Every operation

Thirty-two things you can do to a file. Twenty-seven of them never send it anywhere.

Where each one runs

The badge on every row is not decoration: “in your browser” means the bytes stay on your machine, and “server” means they do not and an account is needed. Nothing here guesses.

Questions

Is “your file never leaves your computer” actually true?

For the operations marked as running in your browser, yes — they are canvas and WebAssembly code executing in the page, and no request carries your file. For the five marked as server operations it is not true, and those pages say so instead. We would rather have five honest exceptions than one claim nobody can check.

Why is there a size limit at all?

On the browser lane there is not one, beyond what your machine can hold. The 25 MB figure applies to the server lane, where the bytes have to fit in a request.