LÖVE

What's the best practice to determine hard- and software requirements for your game?

For example, something like this:

Minimum
[*]OS:Windows 7/Windows 8
[*]Processor:Intel® Pentium® IV 2.4 GHz eller AMD 3500+
[*]Memory:2 GB RAM
[*]Graphics:NVIDIA® GeForce 8800 or ATI Radeon® X1900, 512mb video memory required
[*]DirectX®:9.0c
[*]...

Recommended
[*]OS:/Windows 7/Windows 8
[*]Processor:Intel® Pentium® IV 2.4 GHz or AMD 3500+
[*]Memory:2 GB RAM
[*]Graphics:NVIDIA® GeForce 8800 or ATI Radeon® X1900, 1024mb video memory recommended
[*]...

Are there any tools available or is it just "trial and error" with different setups?

Log your game's performance during a play test.
For memory, on windows at least you can use perfmon to record memory usage. https://success.scribesoft.com/s/articl ... mory-Usage
For getting the amount of texture memory on the video card you can call love.graphics.getStats().

For one, the baseline should be dictated by the löve version you use.

The GPU needs to support a specific OpenGL or OpenGL ES version, and forget about DirectX, it's completely irrelevant here since it's not used at all. (because OGL has cross-platform support, and DX doesn't)

For the other things, CPU depends on the complexity of your code, and Memory and Video Memory depend on the number of graphical assets you have, and how big they are in terms of image dimensions; additionally, the lowest video card supported could be raised by you wanting to use larger textures; löve 11.x may run with an older GPU, but it may not support texture sizes you want to have.

Edit: Also, Shaders are another big part of what your recommended and minimal supported GPU should be.

There are also some functions löve has that you can make use of:
love.graphics.getStats
love.graphics.getSupported
love.graphics.getSystemLimits
love.graphics.getTextureTypes
and some more, found on the wiki.

Sounds like i have to do a lot of homework.

I presume you mean "Recommended" instead of "Maximum". Are you going to say "you can't run this game with anything better than these specs"?

You are right, should be "Recommended".