Content-Range
The HTTP Content-Range response header indicates which portion of the full resource body is included in the current message.
Usage
The Content-Range header appears in 206 Partial Content responses when a server fulfills a Range request by delivering only part of a resource. The header specifies the byte range of the partial content and the total size of the complete resource.
Range requests enable efficient downloads. A client interrupted during a large file transfer resumes from where the connection dropped instead of starting over. Media players use range requests to seek to specific positions in audio or video files without downloading the entire stream.
Servers advertise range request support through the
Accept-Ranges header, typically set to
bytes. When a range request asks for a byte range beyond the
resource boundary, the server responds with
416 Range Not Satisfiable and includes a
Content-Range header showing the actual resource size.
The syntax follows a structured format with three components:
the unit (almost always bytes), the byte range, and the
complete size.
Content-Range: <unit> <range-start>-<range-end>/<size>
Directives
unit
The unit type for the range. The value bytes is the only
widely implemented unit.
range-start
A zero-based integer indicating the first byte of the returned range.
range-end
A zero-based integer indicating the last byte of the returned range, inclusive.
size
The total size of the complete resource in bytes. An
asterisk (*) replaces the size when the total length is
unknown, as with streaming or dynamically generated content.
Example
A client resumes a download starting at byte 1000 of a file with a total size of 65,000 bytes. The server returns bytes 1000 through 2000 inclusive.
Content-Range: bytes 1000-2000/65000
A streaming resource delivers a range without knowing the total size. The asterisk indicates an unknown complete length.
Content-Range: bytes 1000-2000/*
A server rejects a range request because the requested bytes exceed the resource size. The response carries a 416 Range Not Satisfiable status and reports the actual size.
HTTP/1.1 416 Range Not Satisfiable
Content-Range: bytes */50000
A multipart range response delivers multiple ranges in a
single response. Each part includes its own
Content-Range header within the multipart/byteranges
body.
HTTP/1.1 206 Partial Content
Content-Type: multipart/byteranges; boundary=BOUNDARY
--BOUNDARY
Content-Type: text/plain
Content-Range: bytes 0-499/10000
[first 500 bytes]
--BOUNDARY
Content-Type: text/plain
Content-Range: bytes 9500-9999/10000
[last 500 bytes]
--BOUNDARY--
Takeaway
The Content-Range header identifies the byte range and total size of partial content delivered in a response, enabling resumable downloads, media seeking, and efficient bandwidth use through range requests.