“Sometimes, your site will need some downtime, so you can fix things or update plugins. Most of the time, this tends to be a relatively short period in which Google will most likely not attempt to crawl your website. However, in the case that you need more time to get things fixed, chances are much higher that GoogleBot might come for a visit and be confronted with a website that’s down. So how do we prevent Google from deranking your website?”

Source: HTTP 503: Handling site maintenance correctly for SEO • Yoast

There are several common HTML errors that can negatively impact the search engine optimization (SEO) of a website. Some of the most common HTML errors and their impact on SEO are:

1. Missing or Incorrect Meta Tags: Meta tags provide important information about a webpage to search engines, such as the page title and description. Missing or incorrect meta tags can lead to confusion for search engines and result in a lower ranking for the page.
2. Broken Links: Broken links, which are links that lead to pages that no longer exist, can harm the user experience and hurt SEO. Search engines may see a website with a lot of broken links as low-quality and less trustworthy.
3. Missing Alt Tags: Alt tags provide text descriptions of images on a webpage. If alt tags are missing, search engines may not be able to understand the content of the images, which can negatively affect the website’s ranking.
4. Duplicate Content: Having duplicate content on a website can result in a lower ranking because search engines may not know which version of the content is the original. This can lead to a penalty and a decrease in search visibility.
5. Slow Loading Speed: Slow loading speed can negatively impact user experience and result in a lower ranking. This is because search engines prioritize websites that offer a fast and seamless user experience.
6. Incorrect Use of Header Tags: Header tags, such as H1, H2, and H3, are used to structure content on a webpage. Incorrect use of header tags can make it difficult for search engines to understand the content and negatively impact SEO.

Overall, it’s important to make sure that a website’s HTML is free of errors to maximize its potential for search engine optimization.