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

About This HTML Issue

When a browser loads an HTML document, it needs to know which character encoding to use to correctly interpret the bytes in the file. The <meta> tag’s charset attribute (or the http-equiv="Content-Type" declaration) tells the browser what encoding to expect. If this declaration says windows-1251 but the file is actually saved as utf-8, the browser faces conflicting signals — the declared encoding disagrees with the actual byte content.

This mismatch matters for several reasons:

Broken text rendering: Characters outside the basic ASCII range (such as accented letters, Cyrillic, CJK characters, emoji, and special symbols) may display as garbled or replacement characters (often seen as Ð sequences, �, or other mojibake).
Data integrity: Form submissions and JavaScript string operations may produce corrupted data if the browser interprets the encoding incorrectly.
Standards compliance: The WHATWG HTML Living Standard requires that the encoding declaration match the actual encoding of the document. Validators flag this mismatch as an error.
Inconsistent behavior: Different browsers may handle the conflict differently — some may trust the <meta> tag, others may sniff the actual encoding — leading to unpredictable results across user agents.

How to fix it

Determine the actual encoding of your file. Most modern text editors (VS Code, Sublime Text, Notepad++) display the file encoding in the status bar. If your file is saved as UTF-8 (which is the recommended encoding for all new web content), your <meta> tag must reflect that.
Update the <meta> tag to declare utf-8 instead of windows-1251.
Prefer the shorter charset syntax introduced in HTML5, which is simpler and equivalent to the older http-equiv form.
Place the encoding declaration within the first 1024 bytes of the document, ideally as the first element inside <head>, so the browser encounters it before parsing other content.

Examples

❌ Incorrect: declared encoding doesn’t match actual file encoding

The file is saved as UTF-8 but the <meta> tag declares windows-1251:

<head>
  <meta charset="windows-1251">
  <title>My Page</title>
</head>

Or using the older http-equiv syntax:

<head>
  <meta http-equiv="Content-Type" content="text/html; charset=windows-1251">
  <title>My Page</title>
</head>

✅ Correct: declared encoding matches the actual UTF-8 file

Using the modern HTML5 charset attribute:

<head>
  <meta charset="utf-8">
  <title>My Page</title>
</head>

Or using the equivalent http-equiv form:

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

✅ Correct: full document example

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <title>My Page</title>
  </head>
  <body>
    <p>Hello, world!</p>
  </body>
</html>

What if you actually need `windows-1251`?

If your content genuinely requires windows-1251 encoding (for example, a legacy Cyrillic text file), you need to re-save the file in windows-1251 encoding using your text editor. However, UTF-8 is strongly recommended for all web content because it supports every Unicode character and is the default encoding for HTML5. Converting your file to UTF-8 and updating the <meta> tag accordingly is almost always the better path forward.

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Learn more:

MDN Reference

Character encoding declaration

→

WHATWG Spec

Character sets & encodings

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