Keep resources crawlable. Blocking page resources can give Google an incomplete picture of your website. This often happens when your robots.txt file is blocking access to some or all of your page resources. If Googlebot doesn't have access to a page's resources, such as CSS, JavaScript, or images, we may not detect that it's built to display and work well on a mobile browser. In other words, we may not detect that the page is "mobile-friendly," and therefore not properly serve it to mobile searchers.
QUOTE: “Returning a code other than 404 or 410 for a non-existent page (or redirecting users to another page, such as the homepage, instead of returning a 404) can be problematic. Firstly, it tells search engines that there’s a real page at that URL. As a result, that URL may be crawled and its content indexed. Because of the time Googlebot spends on non-existent pages, your unique URLs may not be discovered as quickly or visited as frequently and your site’s crawl coverage may be impacted (also, you probably don’t want your site to rank well for the search query” GOOGLE
When referring to the homepage, a trailing slash after the hostname is optional since it leads to the same content ("" is the same as ""). For the path and filename, a trailing slash would be seen as a different URL (signaling either a file or a directory), for example, "" is not the same as "".
Since heading tags typically make text contained in them larger than normal text on the page, this is a visual cue to users that this text is important and could help them understand something about the type of content underneath the heading text. Multiple heading sizes used in order create a hierarchical structure for your content, making it easier for users to navigate through your document.
This helpful tool scans your backlink profile and turns up a list of contact information for the links and domains you'll need to reach out to for removal. Alternatively, the tool also allows you to export the list if you wish to disavow them using Google's tool. (Essentially, this tool tells Google not to take these links into account when crawling your site.)
Robots.txt is not an appropriate or effective way of blocking sensitive or confidential material. It only instructs well-behaved crawlers that the pages are not for them, but it does not prevent your server from delivering those pages to a browser that requests them. One reason is that search engines could still reference the URLs you block (showing just the URL, no title or snippet) if there happen to be links to those URLs somewhere on the Internet (like referrer logs). Also, non-compliant or rogue search engines that don't acknowledge the Robots Exclusion Standard could disobey the instructions of your robots.txt. Finally, a curious user could examine the directories or subdirectories in your robots.txt file and guess the URL of the content that you don't want seen.

Domain authority is an important ranking phenomenon in Google. Nobody knows exactly how Google calculates, ranks and rates the popularity, reputation, intent or trust of a website, outside of Google, but when I write about domain authority I am generally thinking of sites that are popular, reputable and trusted – all of which can be faked, of course.

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Experience can educate you when a page is high-quality and yet receives no traffic. If the page is thin, but is not manipulative, is indeed ‘unique’ and delivers on a purpose with little obvious detectable reason to mark it down, then you can say it is a high-quality page – just with very little search demand for it. Ignored content is not the same as ‘toxic’ content.
QUOTE: “I think there is probably a misunderstanding that there’s this one site-wide number that Google keeps for all websites and that’s not the case.  We look at lots of different factors and there’s not just this one site-wide quality score that we look at. So we try to look at a variety of different signals that come together, some of them are per page, some of them are more per site, but it’s not the case where there’s one number and it comes from these five pages on your website.” John Mueller, Google
Google ranks websites (relevancy aside for a moment) by the number and quality of incoming links to a site from other websites (amongst hundreds of other metrics). Generally speaking, a link from a page to another page is viewed in Google “eyes” as a vote for that page the link points to. The more votes a page gets, the more trusted a page can become, and the higher Google will rank it – in theory. Rankings are HUGELY affected by how much Google ultimately trusts the DOMAIN the page is on. BACKLINKS (links from other websites – trump every other signal.)
Early versions of search algorithms relied on webmaster-provided information such as the keyword meta tag or index files in engines like ALIWEB. Meta tags provide a guide to each page's content. Using metadata to index pages was found to be less than reliable, however, because the webmaster's choice of keywords in the meta tag could potentially be an inaccurate representation of the site's actual content. Inaccurate, incomplete, and inconsistent data in meta tags could and did cause pages to rank for irrelevant searches.[10][dubious – discuss] Web content providers also manipulated some attributes within the HTML source of a page in an attempt to rank well in search engines.[11] By 1997, search engine designers recognized that webmasters were making efforts to rank well in their search engine, and that some webmasters were even manipulating their rankings in search results by stuffing pages with excessive or irrelevant keywords. Early search engines, such as Altavista and Infoseek, adjusted their algorithms to prevent webmasters from manipulating rankings.[12]
You should build a website to benefit your users, and any optimization should be geared toward making the user experience better. One of those users is a search engine, which helps other users discover your content. Search Engine Optimization is about helping search engines understand and present content. Your site may be smaller or larger than our example site and offer vastly different content, but the optimization topics we discuss below should apply to sites of all sizes and types. We hope our guide gives you some fresh ideas on how to improve your website, and we'd love to hear your questions, feedback, and success stories in the Google Webmaster Help Forum1.