Valid HTML for More Effective SEO

Valid HTML markup, free of errors and warnings, is essential for SEO performance.

Valid HTML for More Effective SEO

SEO Principle: HTML markup should be valid and free of errors and warnings.

HTML markup errors remain an impediment to better SEO performance for many websites — probably most websites. The importance of correct HTML shouldn't come as a surprise, and yet valid HTML remains undervalued by web designers, HTML template vendors, most "build your own website" companies, and SEO consultants and other SEO practitioners. (If you maintain your own website, and if you want your website to show up in the search results when people search for relevant keywords — or even simply your business name — you're an SEO practitioner).

7 Reasons Why HTML Validation is Important for Effective SEO

This principle is supported by a variety of observations about the importance of valid HTML markup for effective marketing campaigns and search engine optomization efforts. Here are seven really great reasons why valid HTML markup should be a core principle of your website development.


Faster is Better than Slower

HTML errors make web pages load slower, corroding your SEO page-rank.

Invalid HTML markup means web browsers must do more work to guess about how to render the page. Correct, valid, and error-free HTML, by contrast, is easier for browsers to render and results in faster page loads, sometimes significantly faster.

Web indexing engines like Google and Microsoft Bing have long paid careful attention to page load speeds. What web designers already realize this isn't simply a function of a fast server on a fast network — that's why they strive to load only necessary Javascript on a given page, and use scripts to "minify" CSS stylesheets. Loading a bunch of uneccessary spaces and tabs has a multiplier effect!

Web design industry best practices for SEO have long included spending valuable time of web designers to minify CSS, and yet industry tolerance for malformed HTML remains shockingly high.

Correct HTML markup should be a key part of any SEO campaign, for this reason, alone. There are several other reasons, each as important.

Indexed is Better than Invisible & Ignored

Search engines, especially Google, examine the HTML structure of HTML pages looking for clues to meaning which help create a better index of your website — and increase the chances that the information on your website will reach the people who are looking for it.

Certain HTML errors can confuse the parser which may accidentally hide part of the content of the web page from the index (if the web spider gives up trying to understand the page, and moves on, for example). Content on the page might simply be ignored because the web robots can't parse the HTML.

It's not merely difficult to optimize your content for search engines, if your content isn't able to be indexed due to a typo, unclear nesting from unclosed tags, or other invalid markup in the HTML. It's impossible!

Valid HTML is Resilient

Errors in HTML markup make web pages, websites, and web apps brittle.

The document page structure can break when new content is added or changes are made, such as adding menu items, containers, or page sections, or when adding new elements to a section. Fluid web designs become clunky and produce unexpected results on different screen sizes, or if a view shrinks or expands.

As a consequence of mobile devices making up such a large part of internet search requests, search engines including Bing and Google place a high value on mobile-friendly interfaces for the sites they recommend. Modern HTML conventions for fluid design are a key part of that startegy. If the HTML is riddled with errors, the algorithms may not be able to tell if your website is mobile friendly, or not. It might even know exactly which devices won't work with your site.

Valid HTML is much more robust. Cleaning up the errors and warnings in your HTML markup is a key step in making your website anti-fragile, and improving the effectiveness of your content optimizations for keywords in search.

Fixing HTML Markup Simplifies Maintenance

Websites with correctly validating HTML are easier to maintain.

If it's easier to upate your website to add new content, features, sections or to update your HTML template to modern standards. Updates like this are noticed by the algorithms of Google, Microsoft, and other indexes. Periodic updates makes your site appears active and fresh to the indexing algorithms.

If it's difficult to update your site, it can look abandonned or stale. When it's easier to maintain your site, you're more likely to fix problems as you discover them, or take advantage of new opportunites.

There's bonus, too: if your website is easier to update, this facilitates occasional A/B testing, which can help you answer simple questions, such as, "should my call-to-action button be red, blue, or green?" If your website is difficult to maintain, A/B testing can be viewed as too time-consuming and expensive, and you're left guessing about what's most effective for your SEO and conversion of prospects and leads to subscribers and customers.

Easier maintence of web sites leads to better better websites and improved SEO performance.

Improved Accessiblity

People who rely on screen readers (such as the visually impaired) may find web pages difficult or impossible to navigate and read, if the site has even modest errors in the HTML markup.

HTML markup has been improved and extended in recent years as a result of such efforts as the W3C Web Accessibility Initiative (WAI). Errors in HTML markup undermine the accessibilty of your website.

Big platform companies like Apple, Google, and Microsoft have invested heavily in recent years to make both their platforms (iOS, Android, Windows) and the World Wide Web, more accessible. Their web browsers (Safari, Chrome, Edge) support WAI-ARIA and each company encourages web developers to support evolving accessibilty standards, as does Mozilla with the Firefox development community.

Google has telegraphed the importance of accessiblity and it's likely that their algorithms already understand how to evaluate the accessibilty of a site.

"Everyone should be able to access and enjoy the web. We’re committed to making that a reality."
Google Accessibility website

Another technology trend is contributing to the rapidly increasing importance of accessiblity and correct HTML markup:  voice platforms.

The rising popularity of first podcasts and then voice-search from mobile devices via Siri, Google Assistant, and Cortana, has brought industry attention to bear on voice. In recent years, the venture capital community has rapidly ramped up investment in voice, which was nearly triple in 2019 compared to the previous year, and has continued to rise.

Correct HTML markup is vital to make sure your website remains visible in search rankings as customers move to voice platforms.

Smarter Quality Assurance

Quality Assurance becomes more difficult and expensive because non-compliant HTML (such as divs inside h1 tags) may be undefined, and render differently in differnt browsers.

As with any programming platform, identifying and fixing HTML markup issues early and continuously in website development will be more effective and less expensive than ignoring the issues.

The less time your team spends stuggling to identify and fix weird issues that ultimately trace back to poorly maintained HTML markup, the more time they'll have to focus on the more important opportunities for search optimization.  

Better Web Apps

HTML templates that have errors are more difficult to use as front ends for dynamic web applications. Cleanly validating HTML makes for easier app UI integration, more efficient troubleshooting of customer issues, and a better user experience.

A key purpose of many modern SEO efforts is to create funnels which bring people into your app community, where you provide services they seek. Interfaces for web apps need correct HTML in order to provide the type of customer experince that can co-exist with high quality native apps.

If users bounce out once they're into the app due to a clunky user interface (UI) and poor user experience (UX) then the most successful SEO efforts would be wasted. Valid HTML helps app performance and user retention, and allows you to capture the value from your SEO efforts.

Image shows a typical mock-up for a mobile app, with a smartphone and placeholder text
Valid HTML Markup for Web Apps is Essential for SEO Performance

Vendor-Supplied HTML Templates

If you're using one or more HTML templates in your web development, or if you're a vendor of templates to the public or within your enterprise, this principle is important for you, too — possibly even more important. HTML templates can be force-multipliers. Errors in templates can be propagated to hundred or thousands of web pages, making problems even more difficult to correct.

Cleanly validating HTML markup can be even more important for commercial HTML template vendors. Errors in an HTML template make it more difficult to maintain (it's harder for webmasters, web designers, and app developers to upgrade their applications or websites to a new version of the template when it becomes available).

If an HTML template is well structured and error-free, it may lead to a great many more websites with valid HTML. Templates with errors however, can undermine the SEO efforts of many unsuspecting web design teams.

Valid HTML Markup is the Foundation for More Effective SEO

Google (and other web spiders) may strugle to understand page structure. SEO is undermined by validation errors. Google in particular encourages cleanly validating web pages and is believed to demote pages with invalid HTML.

If you lead a web design team or create templates for others to use, please join SEOtipster and adopt this principle for robust website development and effective SEO:  HTML markup should be valid and free of errors and warnings.

SEOtipster TODO:

  • This blog is hosted on Ghost. In a slight irony, at the time of publishing there were a handful of markup validation errors in the Ghost-emitted HTML. I should report these issues to Ghost, and persuade the Ghost team to commit to making markup validation part of their standard development process.