HTML Checking for Large Sites
Rocket Validator integrates the W3C Validator HTML checker into an automated web crawler.
The attributes width and height of <iframe> elements expect a non-negative integer, so an empty string is not allowed. Either define the correct dimension, or remove this attribute.
Learn more:
Related W3C validator issues
The attributes width and height of <img> elements expect a non-negative integer, so an empty string is not allowed. Either define the correct dimension, or remove this attribute.
The width and height attributes on <img> elements expect a digit to specify the dimension in pixels. It should not contain units, letters or percent signs.
You can achieve this using CSS instead, for example:
<!-- Invalid syntax, the height attribute expects only digits -->
<img src="photo.jpg" alt="cat" height="auto" />
<!-- Valid syntax using CSS -->
<img src="photo.jpg" alt="cat" style="height: auto" />The <iframe> element, used to embed another document inside the current document, accepts both attributes width and height which must be valid non-negative integers. Percentages are not allowed for these attributes.
The attributes width and height on <img> elements define the dimensions of the image in CSS pixels, and expect a non-negative integer.
Still checking your large sites one page at a time?
Save time using our automated web checker. Let our crawler check your web pages on the W3C Validator.
The <iframe> element, used to embed another document inside the current document, accepts both attributes width and height which must be valid non-negative integers. Percentages are not allowed for these attributes.
The width and height attributes on <img> and <iframe> elements expect a digit to indicate the number of pixels. Ensure that this attribute contains only digits.
For example:
<!-- This is invalid because width is not a digit -->
<img width="225px" height="100px" alt="cat" src="cat.jpg" />
<!-- This is valid -->
<img width="225" height="100" alt="cat" src="cat.jpg" />6,250 HTML checks per week. Fully automated.
Save time using our automated web checker. Let our crawler check your web pages on the W3C Validator.
The <table> element does not accept a height attribute. Use CSS instead.
The seamless attribute was proposed to be included in the HTML5 spec, but it wasn’t finally accepted, so it’s not a valid attribute for <iframe>.
There is an iframe tag inside a noscript tag that is itself inside the head section of the HTML document. This is not allowed because an iframe cannot be nested inside the head section.
To fix this issue, you may move the noscript section that contains the iframe tag outside of the head section, and ensure that it is placed within the body section of the HTML document.
For example, this is invalid HTML because the head section cannot contain iframe elements:
<!DOCTYPE html>
<html lang="en">
<head>
<title>My webpage</title>
<noscript>
<p>Please enable JavaScript to view this website</p>
<iframe src="https://example.com/"></iframe>
</noscript>
<!-- Other meta tags and styles go here -->
</head>
<body>
<!-- Rest of your webpage content goes here -->
</body>
</html>Moving the noscript inside the body section fixes the issue, as that’s where iframe elements belong:
<!DOCTYPE html>
<html lang="en">
<head>
<title>My webpage</title>
<!-- Other meta tags and styles go here -->
</head>
<body>
<noscript>
<p>Please enable JavaScript to view this website</p>
<iframe src="https://example.com/"></iframe>
</noscript>
<!-- Rest of your webpage content goes here -->
</body>
</html>IDs for HTML elements can’t be blank.
When was the last time you validated your whole site?
Keep your sites healthy checking for A11Y/HTML issues on an automated schedule.