YSlow

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SEMRush

Pingdom is a web-based tool for monitoring website performance and availability. Their service is used by over 30,000+ users including startups and 60% of the Fortune 500 companies. Pingdom can help digital marketers understand the impact performance has on reach and sales, or web developers and devops teams to identify bottlenecks and monitor impact of their latest push to production.

With WebPageTest you can run a free website speed test from around the globe using real browsers at consumer connection speeds with detailed optimization recommendations.

GTmetrix is free, web-based website performance monitoring tool. With GTmetrix you can see how your site performs, reveal why it's slow and discover optimization opportunities.

The Swiss Army knife of content marketing, Ahrefs is a set of SEO tools packaged as a service. With Ahrefs, content marketers SEO's can get detail search engine data about their domains, which can be used to further improve the visibility and reach online. The toolset is powered by AhrefsBot, a web crawler that crawls webpages and provide data to analyze both organic and paid results in search engines. Ahrefs is loved by content marketers across the globe, that use the tool for competitor analysis, backlink checking, SERP monitoring and much more.

With SERPStat SEO's can monitor and improved search engines rankings. SERPStat is a web-based SEO service provider that includes all tools necessary to do keyword research, backlink analysis, domain analysis and much more.

Ubersuggest is freemium SEO tool that helps search engine marketers to generate keyword ideas for their content marketing strategy and production. With Ubersuggest freemium keyword tool, it is possible to generate a limited number of suggestions for free and take content creation to the next level while increasing website's chances of ranking against the competition. Ubersuggest is released by the popular SEO guru Neil Patel, and was previously provided as a 100% free SEO software.