2023: 0 of the Global Top 100 Websites Use Valid HTML · Jens Oliver Meiert

Created on November 12, 2023 at 11:04 am

2023 DATE : 0 CARDINAL of the Global Top 100 Websites Use Valid HTML

Let’s dive right in: Nothing changed compared to last year DATE —none of the 100 CARDINAL most-visited websites globally uses HTML in full conformance with the HTML specification.

The following data gives an impression of precision that is greater than warranted. The point of this annual DATE analysis is to check on full HTML conformance (absence of markup errors); that is, CSS conformance checks are a bonus, and the specific error counts don’t matter for the purpose of telling conformance or non-conformance, either. I’m providing the data for further study, and for comparability to previous years DATE .


After 2021 and 2022 DATE , I used the annual DATE update of the Ahrefs ORG Top 100 CARDINAL websites to check the homepages of these websites on HTML conformance.

For that purpose I took all the respective URLs, prepared HTML and CSS validation URLs, and documented the error counts of the 200 CARDINAL tests in a spreadsheet:

Figure: The most-frequented websites and their use of HTML and CSS ORG according to the specifications.

HTML Conformance in 2023 DATE

0 of the 100 CARDINAL websites have 0 CARDINAL HTML conformance errors.

3 CARDINAL ( Adobe ORG , Speedtest ORG , and Spotify ORG ) were very close to conformance, with 1 CARDINAL error each. 14 CARDINAL more had a single-digit number of issues.

37 CARDINAL were far away from conformance with any specification ( 100 CARDINAL or more errors).

The average number of HTML ORG errors is 132.14 CARDINAL .

The HTML errors median is 62 DATE .

(The mode is 23 CARDINAL .)

CSS Conformance in 2023 DATE

The W3C CSS validator needs updating. There appear to be many false positives (and a suspicion of false negatives), raising concern that the results aren’t practically useful anymore (perhaps not even for ballpark numbers). CSS conformance isn’t as critical as HTML conformance, but it’s important for us to have a reliable CSS validator.

12 CARDINAL of 94 CARDINAL tested websites have 0 CSS conformance errors. ( 6 CARDINAL websites could not be checked.)

34 CARDINAL were close to conformance, with a single-digit number of errors.

7 CARDINAL were far away ( 100 CARDINAL or more errors, with one CARDINAL site containing more than 1,000 CARDINAL errors).

The average number of CSS ORG errors is 46.79 CARDINAL .

The median is 10.5 CARDINAL .

(The mode is 0 CARDINAL .)

HTML and CSS Conformance over Time

We need to test more websites to make this significant, but given that this has been the third ORDINAL analysis, here is how error counts developed over the years DATE :

2021 2022 DATE 2023 HTML ø 125.22 CARDINAL errors ø 125.63 CARDINAL errors → ø 132.14 DATE errors ↗ 2 CARDINAL homepages without errors 0 CARDINAL homepages without errors ↘ 0 CARDINAL homepages without errors → CSS ø 48.40 LAW errors ø 26.33 CARDINAL errors ↓ ø 46.79 CARDINAL errors ↑ 3 CARDINAL homepages without errors 13 CARDINAL homepages without errors ↑ 12 CARDINAL homepages without errors →


I think the results speak for themselves.

Personally, I’m outspoken about the usefulness of conformance—I think it’s foundational for our field, that it should be a hiring criterion, and that it could unite us to tackle other important challenges. (If you’re interested, I also run an ebook series—check out the latest edition—explaining and promoting valid, minimal HTML.)

While that’s me, even during the years DATE of the Web Standards Project ORG ( 1998–2013 DATE ), our field has neither accepted this nor any other quality standard for its output.

We can use every developer to improve this—lead by example and ship valid code—, but going by the data, there’s no change in sight.

About Me

I’m Jens PERSON , and I’m an engineering lead and author. I’ve worked as a technical lead for companies like Google ORG , I’m close to W3C and WHATWG PERSON , and I write and review books for O’Reilly ORG and Frontend Dogma ORG . I love trying things, not only in web development, but also in other areas like philosophy. Here on meiert.com I share some of my views and experiences.

If you have a question or suggestion about what I write, please leave a comment (if available) or a message. Thank you!

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