HTML Validation

Bad value “” for attribute “src” on element “source”: Must be non-empty.

About This HTML Issue

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:

Last reviewed: August 04, 2025

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Reading time

1 min read

Category

HTML Validation

Engine

W3C Validator

Last reviewed

August 04, 2025

Resources

Related W3C Validator Issues

Bad value “x” for attribute “src” on element “img”: Tab, new line or carriage return found.

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.

Bad value X for attribute “src” on element “script”: Illegal character in path segment: space is not allowed.

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.

Bad value for attribute “src” on element “iframe”: Illegal character in query: “[” is not allowed.

Illegal character “[” in the iframe src URL requires percent-encoding or removal.

The iframe element’s src must be a valid URL. According to URL syntax, characters like [ and ] are not allowed in the query unless percent-encoded. If your src contains array-like parameters (e.g., filters[category]=news), encode reserved characters: [ becomes %5B and ] becomes %5D. Avoid spaces and encode other reserved characters as needed. Alternatively, adjust the server to accept dot or bracketless notation (e.g., filters.category=news or filters_category=news) so the URL stays valid without encoding.

HTML Examples

Example causing the validator error

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Iframe URL Error</title>
</head>
<body>
<!-- [ and ] are illegal in URLs unless encoded -->

  <iframe src="https://example.com/embed?filters[category]=news&filters[tags]=web"></iframe>
</body>
</html>

Fixed example with percent-encoding

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Iframe URL Fixed</title>
</head>
<body>
<!-- Encode [ as %5B and ] as %5D -->

  <iframe src="https://example.com/embed?filters%5Bcategory%5D=news&filters%5Btags%5D=web"></iframe>
</body>
</html>

Bad value for attribute “src” on element “img”: Fragment is not allowed for data: URIs according to RFC 2397.

Bad value for attribute “src” on element “img”: Illegal character in scheme data: “<” is not allowed.

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