Tools for the decisions, not just the files
Most website to app tools generate assets. These are built around the questions that come up when a site becomes an app: is it ready? what should it be called? what will the status bar look like? which permissions does it honestly need? what happens when the connection drops? will Play accept the listing? Each tool answers one of them in the browser and hands you the output — a score, an icon, a block of XML, an HTML file — to use in the builder or in a native project.
None of them uploads anything. Icons are drawn on a canvas, previews are rendered locally, checks run on the text you type. They work offline once loaded, and nothing you enter is stored or sent.
If you would rather skip the pieces, the builder takes a website URL and returns a signed Android app in a few minutes, generating the icon set, the theme and the manifest for you. These tools are for seeing the pieces first — and for the details the builder cannot decide on your behalf.