HTML Guide
This error message indicates that there is a backslash (\) used in a URL, which is not a valid character for URL paths.
You’ll need to replace the backslashes with forward slashes (/) in the URL path segments.
Here’s an example of a correct img tag using a valid URL path:
<img src="https://example.com/img/small/photo.png" alt="example image">Also, make sure that the URL is correct and that the image file actually exists in the specified location.
Related W3C validator issues
The src attribute on an <img> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.
The href attribute of the a element contains an invalid backslash character, which is not permitted in URLs.
According to the WHATWG HTML living standard, the href attribute must contain a valid URL. URLs use forward slashes (/) for path separators, and backslashes are not allowed as they can cause browsers and validators to misinterpret the address. Backslashes often arise when file paths are copied from Windows environments.
Correct Usage:
- Always use forward slashes / in your URLs.
- Remove any backslashes from href values.
Example of incorrect usage:
<a href="images\picture.jpg">View Picture</a>Corrected example:
<a href="images/picture.jpg">View Picture</a>The src attribute for <img> tags is required, to define the source of the image, like in this example:
<img src="photo.jpg" alt="wombat" />Ensure the src attribute on the script element is non-empty and points to a valid resource.
The src attribute in a script element specifies the URL of an external script file. An empty src attribute is invalid because it tells the browser to fetch a resource from a URL that is not provided, leading to loading errors. Instead, ensure that the src attribute contains a valid file path or URL to an existing script file. If the script content is meant to be inline, you should omit the src attribute altogether and include the script content directly within the script element.
Example of a Valid External Script
Here is a valid example of a script element with a non-empty src attribute:
<!DOCTYPE html>
<html lang="en">
<head>
<title>Valid Script Example</title>
</head>
<body>
<script src="path/to/script.js"></script>
</body>
</html>Example of a Valid Inline Script
If the script is to be written inline, exclude the src attribute and write the JavaScript code directly within the script tags:
<!DOCTYPE html>
<html lang="en">
<head>
<title>Inline Script Example</title>
</head>
<body>
<script>
console.log('This is an inline script.');
</script>
</body>
</html>Troubleshooting
Double-check the script’s file path:
- Ensure the file path you provide in the src is correct relative to the HTML file.
- Make sure the script file exists in the location specified.
- If using a network URL, verify that the URL is correct and accessible.
The sizes attribute for an img element requires valid CSS syntax, and auto is not an acceptable value within that attribute.
The sizes attribute allows you to specify a list of media conditions and corresponding sizes for the images. Each condition determines which size of the image should be displayed at different viewport widths, ensuring responsive image delivery. The syntax for sizes should be a comma-separated list of media queries followed by a value denoting the corresponding width of the image. This width value may be in pixels (px) or as a percentage (vw, vh), but auto is not valid in this context.
Here is a breakdown of a correct sizes attribute usage:
- 50vw: This denotes that the image should take up 50% of the viewport’s width.
- (max-width: 600px) 100vw, 50vw: When the viewport is at most 600 pixels wide, the image should occupy the full width (100vw). Otherwise, it should take 50 percent of the viewport width.
Remove “auto” from your sizes value and provide a valid, contextually correct CSS value.
Example
<!DOCTYPE html>
<html lang="en">
<head>
<title>Responsive Images Example</title>
</head>
<body>
<img
src="image.jpg"
sizes="(max-width: 472px) 100vw, 472px"
srcset="image-small.jpg 300w, image-medium.jpg 600w, image-large.jpg 1000w"
alt="A description of the image"
>
</body>
</html>In this example, if the viewport width is less than or equal to 472 pixels, the image will take up the entire width (100vw). For larger widths, the srcset specifies different image files for varying resolutions.
The sizes attribute on the img element must use CSS length units (such as px, vw, em) and not image width descriptors like w.
The sizes attribute defines the intended display size of the image in CSS length units, which helps the browser select the appropriate image from the srcset. Use units like px (pixels) or vw (viewport width percentage), not w, which is used in the srcset descriptors. The srcset attribute specifies different image resources and their width descriptors (e.g., 860w), while sizes reflects the image’s display size in the layout.
Correct usage:
- sizes="(min-width: 568px) 140px" tells the browser the image will be displayed as 140 pixels wide when the viewport is at least 568 pixels wide.
- srcset="photo.png?w=860&q=90 860w" uses w as the descriptor for the image resource’s width.
HTML example:
<img
alt=""
sizes="(min-width: 568px) 140px"
srcset="photo.png?w=860&q=90 860w"
src="photo.png?w=860&q=90">Summary:
- Use CSS units like px, vw, etc. in the sizes attribute.
- Use the w descriptor only in srcset, not in sizes.
The src attribute on an element <img> contains a character which is not allowed unless properly encoded.
Special characters needing encoding are: :, /, ?, #, [, ], @, !, $, &, ', (, ), *, +, ,, ;, =, as well as % itself.
For example, this image tag is incorrect because the src attribute contains an the unallowed characters [ and ]:
<img src="image[00].svg" alt="logo">Instead, this is the properly percent-encoded src attribute, where [ has been replaced with %5B and ] with %5D.
<img src="image%5B00%5D.svg" alt="logo">Space characters are not allowed in src attributes. Instead, they should be converted to %20. In this example, the first line is invalid and the second is valid:
<img src="https://example.com/?s=some term" alt="description" />
<img src="https://example.com/?s=some%20term" alt="description" />The src attribute on an element <img> contains a character that is not allowed, and should be encoded.
Some typical examples include the pipe character | that should be replaced by its encoded alternative %7C , and the left square bracket [ that needs to be encoded as %5B.
The src attribute on an <img> tag is not allowed to contain space characters. You should replace them with “%20“.