What about other search engines that use them? Hang on while I submit my site to those 75,000 engines first [sarcasm!]. Yes, ten years ago early search engines liked looking at your meta-keywords. I’ve seen OPs in forums ponder which is the best way to write these tags – with commas, with spaces, limiting to how many characters. Forget about meta-keyword tags – they are a pointless waste of time and bandwidth.
QUOTE: “Supplementary Content contributes to a good user experience on the page, but does not directly help the page achieve its purpose. SC is created by Webmasters and is an important part of the user experience. One common type of SC is navigation links which allow users to visit other parts of the website. Note that in some cases, content behind tabs may be considered part of the SC of the page.” Google Search Quality Evaluator Guidelines 2017
Google used to make much of its ad hoc keyword search functionality available as well, but now the Keyword Planner is behind a paywall in AdWords as a premium feature. Difficulty scores are inspired by the way Google calculates its Competition Score metric in AdWords, though most vendors calculate difficulty using PA and DA numbers correlated with search engine positions, without AdWords data blended in at all. Search Volume is a different matter, and is almost always directly lifted from AdWords. Not to mention keyword suggestions and related keywords data, which in many tools come from Google's Suggest and Autocomplete application programming interfaces (APIs).
QUOTE: “Medium pages achieve their purpose and have neither high nor low expertise, authoritativeness, and trustworthiness. However, Medium pages lack the characteristics that would support a higher quality rating. Occasionally, you will find a page with a mix of high and low quality characteristics. In those cases, the best page quality rating may be Medium.” Google Quality Evaluator Guidelines, 2017
Google will INDEX perhaps 1000s of characters in a title… but I don’t think anyone knows exactly how many characters or words Google will count AS a TITLE TAG when determining RELEVANCE OF A DOCUMENT for ranking purposes. It is a very hard thing to try to isolate accurately with all the testing and obfuscation Google uses to hide it’s ‘secret sauce’. I have had ranking success with longer titles – much longer titles. Google certainly reads ALL the words in your page title (unless you are spamming it silly, of course).
QUOTE: “alt attribute should be used to describe the image. So if you have an image of a big blue pineapple chair you should use the alt tag that best describes it, which is alt=”big blue pineapple chair.” title attribute should be used when the image is a hyperlink to a specific page. The title attribute should contain information about what will happen when you click on the image. For example, if the image will get larger, it should read something like, title=”View a larger version of the big blue pineapple chair image.” John Mueller, Google
Google has a LONG list of technical requirements it advises you meet, on top of all the things it tells you NOT to do to optimise your website. Meeting Google’s technical guidelines is no magic bullet to success – but failing to meet them can impact your rankings in the long run – and the odd technical issue can actually severely impact your entire site if rolled out across multiple pages.
Being ‘relevant’ comes down to keywords & key phrases – in domain names, URLs, Title Elements, the number of times they are repeated in text on the page, text in image alt tags, rich markup and importantly in keyword links to the page in question. If you are relying on manipulating hidden elements on a page to do well in Google, you’ll probably trigger spam filters. If it is ‘hidden’ in on-page elements – beware relying on it too much to improve your rankings.
Sometimes, Google turns up the dial on demands on ‘quality’, and if your site falls short, a website traffic crunch is assured. Some sites invite problems ignoring Google’s ‘rules’ and some sites inadvertently introduce technical problems to their site after the date of a major algorithm update and are then impacted negatively by later refreshes of the algorithm.
Thank you for the great checklist. It is really useful and gave us a couple of new hints on optimization process. We’ve been using WebSite Auditor and found it exremely helpful in site’s structure and content analysis, bringing all the statistical information on the validation errors, social mentions, duplicate stuff, etc. under one roof. Still there is so many different SEO information you sometimes cannot understand what to start with. Fortunately you answered this question. Thank you again!