About This HTML Issue
The http-equiv attribute on the <meta> element is designed to simulate certain HTTP response headers directly in HTML. However, the HTML specification only permits a specific set of values: content-type, default-style, refresh, x-ua-compatible, and content-security-policy. Using Expires as a value for http-equiv will trigger a validation error because it falls outside this permitted set.
Historically, some older browsers and HTML versions were more lenient about which values could appear in http-equiv, and developers commonly used <meta http-equiv="Expires" content="0"> or similar patterns to try to prevent page caching. However, this approach was never reliable — browsers and caching proxies handle actual HTTP headers far more consistently than <meta> tag equivalents. Modern HTML formally disallows this value.
Beyond standards compliance, there are practical reasons to avoid this pattern. Many browsers simply ignore unrecognized http-equiv values, meaning the tag does nothing useful. Cache behavior is best controlled at the HTTP level, where servers, CDNs, and proxies all read and respect the headers. Relying on a <meta> tag for caching gives a false sense of control while cluttering your markup with invalid code.
To fix this issue, remove the <meta http-equiv="Expires" ...> tag from your HTML and configure the Expires or Cache-Control HTTP header on your web server.
Examples
Incorrect: Using Expires in http-equiv
This triggers the validation error:
<head>
<meta charset="UTF-8">
<meta http-equiv="Expires" content="0">
<meta http-equiv="Expires" content="Tue, 01 Jan 2025 00:00:00 GMT">
<title>My Page</title>
</head>
Correct: Remove the invalid <meta> tag
Simply remove the offending tag. Only use valid http-equiv values:
<head>
<meta charset="UTF-8">
<title>My Page</title>
</head>
Correct: Valid uses of http-equiv
For reference, here are examples of valid http-equiv values:
<head>
<meta charset="UTF-8">
<meta http-equiv="refresh" content="30">
<meta http-equiv="content-security-policy" content="default-src 'self'">
<meta http-equiv="default-style" content="main-stylesheet">
<title>My Page</title>
</head>Correct: Set cache expiration via server configuration
The proper way to control caching is through HTTP response headers configured on your server.
Apache (.htaccess or server config):
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType text/html "access plus 1 day"
</IfModule>
Or using Cache-Control with mod_headers:
<IfModule mod_headers.c>
Header set Cache-Control "no-cache, no-store, must-revalidate"
Header set Expires "0"
</IfModule>Nginx:
location ~* \.html$ {
expires 1d;
add_header Cache-Control "public, no-transform";
}To prevent caching entirely in Nginx:
location ~* \.html$ {
expires -1;
add_header Cache-Control "no-store, no-cache, must-revalidate";
}If you don’t have access to server configuration, many server-side languages let you set headers programmatically. For example, in PHP:
<?php
header("Expires: Tue, 01 Jan 2030 00:00:00 GMT");
header("Cache-Control: public, max-age=86400");
?>By handling cache expiration at the server level, you get reliable behavior across all browsers, proxies, and CDNs — while keeping your HTML clean and standards-compliant.
Find issues like this automatically
Rocket Validator scans thousands of pages in seconds, detecting HTML issues across your entire site.