304 Not Modified

What Is a 304 Not Modified Status Code?

A 304 Not Modified is an HTTP status code returned by a server when a client makes a conditional request and the resource has not changed since it was last fetched. Instead of sending the full resource again, the server tells the client to use its cached copy, which dramatically reduces bandwidth consumption and speeds up page delivery.

Conditional requests work through two primary mechanisms: ETag headers and Last-Modified headers. When a browser or crawler first requests a resource, the server includes an ETag (a unique hash of the content) or a Last-Modified timestamp in the response. On subsequent requests, the client sends these values back using If-None-Match or If-Modified-Since headers, allowing the server to determine whether the content has changed.

If the content is unchanged, the server returns a lightweight 304 response with no body, saving the cost of transferring the full resource. This mechanism is fundamental to how HTTP caching works and plays a significant role in both user experience and search engine crawling efficiency.

Why 304 Not Modified Matters for SEO

For search engine optimization, 304 responses directly impact crawl budget efficiency. When Googlebot crawls your site and receives 304 responses for unchanged pages, it consumes far less bandwidth and can crawl more of your site in less time. This is especially valuable for large websites with thousands or millions of pages where crawl budget is a real constraint.

Proper cache validation through 304 responses also improves page speed for returning visitors. Since the browser can serve cached resources instead of downloading them again, pages load significantly faster on repeat visits. This contributes to better server response times and improved user experience metrics that search engines factor into rankings.

Without proper conditional request support, every crawl hit results in a full 200 response with the complete resource body. This wastes server resources, slows down crawling, and can lead to unnecessary strain on your infrastructure during heavy crawl periods.

How to Set Up 304 Not Modified Responses

To enable 304 responses, configure your server to include ETag and Last-Modified headers in responses. In Apache, ETags are typically enabled by default, but you can fine-tune them with the FileETag directive. In Nginx, use the etag on; directive and ensure if_modified_since is set to exact for precise cache validation.

Set appropriate Cache-Control headers alongside your ETags. For static assets like CSS, JavaScript, and images, use long cache durations with Cache-Control: max-age=31536000 combined with file versioning. For HTML pages, use shorter durations like Cache-Control: max-age=3600, must-revalidate to balance freshness with caching benefits.

Verify your 304 implementation by checking server logs for conditional request patterns. Look for requests containing If-None-Match or If-Modified-Since headers and confirm that your server responds with 304 when content is unchanged. You can also use a CDN to handle cache validation at the edge, reducing the load on your origin server while ensuring crawlers and users always receive efficient responses.