How to make a free web app safe liability-wise?

I want to provide a free web application to researchers to conduct their behavioral experiments online during the Corona pandemic (many labs are closed for the foreseeable future). It runs the experiments and stores the collected data (from the participants) in a database and file system. It's all set up from the technical side (jatos.org) but since I'm a programmer I have no clue about law and regulations. I do not expect any trouble (researchers are usually rather kind) but I wonder what is the minimal stuff I should put into my app to make it safe liability-wise? I searched around but couldn't find anything but long EULA like agreement that seem to me too much for this temporary free web app.