Hex Viewer shows a file or some text as the familiar three-column hex dump: the offset, the bytes in hexadecimal, and the printable ASCII with non-printable bytes shown as a dot.
The file is read with the browser File API and never uploaded.
Yes. Input that looks like hex (with or without spaces or 0x) is read as bytes; anything else is treated as UTF-8 text.
Large files are handled, but only the first 64 KB is shown to keep the page responsive.
No. It is read and dumped in the page.
Printable characters (0x20 to 0x7e); every other byte is a dot.