What does "304" mean in the context of websites?

In the context of websites, a "304" status code means "Not Modified". It's a response from a web server indicating that the requested resource has not been modified since the last time the client accessed it.

Here's a more detailed explanation:

How it Works:

1. Initial Request: When a browser (or any client) requests a resource (like an HTML page, image, or CSS file) for the first time, the server sends the resource along with a "200 OK" status code and some headers, including caching headers like `Last-Modified` or `ETag`.

2. Subsequent Requests: On subsequent requests for the same resource, the browser includes the `Last-Modified` or `ETag` value in the request headers (using `If-Modified-Since` or `If-None-Match` headers, respectively).

3. Server Check: The server checks if the resource has been modified since the date/time specified in the `If-Modified-Since` header or if the `ETag` value matches the current version of the resource.

4. 304 Response: If the resource has not been modified, the server responds with a "304 Not Modified" status code. The server does not send the resource's content again. Instead, it sends a minimal response with headers indicating that the cached version is still valid.

5. Browser Action: Upon receiving a 304 response, the browser uses its cached copy of the resource, saving bandwidth and improving page load times.

Key Benefits of 304 Responses:

- Reduced Bandwidth Usage: By not sending the same content repeatedly, 304 responses significantly reduce the amount of data transferred over the network.

- Faster Page Load Times: Since the browser uses its cached copy, pages load faster, providing a better user experience.

- Reduced Server Load: Servers don't have to process and send the same content repeatedly, reducing server load and improving scalability.

Common Use Cases:

- Static Assets: Images, CSS files, JavaScript files, and other static assets are prime candidates for 304 responses.

- API Responses: APIs can also use 304 responses to indicate that data has not changed since the last request.

In Summary:

A 304 status code is a crucial part of HTTP caching, allowing browsers to efficiently reuse cached resources, leading to faster and more efficient web browsing. It indicates that the requested resource has not changed, and the browser can safely use its cached copy.

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