A hex editor (or binary file editor or byte editor) is a type of computer program that allows a user to manipulate the fundamental binary (0 / 1, zero / one) data that makes up computer files. The name 'hex' comes from the fact that hexadecimal is the standard numerical format for digital data on a screen when editing at this level. Note that computer files can be very small (just a name, with no content) to very large (content spanning multiple hard disks). A typical computer file occupies multiple areas on the platter(s) of a disk drive, whose contents are put together to form the file. Hex editors that were designed to read ("parse") and edit sector data from the physical segments of floppy or hard disks were sometimes called sector editors or disk editors.

By using a hex editor, a user can see or edit the raw and exact contents of a file, as opposed to the interpretation of the same content that other, higher level application software may associate with the file format. For example, this could be raw image data, in contrast to the way image editing software would interpret and show the same file.