Website SEO anaylysis and audit tool.
For the websites that I have checked, says that the information is too old to show. Then requires me to refresh. Then there is the button for a 7 day free trial and a paid subscription after that.
4 stars because it's not extension, but bookmark. Otherwise. Excellant analyzing tools gives advices and tips on improviing.
https://www.seoquake.com/
https://petasittek.com
SEO Tester Online
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https://semalt.com