How to Check Blog Speed: LCP, INP and CLS Explained

To check blog performance, analyze a public URL in PageSpeed Insights, compare mobile and desktop, and use LCP, INP and CLS to assess loading, responsiveness and layout stability. Separate real-user data from lab diagnostics, then address the cause behind a poor metric rather than focusing on a single performance score.

What are LCP, INP and CLS?

Core Web Vitals are Google's core measures of web user experience. The current set includes the three metrics below. Lower values are better for all three, but they measure different things and use different units.

Google's Web Vitals guidance uses the 75th percentile, assessed separately for mobile and desktop. This looks beyond the fastest single visit toward the experience a substantial share of visitors receive.

A post might appear quickly but respond slowly when someone opens its menu. Another might respond well yet push the article down when an ad arrives. Identify which experience is poor before repeatedly compressing images to solve an undefined “speed” problem.

Run a PageSpeed Insights check

1. Choose an article URL that opens without signing in. Exclude editor and preview addresses.
2. Enter it in PageSpeed Insights and run the analysis.
3. In the mobile result, read real-user experience separately from performance diagnostics.
4. Check desktop too. Record the URL, date, device category, poor metrics and main findings.

Instead of checking only the latest article, choose representative page types. An ordinary text article, an image-heavy post and a page with tables or code can help distinguish shared template issues from content-specific ones. Use the formats your blog actually contains.

Check whether the analyzed URL differs from the one you entered. If a redirect sends the test elsewhere, use that same final destination in later comparisons. Consistent records are useful for judging changes, rather than making the score look better.

Separate field data from the performance score

Real-user data comes from the Chrome User Experience Report, or CrUX, over the previous 28 days. With insufficient samples, the result may show origin-level data or no field data. Lab diagnostics instead use Lighthouse in a simulated environment. The PageSpeed Insights documentation explains the distinction.

A performance score of 90 and a real-user Core Web Vitals pass are different assessments. Check whether field data represents the specific URL or the whole origin. Missing data is neither a certificate of good performance nor proof of a problem.

For example, replacing an image might improve a lab result immediately, while the rolling field-data period still includes visits from before the change. First verify that the replacement loads correctly and that comparable tests show signs of improvement. Review the real-user trend over time separately.

For poor LCP, find what delays the main content

Start by identifying the element reported as the largest content. It may be the article's top image, a large text block or something else. Do not apply the same image setting everywhere without checking the actual element.

• If it is an image, compare its delivered dimensions with its displayed size.
• Use suitable dimensions, compression and format while checking necessary detail and text clarity.
• Check whether the first-screen LCP image is being lazy-loaded. A setting useful for images farther down the article can delay the main image.
• If the diagnostics identify server response or render-blocking resources, investigate those causes too.

The LCP optimization guide separates delays in discovering, transferring and displaying content. If a format change is appropriate, see how to convert images to WebP. If visitors still receive the old file afterward, check caching and the resource actually requested.

For poor INP, inspect work after interaction

INP assesses responsiveness through the next visual update after an interaction. Long JavaScript tasks can occupy the browser's main thread and delay input handling. The INP optimization guide examines input delay, event processing and presentation delay.

As a blog operator, first reproduce practical actions on mobile: opening the menu, using search and following a table-of-contents link. Record which action feels delayed, then review unnecessary or duplicate plugins, widgets and external scripts active on that page.

Avoid disabling many plugins at once. Prepare a backup or test environment and make one change at a time so you can identify its effect. If you enable delayed JavaScript execution, verify that menus, search and consent controls still work, alongside checking the score.

For poor CLS, reserve space for moving content

Late images, ads and embeds can push the article or a link someone is about to tap. The CLS optimization guide highlights image dimensions and reserving space for late-loading content.

• Provide image width and height or a suitable reserved aspect ratio.
• Reserve appropriate space for ads and video embeds at each device size.
• Check that an unfilled ad slot does not suddenly collapse and create another shift.
• Watch for text and buttons moving when fonts or banners appear.

Reducing empty space and keeping the layout stable may require a compromise. Do not assume a desktop ad height is suitable for mobile. Open real articles and inspect movement near the top, middle and bottom of the screen.

Recheck under comparable conditions

1. Save the original settings, files and test results.
2. Choose one important cause and make a targeted change.
3. Refresh relevant caches and verify the changed resource on the public page.
4. Retest the same URL and device category, then check menus, images, ads and article layout.
5. If functionality breaks or other metrics worsen, restore the change and narrow the cause again.

Do not declare success from a small difference in one run. Compare your records and recurring issues before making the next change. A higher score achieved by breaking something readers need is not a useful improvement.