There are many reasons why websites fail to load. For example, the internet not working, server-side issues, web browser issues, etc. While the browser and internet issues can be easily fixed on Windows, there is nothing you can do if the site has a problem on the server side. Here is list of some best websites, that can show if website is down or not.
1. Google PageSpeed Insights
2. GTmetrix
4. Upward trend
5. For everyone or just for me
6. Pingdom
8. SiteChecker
10. isitwp