Why am I always getting 200 instead of 304?

Your server may not be comparing conditional headers. Verify it reads If-Modified-Since/If-None-Match and returns 304 when appropriate. Also check that Last-Modified/ETag headers are sent on initial responses.

Do CDNs handle conditional requests automatically?

Most CDNs handle conditional requests between client and CDN automatically. Origin-to-CDN conditional requests may need explicit configuration, especially for dynamic content.

If-Modified-Since Caching — Conditional Request and 304 Not Modified Errors

Informational3xx redirection

Overview

Fix If-Modified-Since and If-None-Match conditional caching errors causing stale content, cache validation failures, and unnecessary full downloads.

Key Details

Conditional requests use If-Modified-Since or If-None-Match headers to validate cached content
Server responds with 304 Not Modified if the content has not changed, saving bandwidth
If-Modified-Since uses a date; If-None-Match uses an ETag (entity tag) for more precise validation
Incorrect date formats or clock skew between client and server cause validation failures
Some servers do not support conditional requests, always returning full 200 responses

Common Causes

Server not sending Last-Modified or ETag headers on initial responses
Date format in If-Modified-Since not matching the required HTTP date format (RFC 7231)
Clock skew between client and server causing premature or delayed cache invalidation
Load-balanced servers generating different ETags for the same content

Steps

1Ensure your server sends Last-Modified and ETag headers on cacheable responses
2Implement conditional request handling: compare If-Modified-Since/If-None-Match and return 304 when content is unchanged
3Use strong ETags based on content hash (not timestamp) for consistent validation across load-balanced servers
4Test conditional requests: curl -H 'If-None-Match: "etag-value"' -v https://your-server.com/resource
5Configure your CDN to support and forward conditional request headers to the origin

More in 3xx Redirection

http-300-multiple-choicesHTTP 300 Multiple Choices — What It Means & How to Fix It

Warning

http-301-moved-permanentlyHTTP 301 Moved Permanently — What It Means & How to Fix It

Warning

http-302-foundHTTP 302 Found — What It Means & How to Fix It

Warning

http-303-see-otherHTTP 303 See Other — What It Means & How to Fix It

Warning

http-304-not-modifiedHTTP 304 Not Modified — What It Means & How to Fix It

Warning

http-305-use-proxyHTTP 305 Use Proxy — What It Means & How to Fix It

Warning

Frequently Asked Questions

If-Modified-Since uses a date and is simpler but less precise. If-None-Match uses ETags (content fingerprints) and is more reliable, especially with load-balanced servers generating the same content.