Hex Fiend

Hex Fiend edits binary files without loading them fully into memory, so even huge files open and scroll quickly. You can insert and delete bytes rather than only overwrite them, search, inspect values in different number formats, and compare two files with insertions taken into account.

Binary templates written in Tcl describe file formats and display their structure. The editing engine is also available as a framework for other apps. The most recent release, 2.18.1, is from March 2025.