HTML Validation

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

About This HTML Issue

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>

Learn more:

→ HTML Living Standard: src attribute on iframe

Last reviewed: October 27, 2022

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Related W3C Validator Issues (38)

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 “script”: Must be non-empty.

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.

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

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.

Bad value X for attribute “src” on element “iframe”: Illegal character in fragment: “#” is not allowed.

The URL in the src attribute value for an iframe is invalid as it contains an unexpected hash (#) character.

There’s an unexpected, possibly duplicate, hash character in the URÑ.

Examples:

Incorrect:

<iframe src="https://example.com/#?secret=123#abc"></iframe>

Correct (using only the query string):

<iframe src="https://example.com/#?secret=123"></iframe>

Correct (using the query string and a hash fragment) :

<iframe src="https://example.com/?secret=123#abc"></iframe>

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

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.

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

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>

A “script” element with a “src” attribute must not have a “type” attribute whose value is anything other than the empty string, a JavaScript MIME type, or “module”.

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>

Attribute “seamless” not allowed on element “iframe” at this point.

Bad start tag in “iframe” in “noscript” in “head”.

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>

Bad value “allow-storage-access-by-user-activation” for attribute “sandbox” on element “iframe”: The string “allow-storage-access-by-user-activation” is not a valid keyword.

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