There are some hex editors for Mac available but only Synalyze It! allows to create a grammar for automatic file decoding in a specialized grammar editor.

Synalyze It! - a Mac Free Hex Editor for macOS Professionals I doubt that I will ever fully exploit the potential of Synalyze It! but the value I’ve received is already many multiples of the price I paid. I was sent a complete solution to my problem that also served as an advanced Synalyze It! tutorial. When I emailed a question to the developer, the technical support was outstanding. A hex editor is not for everyone or for every. I quickly got ambitious and was soon in over my head exploring Synalyze It!’s features. Hex Fiend is one of those indispensable tools that making poking and prodding software bits on the Mac so great. If the standard formatting tools are not enough, you can write formatting scripts using Python or Lua. Your files can even modify the formatting, allowing you to create settings on the fly to variably view your data. Instead of struggling with cryptic lines of hexadecimal, you can view and label data values as floating point or integer, signed or unsigned, with any byte length. With Synalyze It!, you can create custom data formatters for your personal binary files. That alone is useful but, if you’re a programmer creating a custom binary file format, Synalyze It! is priceless. Synalyze It! provides formatters for common binary types like ICC, PNG, TIFF, WAV, ZIP and dozens more. It enables you to easily apply a structured format to your file bytes and convert them into meaningful displays of data. Synalyze It! is an extremely flexible and useful tool for viewing binary file data.

Hex editor mac os x