HTML Guide
An empty src attribute on a source element is invalid; it must contain a valid non-empty URL.
The source element is typically used within audio or video elements to specify multiple media source files. The src attribute defines the path to the media file, and it must not be empty, as per the HTML standard.
Incorrect Example:
<video controls>
<source src="" type="video/mp4">
Your browser does not support the video tag.
</video>Corrected Example:
<video controls>
<source src="movie.mp4" type="video/mp4">
Your browser does not support the video tag.
</video>
Always ensure the src attribute on source is present and contains a valid, non-empty URL.
Learn more:
Related W3C validator issues
An <iframe> element allows to embed an HTML document inside another HTML document, and its src attribute is indicated the source URL of the embedded web page. The src attribute is a required attribute, so it cannot be blank.
Example:
<iframe src="https://example.com/map.html"></iframe>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 <script> tag allows authors to include dynamic scripts and data blocks in their documents. When the src is present, this tag accepts a type attribute which must be either:
- an empty string
- text/javascript (that’s the default, so it can be omitted)
- module
Examples:
<!-- This is valid, without a type it defaults to JavaScript -->
<script src="app.js"></script>
<!-- This is valid, but will warn that it can be omitted -->
<script type="text/javascript" src="app.js"></script>
<!-- An empty attribute is valid, but will warn that it can be omitted -->
<script type="" src="app.js"></script>
<!-- The module keyword is also valid as a type -->
<script type="module" src="app.js"></script>
<!-- Any other type is invalid -->
<script type="wrong" src="app.js"></script>
<script type="text/html" src="app.js"></script>
<script type="image/jpeg" src="app.js"></script>The href attribute on the link element must not be empty.
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 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.
An <iframe> element allows to embed an HTML document inside another HTML document, and its src attribute is indicated the source URL of the embedded web page. The query part of that URL contains one or more space characters, which are not allowed, for example:
<iframe src="https://maps.google.it/maps?q=2700 6th Avenue"></iframe>You should properly escape all space characters as %20 like this:
<iframe src="https://maps.google.it/maps?q=2700%206th%20Avenue"></iframe>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 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">