What is a 304 Status Code? How to Implement 304 Status Codes

The 304 Not Modified HTTP status code can quietly help your site run faster, serve fewer bytes, and support SEO goals through better caching. At Lotus Titan, we build caching strategies—ETag, conditional headers, proper server setup—into web design and SEO to make sites leaner and smarter. This post walks through what 304 means, how it works, and how to implement it reliably.

---

Table of Contents

---

What Is 304?

The 304 Not Modified status tells a browser that a resource has not changed since it was last fetched. Instead of re-downloading the file, the browser can reuse its cached version. The server still returns relevant headers (e.g. ETag, Cache-Control) but omits the response body. :contentReference[oaicite:0]{index=0}

“A 304 response tells the client: your cached version remains valid — no download needed.”

---

Why 304 Matters for SEO & Performance

Although 304 doesn’t directly raise your search rankings, it supports SEO through better performance, reduced bandwidth use, and more efficient crawling.

• Faster Page Loads: Because fewer bytes are transferred, pages load faster, helping with Core Web Vitals and user experience.
• Reduced Bandwidth & Server Load: Serving cached files instead of retransmitting reduces resource demands on your server and hosting limits. :contentReference[oaicite:1]{index=1}
• Better Crawl Efficiency: Bots can skip unchanged assets and focus crawl budget on fresh content.
• Improved Engagement: Users experience smoother, snappier pages, reducing bounce rates.

---

How 304 Works

304 relies on **conditional requests**—clients ask the server whether a resource has changed. Here’s the typical flow:

• Client sends one of: If-Modified-Since (timestamp) or If-None-Match (ETag) headers.
• Server compares those against its current version.
• If unchanged, server responds with 304 Not Modified (no body). Otherwise, it returns 200 OK with the updated resource. :contentReference[oaicite:2]{index=2}

When both headers are present, the ETag comparison (If-None-Match) typically takes precedence because it’s more precise. :contentReference[oaicite:3]{index=3}

The server must include headers that would appear in a 200 OK response (e.g. ETag, Cache-Control, Expires, Vary) even in the 304 reply. :contentReference[oaicite:4]{index=4}

---

Implementing 304 Effectively

Here’s how Lotus Titan configures 304 logic in sites we build, combining caching, headers, and server setup.

1. Cache-Control & Expiry Headers

Define how long resources remain fresh. Common directives:

• public — allows caching in browsers and shared proxies/CDNs
• private — caches only in the user’s browser
• max-age=SECONDS — how long the resource is fresh
• must-revalidate — forces validation after expiry

When both Expires and Cache-Control exist, Cache-Control is honored over Expires. :contentReference[oaicite:5]{index=5}

2. ETag & Last-Modified Headers

Use both headers for fallback and precision. ETag offers fine-grained validation; Last-Modified is a timestamp fallback.

Header	Purpose	Nuances / Best Practices
Last-Modified / If-Modified-Since	Timestamp when resource last changed.	Coarser precision; file-touching or build timestamps can cause false mismatches.
ETag / If-None-Match	Unique identifier (e.g. hash) of resource current version.	Preferred for accuracy; must be consistent across server instances (if load-balanced). :contentReference[oaicite:6]{index=6}
Cache-Control: max-age / public / private	Controls caching scope and duration.	Overrides Expires; use must-revalidate when stricter freshness is needed.

3. Server & CDN Configuration

• Apache: enable modules such as mod_cache, mod_headers, mod_expires
• NGINX: configure etag, add_header, and location blocks for validation logic
• CDNs / Edge Proxies: preserve headers and avoid stripping ETag or Cache-Control during caching passes

4. Monitoring & Validation

Test and log your caching behavior using:

• Chrome DevTools (Network tab → filter “304”)
• GTmetrix, Lighthouse, PageSpeed Insights
• Server logs of header responses / cache hit vs miss metrics

---

---

Troubleshooting & Pitfalls

Stale 304s / No Updates

If ETag or Last-Modified isn’t updated when content changes, the browser may incorrectly keep showing old content. Always regenerate those headers on deploy or content updates.

Inconsistent ETag Across Servers

On load-balanced setups, each server must produce identical ETag logic. If one returns a different ETag, clients may ignore cache correctly. :contentReference[oaicite:7]{index=7}

CDN or Proxy Stripping Headers

Some caching proxies or CDNs may remove validation headers or override cache settings. Test behavior across edge and origin layers.

Browser Cache & DevTools Behavior

Browser dev tools or forced reloads may disable caching logic temporarily, causing false impressions. Test in incognito or with cache disabled toggles off for accurate results.

---

Conclusion & Next Steps

The 304 Not Modified status code is a powerful, efficient tool for caching and performance optimization. While it doesn’t directly raise rankings, it supports SEO through improved speed, lower server load, and better crawl efficiency. At Lotus Titan, caching strategy is baked into our web design and SEO optimization services.

“When caching is configured precisely, a 304 response keeps your website fast, fresh, and efficient.”

👉 Ready to optimize your site’s performance and support SEO gains? Request a Proposal from Lotus Titan to get caching and SEO aligned for your success.