Vary Header
The Vary header is an HTTP response header that tells caches, CDNs, and browsers which request headers should be considered when determining whether a cached response can be reused.
Explained
The Vary header is an HTTP response header that tells caches, CDNs, and browsers which request headers should be considered when determining whether a cached response can be reused. It signals that your server provides different content variations based on specific characteristics of the incoming request, such as device type, language preference, or geographic location.
How It Works
The Vary header creates cache keys that include the specified header values. For example:
- Standard cache key: https://example.com/page
- With Vary: User-Agent: https://example.com/page + "Mozilla/5.0 (iPhone…)"
- Multiple variations: https://example.com/page + User-Agent + Accept-Language
This mechanism enables sophisticated content delivery strategies while maintaining optimal caching efficiency, allowing marketing teams to serve highly targeted content variations without sacrificing site speed or SEO performance.
Common Values
- User-Agent: For device-optimized experiences and mobile conversions
- Accept-Language: For international market penetration
- Accept-Encoding: For compression optimization (typically automatic)
- Authorization: For personalized logged-in experiences