HTTP 304 Not Modified: What It Means and How to Fix Problems

What 304 means

The status code 304 Not Modified tells the browser: "The file has not changed since you last got it, so use your saved copy." It saves bandwidth and makes sites faster.

Normally you do not need to fix a 304. Act only if visitors keep seeing old content after an update.

Common causes

• Cached content that does not refresh. The browser or a cache keeps the old file.
• Wrong server headers. Cache headers say that the file is still fresh.
• **Wrong ETag or Last-Modified values.** The server says "not modified" when the file did change.
• A proxy or CDN that serves an old copy.
• Browser cache settings.

Diagnose it

• Browser developer tools. Press F12, open the Network tab and reload. Look at the status, the ETag, Last-Modified and Cache-Control headers.
• Server logs. Look for 304 responses for the files you changed.
• cURL. Check the headers from the command line:

curl -I https://example.com/style.css

Send a conditional request to test:

curl -I -H "If-None-Match: \"etag-value\"" https://example.com/style.css

Fix it as a visitor

1. Clear the browser cache.

   

2. Open the page in a private (incognito) window.

   

3. Turn off the cache while developer tools are open. In the Network tab, tick Disable cache.

   

4. Try another browser or device.

   

5. Do a hard reload with Ctrl + F5 (Cmd + Shift + R on a Mac).

Fix it as a site owner

• Correct the headers. Check Cache-Control, ETag and Last-Modified.
• Remove long caching for files that change often.
• Use correct date formats for Last-Modified (HTTP date format).
• Turn off server caching if it serves old pages, or purge it after an update.
• Update the CDN or proxy rules, and purge their cache.

Best practices

• Use proper cache headers.
• Set a reasonable expiry time.
• Version your assets (style.css?v=2 or file names with a hash), so a change forces a new download.
• Watch your logs.

Quick recap

• 304 is normal and saves bandwidth.
• If old content shows, clear caches and purge the CDN.
• Version your files so updates always reach visitors.