www.easybib.com is a great website evaluation tool! Just copy and paste a web address into the "Autocite" bar and click "Cite this." Then check to see whether or not EasyBib says the website is credible. Take a look at the See Examples PDF you can download, and/or the checklists that guide you through evaluating the website yourself if it's not one that EasyBib has evaluated before. If it's a website that EasyBib does not recognize, you can scroll to the bottom and click on the Website Evaluation button.
Here is a PDF file that shows great examples of how to evaluate a website, complete with a chart at the end to summarize what to look for: