Markup Validators:
- Facebook Sharing Debugger
- Facebook Microdata Debug Tool
- Google Rich Results Test
- LinkedIn Post Inspector
- Pinterest Rich Pins Validator
- Twitter Card Validator
- Schema Markup Validator
- W3C Markup Validator
- Google PageSpeed Insights - recommended for general site and webpage health checks (results influence SEO ranking).
- Google's Search Engine Optimization (SEO) Starter Guide - essential reading to understand Google SEO ranking factors.
- Webpage Performance Test with Waterfall - recommended to check and diagnose basic performance issues.
- SSL Server Test by SSL Labs - recommended test for any site using https.