View a file as a hex dump without uploading it

The argument for staying local is at its strongest on this page, because the whole reason to open a hex view is that you do not know what the file is. An unexpected attachment, a download that will not open, an export from a system nobody documented. Handing an unidentified file to a third party is a move nobody would make deliberately, and it is the default behaviour of any hosted viewer.

What you learn is usually immediate. The first few bytes of a file identify its real format regardless of what the extension claims, so a document that refuses to open turns out to be a renamed archive, or an error page that was saved with the wrong name, or a file that is empty apart from a few bytes of whitespace. A byte order mark at the start explains a surprising share of parser failures.

The end of the file is worth as much as the beginning. Many formats close with a recognisable structure, so a file that simply stops is a download that did not finish, which saves you from debugging the wrong problem entirely. Between the two ends, the printable column tells you quickly whether you are looking at text, compressed data, or something encrypted.

Confirm the file stayed put by opening it with the network disconnected: the bytes appear anyway. That is the point of doing this locally, and it also means you can inspect something you actively distrust without giving it any opportunity to be somewhere else.