Nearly 90% of top websites fail HTML standards — a growing problem in the AI age

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The ValidateHTML project examined the 5,000 most popular domains based on the Tranco list

Project lead Théo Ducreux found that just 53% of these sites had human-readable home pages

Almost 90% of the sites failed to meet W3C web standard, even serving violations of the HTML5 specification

ValidateHTML—an independent project overseen by French developer Théo Ducreux—has uncovered a flagrant disregard for web standards across most of the web’s most widely visited websites.

Examining 5,000 domains, ValidateHTML found that a little over half of the sites had human-readable home pages and failed to meet HTML standards set out by the World Wide Web Consortium (W3C) and the WHATWG (Web Hypertext Application Technology Working Group).

The websites were selected from the Tranco list of the top 5,000 websites, and Ducreux’s research has highlighted a disappointing trend of websites being published because they’re “good enough” with modern browsers capable of fixing the majority of coding errors they encounter.

ValidateHTML finds invalid HTML

Théo Ducreux’s project involved submitting each of the 5,000 websites to the HTML5 validation tool at html-validate.org . Only homepages were checked; no checkouts or CMS-generated articles were included, which Decreux judges to be “almost certainly worse.”

Announcing the findings of ValidateHTML, Ducreux decisively stated that “valid HTML is the exception, not the rule.” An incredible 87.2% of the web’s most visited sites have HTML violations on their home page, with just 12.8% offering “fully valid HTML.” But this is a generous approach; if the best practices for web standards are applied, then only 2.6% of Tranco’s top 5,000 sites can be stated to have valid HTML.

Meanwhile, accessibility issues are present on over 33% of sites. European Accessibility Act and similar rules around the world mean that compliance is being rejected. That’s potentially pretty risky, as it can result in fines.

Ducreux also ran the validatehtml.com domain through the same validation tool, which highlighted some errors.

Why are web standards important?

The standards established by the W3C since 1996 and the WHATWG (which includes Apple, Google, Mozilla, and Microsoft) since 2004 have ensured website developers put people first, ensuring people with accessibility challenges can consume content, and preventing unreasonable or secret code and designs.

It could be argued that in an age of AI-based website-reading bots, web standards are no longer relevant, but this ignores a couple of key facts. Firstly, the standards are important for ensuring websites are readable across all browsers.

Secondly, and arguably more important to the point, is that AI bots actually like human-readable material. It signifies that the site in question is intended for people to read and/or use and is therefore worth visiting.

Coders producing websites that fail to meet web standards aren’t only giving themselves a problem that needs fixing later. Clients or managers might look elsewhere for a solution, potentially considering AI-generated code as an alternative.