Does an HTTP 304 response contain a body?

No. A 304 response consists only of headers and terminates with no message body, saving bandwidth and network latency.

How does 304 improve web performance?

By avoiding repeated downloads of large static files (images, CSS, JS), 304 responses reduce bandwidth consumption and accelerate page load times.

How can I test a 304 response with curl?

Run 'curl -I -H "If-Modified-Since: " ' to check if your server returns 304 Not Modified.

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HTTP Status Code Reference

HTTP 304: Not Modified

Conditional request response indicating that the cached version on the client is still fresh and valid.

Status Code

304

Classification

3xx Redirection

Reason Phrase

Not Modified

Specification

RFC 9110, Section 15.4.5

Inspect Live HTTP Headers & Status Codes

Test any URL to verify whether it returns HTTP 304 Not Modified, measure TTFB latency, and trace redirect chains.

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Common Causes & Triggers

The client sent an ETag that matches the server's current ETag.
The resource has not been updated since the date in the If-Modified-Since header.
Browser cache revalidation triggered on page refresh.

Troubleshooting & Resolution

Verify ETag and Last-Modified headers are generated consistently across load-balanced server clusters.
Ensure Cache-Control headers include 'must-revalidate' or 'no-cache' when conditional validation is desired.

Search Engine (Googlebot) SEO Impact

Highly beneficial. Enables search engine crawlers to verify freshness rapidly without wasting crawl budget on unchanged pages.

Inspect via Terminal (cURL)

Execute this command to inspect headers and response codes from your terminal:

curl -I -H 'If-None-Match: "xyz123"' https://example.com/asset.js

Frequently Asked Questions

Technical answers and debugging guidelines for HTTP 304 Not Modified.

It indicates that the requested resource has not changed since your last visit. The server sends no body, instructing your browser to use its cached version.