Trailer

The HTTP Trailer request and response header allows the sender to include additional fields at the end of chunked messages in order to supply metadata that might be dynamically generated while the message body is sent.

Note: The TE request header needs to be set to trailers to allow trailer fields.

Warning: Developers cannot access HTTP trailers via the Fetch API or XHR. Additionally, browsers ignore HTTP trailers, with the exception of Server-Timing. See Browser compatibility for more information.

Header type Request header, Response header, Content header
Forbidden header name Yes

Syntax

http
Trailer: header-names

Directives

header-names

HTTP header fields which will be present in the trailer part of chunked messages. The following header names are disallowed:

Examples

Server-Timing as HTTP trailer

Some browsers support showing server timing data in developer tools when the Server-Timing header is sent as a trailer. In the following response, the Trailer header is used to indicate that a Server-Timing header will follow the response body. A metric custom-metric with a duration of 123.4 milliseconds is sent:

http
HTTP/1.1 200 OK
Transfer-Encoding: chunked
Trailer: Server-Timing

--- response body ---
Server-Timing: custom-metric;dur=123.4

Specifications

Specification
HTTP Semantics
# field.trailer
HTTP/1.1
# chunked.trailer.section

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobile
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Trailer

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
Partial support
Partial support
No support
No support

See also