Should we include tool usability evaluation based only on the research team opinions in the paper?
We decided to describe the tool in a paper and attempt to publish it. 


Why do you want to publish the description? Do you expect that other people will want to use this exact tool? Then you may need somebody outside the original team to evaluate it. Do you expect that nobody will use this exact tool, but the ideas and concepts might be useful to others in developing their own tools?  Then the usability aspect is probably irrelevant.