to somebody else's computer, waiting, and downloading the result. That is no longer necessary. Browsers now expose the same two primitives an image editor needs — a canvas that can decode, draw and re-encode an image, and a compression module that can write JPEG, PNG and WebP — and both of them run locally, at full speed, with no network involved.
The consequences are worth spelling out. There is no upload, so a photo never leaves your device and there is no copy of it on anyone's server. There is no queue, so processing starts the moment you drop a file in and a batch of twenty images finishes in seconds. There is no file size limit imposed by a hosting plan, only the memory of your own machine. And there is nothing to sign up for, because there is no account to keep in sync with a backend.
The one thing you give up is server-side muscle. A very large image is processed by your laptop or phone rather than a machine in a data centre, so a 50 megapixel RAW file will take a noticeable moment. For photographs, screenshots and product images — which is what almost everyone is actually working with — that trade is invisible.
Which format should you end up with?
WebP is the sensible default for anything going on a web page: it is smaller than JPEG at the same visual quality, it supports transparency, and every current browser displays it. JPEG remains the safest choice when the file is going somewhere you do not control — an upload form, a print shop, an older content management system — because nothing has ever failed to open a JPEG. PNG is the right answer when the image must stay pixel-exact: screenshots, charts, logos, anything with flat colour or sharp edges that JPEG would blur. Converting a photograph to PNG will usually make it several times larger for no visible gain, which is why the PNG tools here are honest about what they can and cannot shrink.