SEO Minion is a free Chrome (and Firefox) extension that lets you analyze a page's On-Page SEO, check for broken links, and preview your content in search results.
PageSpeed Insights is a tool created by Google that measures the loading speed of a page on mobile and desktop. The tool highlights areas for improvement to have a faster site.
Google Trends allows you to measure the number of searches for a term typed in the Google search engine, its evolution over time, the regions in which it is most popular and the associated queries and topics.
1.fr analyzes the text of a web page to determine if it is rich enough in content. The tool also suggests keywords that might be present depending on the content.
Find out what people search for on Google based on a keyword. Limited to 3 requests per day in free version. French equivalent of the famous AnswerThePublic.
Ubersuggest is a comprehensive SEO tool that helps improve content creation. Ubersuggest suggests keyword ideas, generates a report on top ranking pages and backlinks. The tool is limited in its free version.