Understanding Category Scores and Web Performance Metrics

This guide explains the key scoring categories and performance metrics used to evaluate website quality, accessibility, and user experience. It also provides optimization tips to help improve your site’s performance.

Category Scores #

Performance #

Measures how fast your page loads and becomes interactive, based on Core Web Vitals and other performance metrics.

• Good: 90–100 (Green)
• Average: 50–89 (Orange)
• Poor: 0–49 (Red)

Accessibility #

Evaluates how accessible your site is to users with disabilities. Checks include ARIA labels, color contrast, and keyboard navigation.

• Good: 90–100 (Green)
• Average: 50–89 (Orange)
• Poor: 0–49 (Red)

Best Practices #

Assesses modern web development standards such as HTTPS usage, console errors, deprecated APIs, and security issues.

• Good: 90–100 (Green)
• Average: 50–89 (Orange)
• Poor: 0–49 (Red)

SEO #

Measures how well your page is optimized for search engines, including meta tags, mobile-friendliness, and structured data.

• Good: 90–100 (Green)
• Average: 50–89 (Orange)
• Poor: 0–49 (Red)

Core Web Vitals #

Core Web Vitals are Google’s key metrics for measuring real-world user experience. They are part of the page experience signals used in search ranking.

Largest Contentful Paint (LCP) #

Measures loading performance by tracking when the largest content element becomes visible.

• Good: < 2.5s
• Needs Improvement: 2.5–4.0s
• Poor: > 4.0s

Optimization Tips:

• Compress and optimize images
• Preload critical resources
• Reduce CSS/JavaScript blocking time
• Use a CDN for faster delivery

First Input Delay (FID) / Total Blocking Time (TBT) #

Measures interactivity. FID tracks delay in user input response, while TBT measures JavaScript blocking time.

• Good: < 100ms (FID) / < 200ms (TBT)
• Needs Improvement: 100–300ms (FID) / 200–600ms (TBT)
• Poor: > 300ms (FID) / > 600ms (TBT)

Optimization Tips:

• Break up long JavaScript tasks
• Remove unused scripts
• Use code splitting and lazy loading
• Limit third-party script impact

Cumulative Layout Shift (CLS) #

Measures visual stability by quantifying unexpected layout shifts.

• Good: < 0.1
• Needs Improvement: 0.1–0.25
• Poor: > 0.25

Optimization Tips:

• Define size attributes for images/videos
• Reserve space for ads
• Avoid inserting content above existing elements
• Use CSS transforms instead of layout-triggering properties

Other Important Metrics #

First Contentful Paint (FCP) #

Measures when the first text or image appears.

• Good: < 1.8s
• Needs Improvement: 1.8–3.0s
• Poor: > 3.0s

Optimization Tips:

• Eliminate render-blocking resources
• Minify CSS/JavaScript
• Remove unused CSS
• Apply efficient caching

Speed Index #

Shows how quickly content is visually displayed during page load.

• Good: < 3.4s
• Needs Improvement: 3.4–5.8s
• Poor: > 5.8s

Optimization Tips:

• Reduce main thread work
• Optimize JavaScript execution
• Ensure text visibility during font load
• Minimize request depth

Time to Interactive (TTI) #

Measures when the page becomes fully interactive.

• Good: < 3.8s
• Needs Improvement: 3.8–7.3s
• Poor: > 7.3s

Optimization Tips:

• Reduce JavaScript execution time
• Limit third-party code
• Minimize main thread work
• Keep requests and transfer sizes small

Diagnostics #

Server Response Time (TTFB) #

Time until the server sends the first byte.

• Good: < 600ms
• Poor: > 1000ms

DOM Size #

Total number of DOM elements.

• Good: < 1,500 elements
• Poor: > 3,000 elements

JavaScript Execution Time #

Time spent parsing, compiling, and executing JavaScript.

• Good: < 2s
• Poor: > 3.5s

Render Blocking Resources #

Resources that delay initial rendering.

• Good: 0 resources
• Poor: 3+ resources