HTML Guide

The src attribute on an <img> element contains an invalid character, that should be properly encoded as a URI percent-encoded character.

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 for <img> tags is required, to define the source of the image, like in this example:

<img src="photo.jpg" alt="wombat" />

The src attribute contains square brackets ([ or ]) in the URL’s query string, which are not permitted in valid HTML URLs.

According to the HTML standard, attribute values such as URLs must conform to valid URI syntax. Unencoded square brackets are reserved characters in URI syntax and must be percent-encoded. Specifically, [ should be replaced with %5B and ] with %5D. This ensures the URL is correctly interpreted by browsers and validators. For example, a URL parameter like sort=[asc] should be coded as sort=%5Basc%5D.

Correct HTML Example:

<iframe src="/page?time=%5Btimestamp%5D"></iframe>

Always encode reserved characters in URLs when using them in HTML attribute values to ensure W3C compliance.

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.

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.

To fix the issue of having a bad value for the src attribute on an img element due to having a tab, new line, or carriage return, you need to ensure that the src attribute does not contain any additional whitespace characters like tab, new line, or carriage return.

Incorrect code:

<img src="images/example.jpg
" alt="Example Image">

Corrected code:

<img src="images/example.jpg" alt="Example Image">

By removing the extra whitespace characters (new line in this case) and ensuring that the src attribute value is properly enclosed within quotes, the issue should be resolved.

The issue arises from the space character in the src attribute value of the script element. In URLs, spaces are not allowed and should be properly encoded to avoid validation errors.

Fix

Replace spaces with %20, which is the URL-encoded representation of a space.

Example

Before:

<script src="https://example.com/media assets/app.js"></script>

After:

<script src="https://example.com/media%20assets/app.js"></script>

Explanation

In this example, the space between “media” and “assets” in the URL is replaced with %20. This change ensures that the URL conforms to standards and is correctly processed by browsers and servers. Spaces and other special characters in URLs must be encoded to ensure proper formatting and accessibility.

<img> tags used to display images require the attribute src to indicate the source of the image, for example <img src="/img/photo.jpg" />.