1) Google Analytics

Google Analytics allows webmasters to track user behavior as they navigate the site, as understanding user behavior is critical to optimizing your site. It collects data automatically and offers customizable reports to better understand user behavior completely free of charge.

2) Google Search Console

Allows webmasters to view the performance of their website on Google, helps to troubleshoot your website, fix indexing issues, request re-indexing for new content, and a host of other features. But an important component of the console that makes it invaluable to webmasters is its ability to provide search-related data.

3) Google Optimization

If you’re looking for a free A/B testing tool for your website, Google Optimization is the way to go, you won’t find anything better. And it also integrates seamlessly with Google Analytics.

4) Hotjar

Hotjar is an all-in-one quality data collection tool. Hotjar offers webmasters and SEOs a variety of tools to help you create heatmaps, track funnels, and user surveys. It is easy to use and is absolutely free.

5) PageSpeed ​​Statistics

Another free tool offered by Google, PageSpeed ​​Insights is used to measure the performance of a website on desktop and mobile devices. PageSpeed ​​results provide webmasters with an accurate view of how users are interacting with a website.

6) Screaming frog

Screaming Frog is a crawler that crawls your site to identify common SEO issues. It finds broken links, detects duplicate content, finds redirects, extracts relevant data from a web page, parses page titles and meta tags.

via entrepreneur.com