Open the executable in a hex editor (like HxD or 010 Editor) and search for the string MEI or PYI near the end of the file. For PyInstaller ≥4.x, look for the cookie pattern:
MEI\014\013\012\016\017\021\003\004\005
If you can’t find any recognizable magic bytes, the file is either not a PyInstaller executable or is packed. Open the executable in a hex editor (like
To understand the error, you have to understand how PyInstaller works. If you can’t find any recognizable magic bytes,
Obvious but worth stating: if the file was built with PyInstaller, the cookie exists. However, many people run the extractor on UPX-packed files, non-PE (Portable Executable) files, or even DLLs. Always verify the file type first: Scenario: Works on dev machine but not on end-user machine
file my_executable.exe
PyInstaller has evolved over time. The cookie format changed significantly between versions:
Most extraction tools were written for PyInstaller ≤3.x. If your target was built with PyInstaller 4, 5, or 6, the tool likely won’t recognize the cookie.