MIME-Version
The HTTP MIME-Version response header declares the
MIME protocol version used to construct the message. The
value is nearly always 1.0.
Usage
MIME-Version originates from email, where the header signals a MIME-compliant message body. In email, the header tells mail clients the message uses MIME encoding for attachments, character sets, and multipart structures.
HTTP adopted a different content negotiation model built around Content-Type, Content-Encoding, and Content-Length. These headers handle the same responsibilities MIME-Version serves in email, making the header redundant in HTTP responses. HTTP/1.1 does not require or define any behavior for MIME-Version.
Servers still send the header for several reasons. Web frameworks and application servers with email-adjacent roots (CGI scripts, multipart form handlers, document generation pipelines) often include MIME-Version automatically. Content management systems and enterprise platforms carry the header forward as a default. The header is harmless and clients ignore the value, so removing the header offers no functional benefit and most operators leave the default in place.
Values
1.0
The only value observed in practice. Version 1.0
corresponds to the original MIME specification published
in 1996. No subsequent MIME version has been
standardized, so every MIME-Version header contains this
same value.
Example
A typical response from a web server including
MIME-Version alongside the standard
Content-Type header. The 1.0 value
indicates MIME version 1.0, the only version defined.
MIME-Version: 1.0
Content-Type: text/html; charset=UTF-8
PDF generation endpoints and document export services
frequently include the header because the underlying
libraries produce MIME-formatted output. The value
remains 1.0.
MIME-Version: 1.0
Content-Type: application/pdf
Takeaway
The MIME-Version header is a vestige of the email
MIME specification with no functional role
in HTTP. The value is always 1.0, and HTTP clients
do not act on the header. The
Content-Type header serves the
content description role in HTTP responses.