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The cost of a slow website:
Why you lose sales
and security on Google

24 April 2026 · 6 min read Development

Google has been using Core Web Vitals as a ranking factor since 2021. But there is something few mention: technical improvements that raise the Lighthouse score also reduce your website's attack surface. It's no coincidence — performance best practices and security best practices overlap more than they appear.

What are Core Web Vitals?

They are three metrics Google uses to measure real user experience on a webpage. They have been part of the ranking algorithm since May 2021.

LCP
Largest Contentful Paint

Time until the page's main element is visible

Target: < 2.5s
FID / INP
Interaction to Next Paint

Response time to the user's first interaction

Target: < 200ms
CLS
Cumulative Layout Shift

Visual stability: does content move while loading?

Target: < 0.1

The connection between performance and security

This is the article's central point. Many optimizations that improve Core Web Vitals also strengthen security. They are not two separate projects — they are the same work.

Reduce third-party scripts
🚀 Performance

Less JavaScript = faster page. Every external script blocks rendering.

🔒 Security

Every external script is a potential attack surface (supply chain attacks). Fewer dependencies = less risk.

Implement Content Security Policy (CSP)
🚀 Performance

Allows securely preloading critical resources using directives like preload.

🔒 Security

Blocks the execution of unauthorized scripts. It is the main defense against XSS.

Serve resources from your own domain
🚀 Performance

Avoids additional DNS connections to external domains that add latency.

🔒 Security

External resources can change without your knowledge. Serving them yourself keeps them under your control.

Use HTTPS with HSTS
🚀 Performance

HSTS eliminates the HTTP→HTTPS redirect on recurring visits, improving TTFB.

🔒 Security

HSTS forces HTTPS always, even if the user types the URL without a protocol. Prevents downgrade attacks.

Compress and optimize images
🚀 Performance

Images are the biggest factor in LCP. WebP format and lazy loading drastically improve the score.

🔒 Security

Images with EXIF metadata can leak info about the server or uploader. Processing cleans them.

Configure proper caching and HTTP headers
🚀 Performance

Correct Cache-Control makes static resources load from the browser, not the server.

🔒 Security

Security headers (X-Content-Type-Options, X-Frame-Options) go in the exact same server configuration.

How to measure your Core Web Vitals right now

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In our web development projects, performance and security are integrated from day one — not tacked on at the end.

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They are not two separate projects. At Kodia, performance and security are part of the same development process.

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