imgix Page Weight Tool
imgix Page Weight Tool measures the resources on your site and then recommends how to improve your site’s load time.
Yellow Lab Tools
Free online web performance tool. Audit your webpage for performance and front-end quality issues. And it's open-source!
WAVE Web Accessibility Tool
Nibbler
Free tool for testing how good your website is, and what you can do to improve it. Check accessibility, SEO, social media, compliance and more.