Get the data, tools (such as Fetch as Google and robots.txt Tester), and diagnostics for a healthy, Google-friendly site. Submit your sitemaps, track indexation, get crawling error and mobile usability reports, etc...
Bing Webmaster Tools provide data, reports and resources to improve your site’s performance in Bing search.
Webmaster lets you inform Yandex of new and deleted webpages, customize the indexing of your site and improve the ranking and appearance of your website in Yandex search results.
PageSpeed Insights analyzes the content of a web page, then generates suggestions to make that page faster.
Run a free website speed test from around the globe using real browsers at consumer connection speeds with detailed optimization recommendations.
Free Online Google Sitemap Generator (and validator under SEO Tools).
"Mobile-friendliness" is now a ranking factor in Google search. A page is "mobile-friendly" in Google's eye if it meets some criteria detected by Googlebot. This test will analyze a URL and report if the page has a mobile-friendly design.
The structured data testing tool checks the markup (microdata, JSON-LD, etc.) and makes sure that Google can extract the structured data from the page.
Structured Data Markup Helper shows how to update a site so that Google, and other search engines, can understand the data it contains.
Digital Marketing, Paid Search and SEO Blog. The Digital Marketing Blog that focuses on increasing revenue for companies through Paid Search, SEO, Display Ads and more from RKG. The blog is a continuing discussion of online marketing written by the employees of Merkle.
The Digital Marketing Reports are a collection of charts, data sets, and recaps from the previous fiscal quarter. Using many of our long standing clients as an index, Merkle compiles these reports to provide the industry with a set of trustworthy benchmarks that can be leveraged to inform analysts and improve advertising programs.
The Moz inbound marketing and SEO blog provides tips, tricks, and advice for improving websites and doing better search, social, content, and brand marketing.
Official news on crawling and indexing sites for the Google index.
Official Search Console Help Center where you can find tips and tutorials on using Search Console and other answers to frequently asked questions.
Extensive library of relevant SEO/SEM information complete with tools, guides, and "how to" instructions.
Stack Overflow is a question and answer site for professional and enthusiast programmers. It's 100% free, no registration required.