Performance
PageSpeed Insights and Core Web Vitals, when a PageSpeed key is set.
Real-user Cumulative Layout Shift is high
Section titled “Real-user Cumulative Layout Shift is high”performance.crux.cls_slow · Issue · Severity: High
Why it matters. Layout movement makes reading and interaction unstable, especially when users try to click or focus content while the page is loading.
How to fix. Reserve space for media and dynamic content, and review late-loading fonts, banners and layout changes.
Real-user Interaction to Next Paint is slow
Section titled “Real-user Interaction to Next Paint is slow”performance.crux.inp_slow · Issue · Severity: High
Why it matters. Slow interaction response makes controls feel unresponsive and can prevent users from completing tasks confidently.
How to fix. Reduce long main-thread tasks, expensive event handlers and third-party script work on the affected interaction.
Real-user Largest Contentful Paint is slow
Section titled “Real-user Largest Contentful Paint is slow”performance.crux.lcp_slow · Issue · Severity: High
Why it matters. Visitors wait longer for the page’s main content to appear, which can reduce confidence and increase abandonment.
How to fix. Identify the main visible element and reduce server, rendering, image or font delays affecting its appearance.
Cumulative Layout Shift is high
Section titled “Cumulative Layout Shift is high”performance.psi.cls_slow · Issue · Severity: High
Why it matters. Layout movement can hide content or cause users to activate the wrong control while the page loads.
How to fix. Reserve dimensions for images and dynamic regions and prevent content from shifting during load.
No real-user performance data is available
Section titled “No real-user performance data is available”performance.psi.crux_unavailable · Coverage (what could not be measured) · Severity: Info
Why it matters. The attempted measurement could not provide usable evidence. No website defect or score penalty is asserted.
How to fix. Review the captured evidence and the documented measurement limitations; verify any change using the same source.
The performance measurement could not be completed
Section titled “The performance measurement could not be completed”performance.psi.failed · Coverage (what could not be measured) · Severity: Info
Why it matters. The attempted measurement could not provide usable evidence. No website defect or score penalty is asserted.
How to fix. Review the captured evidence and the documented measurement limitations; verify any change using the same source.
Web fonts may delay visible text
Section titled “Web fonts may delay visible text”performance.psi.font_display · Issue · Severity: Low
Why it matters. Fonts without an appropriate display strategy can leave text invisible or cause a disruptive font swap during loading.
How to fix. Configure an appropriate font-display strategy and verify that text remains visible during font loading.
The page has an image delivery optimization opportunity
Section titled “The page has an image delivery optimization opportunity”performance.psi.image_formats · Issue · Severity: Medium
Why it matters. Inefficient image formats can transfer substantially more data than necessary and slow visual loading, especially on mobile connections.
How to fix. Use an efficient image format and confirm the delivered dimensions match the rendered size.
Largest Contentful Paint is slow
Section titled “Largest Contentful Paint is slow”performance.psi.lcp_slow · Issue · Severity: High
Why it matters. A slow Largest Contentful Paint means the page’s main visible content is not presented quickly under the tested conditions.
How to fix. Review the main content path, server response, images, fonts and render-blocking resources affecting LCP.
Render-blocking resources delay the first render
Section titled “Render-blocking resources delay the first render”performance.psi.render_blocking · Issue · Severity: Medium
Why it matters. Render-blocking resources delay the browser from displaying useful content and increase the time visitors see an incomplete page.
How to fix. Defer or reduce non-critical CSS and JavaScript that blocks first render.
The Lighthouse performance score is low
Section titled “The Lighthouse performance score is low”performance.psi.score_low · Issue · Severity: High
Why it matters. A low lab score signals potential loading, interaction or visual-stability problems under the tested conditions.
How to fix. Review render-blocking resources, image weight, third-party scripts and custom code on the affected page.
Total Blocking Time is high
Section titled “Total Blocking Time is high”performance.psi.tbt_slow · Issue · Severity: Medium
Why it matters. Long main-thread tasks delay input handling and make the page feel unresponsive during loading.
How to fix. Split or defer long JavaScript tasks and review third-party scripts that block the main thread.
Time to First Byte is slow
Section titled “Time to First Byte is slow”performance.psi.ttfb_slow · Issue · Severity: Medium
Why it matters. A slow server response delays every later loading step and makes the page begin rendering late.
How to fix. Review hosting, redirects, server response time and caching before optimizing later loading steps.
The page may ship unneeded CSS
Section titled “The page may ship unneeded CSS”performance.psi.unused_css · Issue · Severity: Low
Why it matters. Unused CSS increases transferred and parsed code and adds avoidable work before the browser finishes styling the page.
How to fix. Remove unused styles or reduce the CSS loaded on the affected page.
The page may ship unneeded JavaScript
Section titled “The page may ship unneeded JavaScript”performance.psi.unused_js · Issue · Severity: Medium
Why it matters. Unneeded JavaScript consumes bandwidth and processing time and can delay interaction without helping the initial experience.
How to fix. Remove, defer or scope JavaScript that is not needed for the initial page experience.