HTML Validation

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

About This HTML Issue

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.

Learn more:

→ MDN: Percent-encoding

Last reviewed: March 31, 2025

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Related W3C Validator Issues (107)

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”: Illegal character in scheme data: “<” is not allowed.

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 X for attribute “src” on element “script”: Illegal character in query: “"” is not allowed.

There is an illegal double quote character (") at the end of the src attribute value in your <script> tag, which causes the attribute to be invalid.

Attribute values must not include unescaped or stray quote characters (" or ') inside them, as this breaks attribute parsing and results in invalid HTML. The src attribute for a <script> tag should contain a properly encoded URL without any stray quotes or illegal characters. In your case, a double quote has accidentally been included before the closing quote of the attribute.

Correct usage for a <script> tag with the async attribute is:

<script src="https://example.com/js/jquery-3.6.0.min.js?ver=6.8.2" async></script>

Incorrect example with the error (shows the issue):

<script src="https://example.com/js/jquery-3.6.0.min.js?ver=6.8.2" async""></script>

Make sure there are no stray characters in your attribute values and that boolean attributes like async do not have values—it should simply be present, as in async, not async"" or async="async".

If you need a full, minimal HTML document to validate, use:

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Valid Script Tag Example</title>
  </head>
  <body>
    <script src="https://example.com/js/jquery-3.6.0.min.js?ver=6.8.2" async></script>
  </body>
</html>

Double-check your HTML source code to ensure there are no accidental typos or misplaced quote marks in your tag attributes.

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>

Bad value for attribute “href” on element “a”: Illegal character in fragment: space is not allowed.

Spaces in the URL fragment are invalid; encode them or remove them (e.g., use %20 or hyphens/underscores).

The href attribute must contain a valid URL. When using a fragment identifier (the part after #), it must follow URL syntax rules: no unescaped spaces. Fragments usually reference an element’s id. An element’s id must be unique and is case-sensitive; while spaces aren’t allowed in id values, many authors accidentally mirror text with spaces in the fragment. Use hyphens or underscores in ids and match the fragment, or percent-encode reserved characters. Prefer readable, dash-separated ids for accessibility and shareable links.

For example, instead of href=”#My Section”, use href=”#my-section” and set id=”my-section” on the target. If you must preserve spaces in a generated URL, encode them as %20, but it’s better to avoid spaces entirely in ids.

HTML Examples

Invalid: reproduces the validator error

<!doctype html>
<html lang="en">
  <head>
    <title>Fragment with space</title>
  </head>
  <body>
    <a href="#My Section">Go to section</a>

    <h2 id="My Section">My Section</h2>
  </body>
</html>

Fixed: use a valid fragment and id

<!doctype html>
<html lang="en">
  <head>
    <title>Valid fragment</title>
  </head>
  <body>
    <a href="#my-section">Go to section</a>

    <h2 id="my-section">My Section</h2>
  </body>
</html>

Alternatively, encoding the space also passes validation, though less ideal as the id would be invalid because it contains spaces:

<a href="#My%20Section">Go to section</a>
<h2 id="My Section">My Section</h2>

Bad value X for attribute “href” on element “a”: Illegal character in path segment

Bad value for attribute “href” on element “a”: Illegal character in query: space is not allowed.

Space characters are not permitted in the value of the href attribute; they must be properly percent-encoded.

The href attribute specifies a URL, and URLs must follow specific syntax rules defined by RFC 3986. Spaces and some other characters are considered illegal in URLs. To include a space in the URL, use the percent escape sequence %20 in place of the space character.

Incorrect example with an illegal space in the query string:

<a href="search.html?q=my search">Search for 'my search'</a>

Correct example using percent-encoding for the space:

<a href="search.html?q=my%20search">Search for 'my search'</a>

Replace all spaces in URLs within href attributes with %20 to ensure W3C validation and proper browser behavior.

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

Square brackets ([, ]) are not allowed unescaped in the query part of an href URL value.

The href attribute in the <a> element must contain a valid URL. According to the URL standard, certain characters, including square brackets, are not permitted directly in the query component unless percent-encoded. Using unescaped square brackets in the URL can cause validation errors and unexpected behavior in browsers.

To include a square bracket in the query string, use percent encoding:

[ encodes to %5B
] encodes to %5D

Incorrect usage:

<a href="search.html?q=[value]">Search</a>

Correct usage:

<a href="search.html?q=%5Bvalue%5D">Search</a>

This ensures the URL is valid and compliant with HTML standards.

Bad value for attribute “href” on element “a”: Illegal character in scheme data: “\” is not allowed.

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>

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