Content · Request & Response

Content-Length

The size of the body in bytes.

What is Content-Length?

Content-Length declares the exact size of the message body in bytes. Clients use it to allocate a buffer, show progress bars, and know when the body ends when connection reuse (keep-alive) is in play.

Typical usage

Set automatically by web servers. Only manually set when writing raw HTTP.

Examples

Content-Length: 348

Common gotchas

Content-Length is mutually exclusive with Transfer-Encoding: chunked. Sending both is an HTTP protocol error.

Specification

RFC 9110 §8.6

Related headers

Content-Type

Declares the media type of the body.

Content-Encoding

How the body has been transparently encoded (usually compressed).

Content-Disposition

Controls whether a resource is displayed inline or triggered as a download.