hexed

hexed is a compact console hex editor for existing files. It displays sixteen bytes per row, supports hexadecimal and character entry, and keeps changes in memory until you explicitly write or restore them.

hexed <file>

There are no command-line options. Quote a path containing spaces.

Requirements

• x64 Windows 10 or Windows 11
• Windows Terminal or another console host with VT-sequence support
• a window at least 76 columns wide and four lines high

The executable uses PE subsystem version 10.0 and is intentionally aimed at modern Windows console environments.

Editing model

hexed edits bytes in place. It never inserts, deletes, appends, or resizes the file.

Only the bytes in the visible view can be edited. Changes remain pending in memory until you press F2; F5 restores the snapshot loaded for the current view. Retyping a byte's original value removes that byte from the pending changes.

Scrolling, jumping, and resizing proceed without interruption when the destination still contains every changed byte. The pending span is rebased into the new view and remains highlighted.

A request that would move any changed byte out of view—or exit the program—is held:

changes pending in this view:  W write   R restore   Esc cancel

• W writes the pending span and continues the requested action.
• R restores the loaded snapshot and continues.
• Esc cancels an ordinary navigation request.

A resize that would exclude a changed byte has already happened and therefore cannot be cancelled; its prompt offers only write or restore.

F2 writes directly to the original file and flushes it. There is no backup and no undo after a write. If the file cannot be opened for writing, hexed opens it read-only, marks that state in the footer, and refuses data entry.

Ctrl+Break and closing the console cannot stop for a prompt. They safely discard pending in-memory changes, restore the terminal, and report the discard on exit.

Controls

Key	Action
← →	move one byte within the view
↑ ↓	move one row; scroll at the top or bottom
PgUp PgDn	move by one screen
Home End	move to the start or end of the row
Ctrl+Home Ctrl+End	move to the start or final page of the file
Tab	switch between the hexadecimal and character panes
F3	select the next configured single-byte code page
0–9, A–F	enter a nibble in the hexadecimal pane
printable ASCII	enter a byte in the character pane
F2	write pending changes
F5	restore the loaded snapshot for this view
mouse wheel	scroll three rows
left click	place the cursor
Esc Esc	request exit; pending changes still require a decision

Character-pane entry accepts bytes 20h through 7Eh. Use the hexadecimal pane to enter all other byte values.

Reading the screen

The fixed 76-column layout contains an address, sixteen hexadecimal bytes, and their character interpretation:

  offset  00 01 02 03 04 05 06 07  08 09 0A 0B 0C 0D 0E 0F  0123456789ABCDEF
00000000  48 69 21 0A FF                                    Hi!..

Changed bytes are highlighted. The real terminal caret is placed on the nibble or character that will receive the next keystroke.

The footer shows information not already visible in the dump:

• file name and size
• active character mapping, such as cp437
• read-only or MODIFIED state
• the most recent status message

Character interpretation

The right-hand pane interprets every byte through a Windows single-byte code page. The console output code page in effect when hexed starts becomes the first choice when it is single-byte, so the shell can select the initial view:

chcp 866 >nul
hexed file

F3 cycles through that captured page and the favourites compiled into HEXED_CODEPAGES in hexed.h. The supplied favourites are CP437, CP850, and Windows-1252. Unsupported, multibyte, and duplicate pages are skipped; CP437 is the fallback when the startup page is unsuitable.

Byte mappings that Windows rejects, plus Unicode C0 and C1 control characters, are shown as coloured dots rather than being sent to the terminal. Display output itself is UTF-8; the original console output code page is restored on exit.

Window behavior

The editor uses sixteen bytes per row and therefore owns a fixed width of 76 columns. It asks the terminal to take that width while running and restores the original width and height on exit. Height is dynamic: every line beyond the ruler and footer becomes another data row.

If the console host refuses resizing, a wider window is used from its left edge. A narrower window displays a size warning and recovers when sufficient space is available.

hexed uses the alternate screen buffer, leaving the shell's original screen and scrollback intact. On exit it prints one lasting summary:

hexed: C:\path\file.bin: 1 byte written
hexed: C:\path\file.bin: unchanged
hexed: C:\path\file.bin: unchanged, 3 pending bytes DISCARDED

Limitations

• Existing files only; no creation or resizing.
• Files of 4 GiB and larger are refused because addresses are eight hex digits.
• Character-pane input is printable ASCII; use hex entry for the full byte range.
• Correct startup depends on a console host delivering window-size events after the alternate screen is activated.
• Terminal resizing and restoration depend on host VT support.

Building and development

Assembler architecture, build requirements, binary-format policy, and the verification record are in DEVELOPING.md.