Is this the same as PageSpeed Insights?

No. PageSpeed Insights runs Lighthouse throttling and field data when available. This tool uses a lighter heuristic from one fetch in your session.

Can I upload a HAR file?

Not in this tool. Paste a URL instead. A HAR would need a separate parser path.

Why is my CLS always low?

The model only infers risk from image attributes in the HTML snippet. Real CLS depends on fonts, ads, and runtime layout shifts this parser cannot see.

Should I file tickets from this alone?

Use it to decide what to measure next. Confirm regressions with RUM, synthetic monitoring, or Lighthouse traces before prioritizing sprints.

Technical SEO

Live

Core Web Vitals Estimator

Estimate LCP, INP, and CLS heuristics from a live URL fetch and HTML parse.

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URL

Estimates LCP, CLS, INP from HTML weight + asset profile + compression. Not a substitute for real-world Lighthouse.

Start here · What does this estimator do?

Core Web Vitals measure real user experience: how fast the biggest content paints, how stable the layout is, and how responsive the page feels.

This tool does not read Chrome field data. It fetches the URL once, parses the HTML, counts scripts and stylesheets, inspects image hints, and reads response headers such as compression.

The LCP estimate blends round-trip time with heuristics for decoding and render-blocking resources. CLS and INP outputs are coarse bands derived from counts and image patterns.

When to use this tool

Quick before-and-after on a template
Deploy a performance tweak, paste the same URL, and compare estimated LCP plus blocking script counts.
Triage blocking JavaScript
Use blocking script totals as a clue when INP shows needs improvement. Async and defer reduce blocking counts in the model.
Check compression headers
See whether gzip or Brotli is present. Missing compression often inflates the crude decode portion of the estimate.
Image layout risk scan
Large images without lazy loading can bump the CLS band upward. Pair results with your design system rules.

Examples

Walk through these with the form above — they are practice scenarios, not live data.

Marketing landing page

Try this

Paste the public URL for a campaign page that loads several third-party scripts.

What to look for

If blocking scripts are high, test removing or deferring vendors, then rerun. Watch estimated LCP move with decode and blocking estimates.

Documentation site

Try this

Paste a docs URL that mostly ships static HTML with many code blocks and images.

What to look for

Compare lazy-loaded images versus large static widths. Good compression should show as gzip or br true.

Short tutorial

Follow in order the first time you use the tool; later you can skip to the step you need.

Step 1 — Paste a public https URL
Start with one representative page. Logged-in or geo-blocked URLs may error in the fetch API.
Step 2 — Run estimate
Wait for fetch plus header probes to finish. Errors surface when the URL cannot be retrieved.
Step 3 — Read LCP, CLS, and INP bands
LCP shows milliseconds with good, needs improvement, or poor labels. CLS shows low, medium, or high. INP shows good, needs improvement, or poor.
Step 4 — Inspect counts
Scripts, blocking scripts, styles, and image counts explain why the model scored the way it did.
Step 5 — Confirm in Real User Monitoring
Ship a fix, then verify in Search Console Core Web Vitals or your RUM tool. This page is a fast lab-style hint only.

More detail

New here? Skim Start here first, then run one Examples scenario in the form above.

Core Web Vitals Estimator does one job: estimate LCP, INP, and CLS heuristics from a live URL fetch and HTML parse. It lives under Technical SEO on SEOToolkits, where the beginner idea is simple: Technical SEO keeps pages crawlable, indexable, fast enough, and understandable to search engines.

FAQ

Is this the same as PageSpeed Insights?: No. PageSpeed Insights runs Lighthouse throttling and field data when available. This tool uses a lighter heuristic from one fetch in your session.
Can I upload a HAR file?: Not in this tool. Paste a URL instead. A HAR would need a separate parser path.
Why is my CLS always low?: The model only infers risk from image attributes in the HTML snippet. Real CLS depends on fonts, ads, and runtime layout shifts this parser cannot see.
Should I file tickets from this alone?: Use it to decide what to measure next. Confirm regressions with RUM, synthetic monitoring, or Lighthouse traces before prioritizing sprints.