304 Not Modified

What Is 304 Not Modified?

304 Not Modified is a message that a web server sends to a browser or a bot to say, “This page is the same as last time. Use your saved version.”

It is an HTTP status code in the 3xx group, which is used for redirection and telling clients how to handle a request.

Definition

304 Not Modified is an HTTP response code that means:

• The browser or bot asked for a page, image, or file with a condition, such as “only if it changed”.
• The server checked the file and saw it has not changed since the last visit.
• The server replies with 304 Not Modified and does not resend the full file.

The browser then uses the version stored in its cache instead of downloading it again.

Why 304 Not Modified Matters

304 Not Modified is important for several reasons.

• Faster loading Pages can load faster because the browser does not need to download big files again.
• Less data used It saves bandwidth for both the user and the website owner.
• Better user experience Visitors see pages more quickly, which makes the site feel smoother.
• SEO and crawling Search engine bots can spend less time re-downloading the same content and more time finding new or updated pages. This helps use crawl budget more wisely.

How 304 Not Modified Works

Here is a simple view of how it works between a browser and a server.

1. The first time you visit a page, the server sends a normal response such as 200 OK plus the full content.
2. The response also includes caching headers such as Last-Modified or ETag. The browser saves these values.
3. Next time you visit, the browser sends a conditional request with headers like If-Modified-Since or If-None-Match asking if the file has changed.
4. If the file is the same, the server responds with 304 Not Modified and no body.
5. The browser shows the cached copy it already has.

304 Not Modified vs Related Status Codes

• 304 Not Modified vs 200 OK
  200 OK sends the full content again. 304 Not Modified sends no content and tells the browser to use its cached version. 304 is usually faster.
• 304 Not Modified vs 301 Moved Permanently
  301 says the page has moved to a new URL and gives the new address. 304 says the page is still at the same URL and has not changed.
• 304 Not Modified vs 404 Not Found
  404 means the page does not exist. 304 means the page does exist and is unchanged.

Example of 304 Not Modified

Imagine you visit https://example.com/logo.png every day.

• Day 1, the server sends 200 OK and the full image. Your browser saves it in cache.
• Day 2, your browser asks, “Has logo.png changed since yesterday?”
• The server checks the file, sees it is the same, and sends 304 Not Modified.
• Your browser shows the saved image without downloading it again.

FAQs

Is 304 Not Modified an error?
No, 304 Not Modified is not an error. It is a normal and helpful response that improves speed and saves data.

Does 304 Not Modified affect SEO?
Yes, in a good way. It helps search engines crawl your site more efficiently by not wasting time and bandwidth on unchanged content.

How can I enable 304 Not Modified on my site?
You enable it by setting proper cache headers like Last-Modified, ETag, Cache-Control, and Expires on your server. Most web servers and CDNs can do this through their settings or config files.

Why do I sometimes see 304 Not Modified in logs but not in the browser?
Developer tools and server logs often show the 304 response, but the browser quietly uses the cached version, so the page still appears normal and fast to users.