Have a static lib, is there a simple way to know it is for 32 bit or 64 bit?

Run a visual studio command prompt to ensure your path can find dumpbin.exe

Pipe to findstr to save on the big spew about each section and optionally you can use a wildcard to analyse a folder of libs.

dumpbin /headers *.lib | findstr machine

Example of what you're looking for;

8664 machine (x64)

You can use dumpbin utility with /headers option

It returns whether the library was built for 32 or 64 bit architecture.

Check DUMPBIN Reference for details.

Example usage:

c:\>dumpbin libXYZ.lib /headers