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Charset declaration is missing or occurs too late in the HTML

Servers and browsers communicate with each other by sending bytes of data over the internet. If the server doesn't specify which character encoding format it's using when it sends an HTML file, the browser won't know what character each byte represents. The character encoding declaration specification solves this problem.

Theoretically, a late <meta charset> element (one that is not fully contained in the first 1024 bytes of the document) can also significantly affect load performance. See Issue #10023.

How the Lighthouse charset audit fails

Lighthouse flags pages that do not specify their character encoding:

The failing character encoding audit.

Lighthouse considers the character encoding to be declared if it finds any of the following:

  • A <meta charset> element in the <head> of the document that is completely contained in the first 1024 bytes of the document
  • A Content-Type HTTP response header with a charset directive that matches a valid IANA name
  • A byte-order mark (BOM)

Each Best Practices audit is weighted equally in the Lighthouse Best Practices Score. Learn more in The Best Practices score.

How to pass the charset audit

Add a <meta chartset> element to your HTML

Add a <meta charset> element within the first 1024 bytes of your HTML document. The element must be fully contained within the first 1024 bytes. The best practice is to make the <meta charset> element the first element in the <head> of your document.

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">

Add a Content-Type HTTP response header

Configure your server to add a Content-Type HTTP response header that includes a charset directive.

Content-Type: text/html; charset=UTF-8

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