If you have a recent vintage receiver or amp and your speakers are not regularly connected to your computer, I suggest checking its manual as may newer audio components already have this function built-in. Some even include a calibration device. If your speakers are attached to your computer free audio test sites exist on the web. Just do a browser search for "Audio Test Websites". The first site that I found but not used is "https://www.audiocheck.net/" . There are literally dozens more.
For those that feel I am unfairly targeting a developer, I feel that such developers are exploiting uninformed users for a source of income. I would encourage them to instead focus their development on applications for which their might be a real need, ethically creating an income stream for themselves.