If you are seeing this page because a link would not load, you are offline and that page was not stored yet. Anything listed below as available offline still works.
Why this is possible here and not elsewhere
Every tool on this site already runs inside your browser rather than on a server, so there is no request to fail when the network goes away. All that is missing offline is the application itself, and that can be stored ahead of time. A site that processes your files on a server can never do this, however good its offline page looks: without a connection there is nowhere for the work to happen.
Choose what to keep
Grouped by what you would actually want, rather than by file. The text, data and developer tools cost almost nothing. PDF tools need a worker of about a megabyte and a half, which is the group worth taking before a flight. Background removal needs its models, which is tens of megabytes, so it is opt-in rather than something you are charged for on a first visit.
Everything that needs no binary: counters, converters, formatters, hashing, colour, cron, timestamps.
Merge, split, rotate, compress, watermark, sign, protect and unlock, plus page extraction. This is the group that makes a long flight useful.
Resize, crop, rotate, flip, compress, convert, watermark, DPI and upscaling. All canvas work, so the cost is just the pages.
The segmentation models and the WebAssembly runtime they need. The largest group by far, and worth taking only if you expect to cut out images without a connection.
Installing it as an app
Your browser will offer to install the StuHub once you have used it a little: look for an install icon in the address bar on desktop Chrome or Edge, or "Add to Home Screen" on mobile. Installing gives it its own window and makes the offline behaviour more reliable, because an installed app is less likely to have its storage reclaimed.
What is stored, and what is not
Only the application: pages, scripts, and the binaries listed above. Your documents and images are never stored, because they are never uploaded and never written to a cache. Clearing offline data removes the application copy and nothing else, and every tool keeps working normally while you have a connection.
Before storing anything large, the site asks your browser for persistent storage. Without that, a browser short on space treats a cache of model weights as the first thing to reclaim, which is how people discover their offline tools are not there when they need them.