can anyone recommend how to perform a responsiveness check on a website?

For this task, I can recommend using website responsive checker "WebsiteResponsiveTest". The "WebsiteResponsiveTest" responsive checker tool helps to identify not only visual issues, but also functional limitations on different devices. This enables developers to optimize the site for all possible usage scenarios, which is a key aspect in modern web development. I hope that I was able to help you with this issue. Good luck with using this solution!