The only allowed value for the “accept-charset” attribute for the “form” element is “utf-8”.

The accept-charset attribute on a <form> element only accepts "UTF-8" as its value. Any other character encoding will trigger a validation error.

Older HTML specifications allowed values like "ISO-8859-1", "Windows-1252", or space-separated lists of encodings. The HTML living standard changed this. Now, "UTF-8" is the sole permitted value. Browsers already default to submitting form data in UTF-8 when no accept-charset is specified, so the attribute is rarely needed at all.

If a form currently specifies a non-UTF-8 encoding, the fix is either to switch the value to "UTF-8" or to remove the attribute entirely. Removing it is usually the better choice, since the browser will use UTF-8 by default when the page itself is served as UTF-8 (which it should be).

HTML examples

Invalid usage

<form action="/search" accept-charset="ISO-8859-1">
  <input type="text" name="q">
  <button type="submit">Search</button>
</form>

Valid usage

Remove the attribute and let the browser default to UTF-8:

<form action="/search">
  <input type="text" name="q">
  <button type="submit">Search</button>
</form>

Or explicitly set it to "UTF-8":

<form action="/search" accept-charset="UTF-8">
  <input type="text" name="q">
  <button type="submit">Search</button>
</form>

Learn more:

MDN Reference

HTML form element - MDN

→

WHATWG Spec

HTML forms - WHATWG

→

web.dev Article

HTML forms - web.dev

→