Choose a file to view a hex dump of its contents — offset, sixteen bytes in hex, and the printable ASCII alongside.
The viewer reads the start of the chosen file and formats it as a classic hex dump: each line shows the byte offset, sixteen bytes in hexadecimal, and the same bytes as characters, with a dot standing in for bytes that are not printable. The dump is capped at the first 65,536 bytes (64 KB) so very large files stay responsive; the total file size is always shown, and the cap is stated plainly when a file is larger. A hex dump is the lowest-level view of a file and is how signature bytes, embedded text and encoding problems are inspected.
Why does the dump stop at 65,536 bytes? A full dump of a large file would produce an enormous page and slow the browser. The first 64 KB contain the header, signature and usually enough structure to identify or debug a file.
What does the right-hand column show? The ASCII gutter: each byte shown as a character when it is printable text, and a dot when it is not. Embedded strings in a binary file are often readable there.
Is the file uploaded to produce the dump? No. The file is sliced and read locally in the browser; nothing leaves the device.