Google webmaster tools: Google webmaster tool is a free SEO tool offered by Google. It is a set of SEO tools that allow you to control your website. It informs you if anything goes wrong with your website like crawling mistakes, plenty of 404 pages, malware issues, manual penalties, etc. In other words, Google communicates with webmasters through this tool. You also do not need to use most of the expensive SEO tools if you are using this tool.
Google Analytics: It is a freemium web analytics service offered by Google. It provides the detailed statistics of the website traffic. It was introduced in November 2005 to track and report website traffic. It is a set of statistics and analytical tools that monitor the performance of your site. It tells you about your visitors and their activities, dwell-time metrics, search terms or incoming keywords and more.
Open site explorer: This tool provides stats such as overall link counts and the count of domains that are linked to a URL including the anchor text distribution.
Alexa: It is a ranking system that ranks the websites by web traffic data. The lower the Alexa rank, the more will be the traffic.
Website grader: It is a free SEO tool that grades the websites on some key metrics such as security, mobile readiness, performance, and SEO.
Google Keyword Planner: This tool of Google comes with many features. It gives you an estimation of traffic for your target keywords and suggests keywords with high traffic. Thus, you can shortlist the relevant keywords from the list of keywords offered by this tool.
Plagiarism Checker: There are various tools to check the plagiarized content such as smallseotools.com, plagiarisma.net and more. Using these tools, you can avoid duplicate content and upload the unique or original content on your site.