AltHex
Hex editor for files of any size, disks and firmware
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About
AltHex is a hex editor for files of any size, disks, disk images and firmware. A file of any size opens at once, because AltHex reads only the parts you look at, and edits are written only when you save. It recognizes PNG, ELF, PE, ZIP, file systems and many other formats and shows their fields as a tree; you can describe your own formats in a C-like template language. It compares files and makes patches, computes CRCs and hashes, opens disks read-only, and disassembles STM32, AVR and ESP32 firmware. Programs and AI agents can work with it over MCP and a local API, and there is a command line for batch jobs.
Features
- Open source (MIT)
- No dependencies
- Single executable file
- Files of any size
- Unlimited undo and redo
- Keyboard shortcuts
What it does
Opens files of any size
A 50 GB file opens at once. Insert, delete or overwrite bytes, with no limit on undo.
Shows the structure
Recognizes PNG, ELF, PE, ZIP, PDF, MBR, GPT, FAT, NTFS, ext4 and more, and shows the fields as a tree you can edit.
Your own templates
Describe a format in a C-like template language close to 010 Editor Binary Templates.
Compares and patches
Compares two files side by side, even with shifts, and makes or applies IPS, BPS and text patches.
Hashes and checksums
CRC-8 to CRC-64, Adler-32, MD5, SHA-1, SHA-2, BLAKE3 and your own CRC, plus entropy and a byte histogram.
Opens disks
Reads disks read-only, shows partitions and file systems, extracts files. Unreadable sectors do not stop the work.
Looks into firmware
Intel HEX, S-record, UF2, DfuSe and ESP images: a listing for ARM, AVR, RISC-V, Xtensa and x86, vectors and registers named.
Works with AI agents
MCP and a local JSON-RPC API let other programs read, search and propose edits, which you approve.
Speaks your language
Available in 12 languages, with a light or dark look.