"Header only" might be a bad name, in my perception what it really means is "you can drop the code files into your project; we won't annoy you with our own ove

"Header only" might be a bad name, in my perception what it really means is "you can drop the code files into your project; we won't annoy you with our own over-engineered build system". Slow-compiling APIs can be made in any form, whether "header only" or not. C++ template APIs cannot be compiled separately and can cause long compile times for all transitively dependent translation units. For example, stb_image.h is a single file that is 1 copy+paste from github away. It compiles quite quickly, and often you will need it alongside only a single .c file in your project, but anyway it's extremely easy to compile it separately. All you have to do is cut+paste the implementation part to a separate .c file.