HTML Validation

Internal encoding declaration “windows-1251” disagrees with the actual encoding of the document (“utf-8”).

About This HTML Issue

The document has been declared to use a windows-1251 charset but the actual contents seems to be utf-8. You should update the charset to that like in this example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

Last reviewed: October 27, 2022

Was this guide helpful?

Find issues like this automatically

Rocket Validator scans thousands of pages in seconds, detecting HTML issues across your entire site.

Start Free Trial See Pricing

Related W3C Validator Issues (36)

Bad value “text/html; charset=windows-1251” for attribute “content” on element “meta”: “charset=” must be followed by “utf-8”.

A <meta> tag has been found in the document stating that the charset is windows-1251, but it actually is utf-8. You should update the tag to reflect the actual encoding of the document, for example:

<meta http-equiv="Content-Type" content="text/html; charset=utf-8">

Forbidden code point X

Internal encoding declaration “utf-8” disagrees with the actual encoding of the document (“windows-1252”).

The character encoding declared in the HTML differs from the actual file encoding.

The meta element with charset="utf-8" tells browsers to interpret the document as UTF-8. However, if the file is actually saved in another encoding (such as Windows-1252), validators and browsers will detect a mismatch, leading to this error. To resolve this, you must ensure the file contents and the encoding declaration match.

Recommended: Save your document in UTF-8 encoding to match your meta tag.
Alternatively, if you must use Windows-1252, update charset accordingly.

UTF-8 example (preferred):

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>UTF-8 Encoding Example</title>
    <meta charset="utf-8">
  </head>
  <body>
    <p>This page is encoded in UTF-8.</p>
  </body>
</html>

Windows-1252 example (not recommended):

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Windows-1252 Encoding Example</title>
    <meta charset="windows-1252">
  </head>
  <body>
    <p>This page is encoded in Windows-1252.</p>
  </body>
</html>

Summary:

Use UTF-8 as your file encoding and declare <meta charset="utf-8">.
Always make sure the file is saved using the same encoding you declare in the HTML.

A document must not include both a “meta” element with an “http-equiv” attribute whose value is “content-type”, and a “meta” element with a “charset” attribute.

In order to define the charset encoding of an HTML document, both of these options are valid, but only one of them must appear in the document:

<!-- This is the preferred way -->

<meta charset="UTF-8">

<!-- This is the older way, also valid -->

<meta http-equiv="content-type" content="text/html; charset=UTF-8">

Bad value for attribute “action” on element “form”: Percentage ("%") is not followed by two hexadecimal digits.

The issue here is related to the encoding of URLs. In HTML and URLs, special characters that have specific meanings need to be encoded to ensure that the URL is interpreted correctly. This process converts characters to their percent-encoded form, where a character is replaced by % followed by two hexadecimal digits representing the ASCII code of the character.

Explanation:

The action attribute of a <form> element specifies where to send the form-data when a form is submitted.
If the URL contains special characters (e.g., spaces, <, >, #, %, etc.), they need to be percent-encoded. For instance, a space character is encoded as %20.
In this case, the validator is complaining about a % sign that is not correctly followed by two hexadecimal digits, which typically happens if the URL was not properly encoded.

How to Fix:

Check the URL: Look for any raw special characters that need encoding.
Correctly Encode the URL: Use online tools or libraries that provide URL encoding support to ensure that the URL is correctly percent-encoded.

Example:

Suppose you have the following incorrect form tag:

<form action="submit%data.html">
<!-- form elements here -->

</form>

The % in submit%data.html should be followed by two hexadecimal digits. If %data was intended to be a part of the URL, it should be encoded properly. Here is how to correct it:

<form action="submit%25data.html">
<!-- form elements here -->

</form>

If % should represent data, replace % with %25, which is the percent-encoded form of %. Always verify each special character is correctly encoded. Using this approach ensures that the URL in the action attribute is valid according to HTML standards.

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: “[” 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>

Bad value “X” for attribute “href” on element “link”: Illegal character in path segment: “X” is not allowed.

An illegal character has been found for the “href” attribute on the “link” element.

To fix this issue, find the “link” element in question and make sure that the “href” attribute contains a valid URL without any illegal characters.

Here’s some example HTML code of a link element:

<!DOCTYPE html>
<html>
  <head>
    <title>My Webpage</title>
    <link rel="stylesheet" href="styles/main.css">
  </head>
  <body>
    <h1>Welcome to my webpage!</h1>
    <p>Here is some content...</p>
  </body>
</html>

In the above example, the link element has a valid href attribute value of styles/main.css. Make sure that your href attribute values don’t contain any illegal characters.

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>

Ready to validate your sites?
Start your free trial today.

Pro Trial Free Trial