Partial Content

# Quick Definition

The 206 Partial Content status code indicates that the server is successfully fulfilling a range request by transferring only the portion of the resource specified by the client's Range header. Instead of sending the entire file, the server delivers just the requested byte range along with Content-Range headers describing the returned segment.

# When Does a 206 Response Occur?

A 206 response occurs when the client includes a Range header in the request, asking for specific bytes of a resource, and the server supports and honors that request. This is fundamental to how video players seek through media files, how download managers resume interrupted downloads, and how large files are transferred in chunks.

The server must include a Content-Range header in the response indicating which bytes are being returned and the total size of the resource. For multiple ranges, the response uses a multipart/byteranges content type.

# Common Use Cases

• HTML5 video and audio streaming -- seeking to a specific timestamp without downloading the entire file
• Resumable file downloads -- continuing a large download after a network interruption
• Download managers that split large files into parallel chunk downloads for faster transfers
• PDF viewers that load pages on demand rather than downloading the entire document
• CDN delivery of large static assets using chunked transfers for efficiency

# Best Practices

1. Advertise range support -- Include Accept-Ranges: bytes in your responses to indicate that the server supports range requests for the resource.
2. Include Content-Range and Content-Length -- Always return the correct Content-Range header (e.g., bytes 0-999/5000) and set Content-Length to the size of the returned chunk, not the full file.
3. Use ETag or Last-Modified for validation -- Include validators so clients can detect if the resource changed between range requests, preventing corrupted downloads.
4. Handle invalid ranges gracefully -- Return 416 Range Not Satisfiable if the requested range is outside the resource size, with a Content-Range header indicating the actual size.
5. Support single and multipart ranges -- Implement both single range (one segment) and multipart range (multiple segments in one response) for maximum compatibility.

# HTTP Example

GET /videos/demo.mp4 HTTP/1.1
Host: cdn.example.com
Range: bytes=1048576-2097151

HTTP/1.1 206 Partial Content
Content-Type: video/mp4
Content-Length: 1048576
Content-Range: bytes 1048576-2097151/10485760
Accept-Ranges: bytes
ETag: "a1b2c3d4e5"

[binary data - 1 MB chunk]

# Related Status Codes

# Frequently Asked Questions