2021 seo periodic table by Search Engine Land

2021 SEO Periodic Table (Compared to 2019)

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Search Engine Land’s updated 2021 SEO Periodic Table is now live – Download the table via their website: https://searchengineland.com/seotable.

What’s New Since the Last Update?

Since the last Periodic Table of SEO Factors for 2019, there have been a few changes including new weight rankings, new elements and even new categories.

  • New Weight Rankings – In 2019 the weight rankings were on a scale of -3 (harmful to SEO) to +3 (beneficial), but this has now been expanded to a range of -5 to +5 to fit the scalability of new elements. 
  • New but excluded Category – Although it’s not included in the 2021 Periodic Table, AI (Artificial Intelligence within a new category of ‘Global’) should be an element of every SEO strategy. By utilising AI, you can work more efficiently – such as automating content briefs, automating keyword research and even automating metadata tags.

Below are some additional notes on changes to elements within each category and why this is important for your SEO strategy in 2021 and beyond.


Quality (+5) is now the highest weighted element within the content category (previously even with other elements at +3) and is arguably the highest-ranking factor among all SEO elements.

The other change is the increased weight of Answers (+4) (previously +2) which rewards websites creating content that satisfies user search intent.

These two subtle updates reflect the need for every SEO strategy to include effective content marketing that answers user’s queries.


Moving across from the HTML category, the Structure (+4) element continues to be important by ensuring your website is easy to navigate and understand by users and bots.

The other major change is the introduction of the new Parity (+4) element, which compares differences between mobile and desktop experiences. Hint: there should be no difference.

These elements, combined with Mobile First (+4), continue to highlight the importance of a seamless, user-friendly experience across devices.


There were several changes within the HTML category as technologies continue to rapidly evolve, even over the 2 years since the last Periodic Table.

With the shift of the Structure element to the Architecture category, Schema (+4) now has its own place within HTML (previously it was a part of the Structure element) to help turn data into enhanced listings such as featured snippets in SERPs. 

Another change was the introduction of Content Shift (+2), to minimise poor user experience during a page load. Known as Cumulative Layout Shift (CLS) within Google’s Core Web Vitals guidelines, this can be improved with changes to HTML and other code snippets.

The other new addition was Image Alt (+1), which describes image content to improve accessibility and SEO for visually impaired users and bots. 

Finally, the removal of AMP, which was Google’s mobile page format build for speed, means web developers no longer need to invest in this.

These changes signal the importance of HTML accessibility and how bots can easily access and interpret your website information. 


A new category, based on Google’s core updates, contains the elements of Expertise (+5), Authoritativeness (+5) and Trustworthiness (+4).

These essentially define the value and relevance of websites and how content should be interpreted by users and bots.

In summary, your content should showcase itself as a thought leader and why that information should be trusted (i.e. get valuable backlinks, social shares, testimonials and other signals).


This category has been around the longest with no major changes since the last Periodic Table update.

The takeaways here are to continuing gaining quality links from trusted websites and continue using descriptive link text.


There were a few minor changes to this category, most notably the increased weighting of Intent (+4) (previously +1) which focuses on why the user is searching.

The other notable change was the removal of History (+1) and the addition of Engagement (+1) which was a shift in algorithm focus from how regularly users visited your website to how users interacted with or bounced from your website.

Tying into the Content and Reputation categories, you should start seeing a consistent theme that ranking factors want the user to be satisfied once they arrive at your website – so focus on this!


The previous 6 elements within the Toxins category (from 2019) have been expanded on and given a wider range of weightings.

Cloaking (-5) continues to be the most harmful element, which shows bots and search engines different content than what users see.

Schemes (-4) continues to be the second most harmful element, which includes buying links and spamming blogs.

Then new elements of Bad Content (-4) and Malicious Behaviour (-4) are added to the category, where search engines punish automated or scraped content and phishing or malware websites.

The remaining 4 Toxins have similar definitions and weightings. 

To avoid these penalties, don’t be deceitful to search engines and users, don’t try to manipulate rankings and don’t steal content or information from others.


This is a separate section within the SEO Periodic Table, due to the specific areas of SEO they impact.


The elements and weightings within this ‘category’ are contentious amongst local SEO experts.

While having a Google My Business (+5) is required to be found on Google Maps, Bing uses Bing Places (+?) and other apps use other databases. Therefore, for the category of Local, this element is not the top ranking factor. 

Locations (+5), Citations (+3) and NAP (+3) are warranted as elements and are correctly weighted.

Reviews (+3) is arguably the strongest local ranking factor especially when customers include keywords within their reviews and business owners respond to each review.


This is another contentious ‘category’ as it includes Top Stories (+4) and Discover (+4) which are platforms used to maximise organic traffic and not (by definition) elements or ranking factors. To feature on these platforms you need to optimize your website following the rest of the Periodic Table elements.

The remaining elements overlap with other categories or elements around image optimisation, architecture and website structure, and content accessibility.

Therefore, this ‘category’ is more of a guide than a group of elemental ranking factors.


The final Niche category mostly includes important ranking factors and elements for ecommerce, given that ecommerce SEO is different to SEO for information-based websites.

Product Descriptions (+5) is arguably not the top ranking factor for ecommerce as there are examples of successful websites selling products without extensive product descriptions. But that doesn’t mean you should ignore it! It’s still important and should be optimised.

Structured Data (+4) is also not a top-ranking factor or element for ecommerce success. However, Product markup does help search engines better understand the products, offers and reviews and help serve these as rich snippets in SERPs.

Finally, like Google My Business for Local, Google Merchant Centre (+4) is a platform for ecommerce owners to manage product inventory, data feeds, stock levels and more. Therefore this is not a ranking factor for ecommerce product URLs to appear in organic search. However, to utilise Google Shopping (another search opportunity) you will require an optimised Merchant Centre account.

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