Chrome extension · Developer Tools · v1.0.1
Core Web Vitals (iframes)
Real Core Web Vitals for every iframe on the page — not just the top frame
Core Web Vitals (iframes) is a free Chrome extension that measures LCP, CLS, INP, FCP and TTFB separately for a page and for every iframe on it, using Google's web-vitals library inside each frame. It shows each frame's numbers in a popup and a small in-page badge, rates them good, needs improvement or poor, and can highlight the element behind an LCP, CLS or INP value.
- Plans
- Free
What does Core Web Vitals (iframes) do?
Per-frame Core Web Vitals
See LCP, CLS, INP, FCP and TTFB measured separately for the top page and every iframe on it, instead of one set of numbers for the whole page.
Every frame, including dynamic ones
The measuring script runs in every frame from the moment it starts loading, including iframes added after the page loads and about:blank frames.
Pinpoint the culprit element
An aim button on LCP, CLS and INP highlights the element responsible, inside the frame it actually lives in. Toggle LCP, CLS or INP in the popup to keep the outline on.
Colour-coded thresholds
Every metric is rated good, needs improvement or poor against the web.dev thresholds, and the toolbar icon takes the colour of the worst LCP among the tab's frames.
Exportable JSON
Copy any single metric, or every frame's metrics at once, as JSON, ready to paste into a bug report or a regression spreadsheet.
When should you use Core Web Vitals (iframes)?
When a page's speed depends on what loads in iframes, such as an embedded checkout or payment form, a video or map, an ad slot, or a chat or reviews widget. Most tools report one set of numbers for the top page. This one shows each frame's own LCP, CLS and INP beside the page's, so you can tell whether the embed or the page around it is the slow part, then aim at the element responsible.
What doesn't Core Web Vitals (iframes) measure?
It measures your own visit, in your browser, on your device and network. It doesn't fetch field data from real users, such as the Chrome UX Report, so its numbers can differ from reports built on that data. INP appears only after you interact, CLS and INP keep changing while you use the page, and a sandboxed iframe the extension can't run in reports nothing.
How much does Core Web Vitals (iframes) cost?
Core Web Vitals (iframes) is free to install from the Chrome Web Store.
| Plan | Price | What it includes |
|---|---|---|
| Free | Free |
|
Plans and prices as listed on the Chrome Web Store, which is authoritative. Page updated .
What can Core Web Vitals (iframes) access?
The Chrome permissions in Core Web Vitals (iframes)’s manifest, and what each one is for.
| Permission | What it allows | Why |
|---|---|---|
| <all_urls> | Run a script in every frame of every website | To measure Core Web Vitals inside each frame and draw the in-page badge. |
| activeTab | Access the tab you open the popup on | Declared with site access so the popup works on the tab you're looking at. |
| tabs | See your open tabs | To find the active tab and colour its toolbar badge. |
| webNavigation | Know when a tab moves to a new page | To start fresh measurements when the top page's address changes. |
| storage | Save data in Chrome's extension storage | To keep each tab's numbers until Chrome restarts, and your display settings. |
It sends no data anywhere and asks for no access to cookies or browsing history.
Frequently asked questions
Is Core Web Vitals (iframes) free?
Yes. It's free to install from the Chrome Web Store, with no account or signup, and the extension sends no data anywhere.
Why are its numbers different from other speed reports?
Because it measures only the visit in front of you, in your browser. A report built from many visitors' data, or from a test run on another machine, measures different visits on different devices and networks. Use this extension to find which frame and which element is slow, not as your official score.
What does the coloured toolbar badge mean?
It shows the worst LCP rating among the tab's frames: green for good, amber for needs improvement, red for poor. It covers LCP only; open the popup for CLS, INP, FCP and TTFB in each frame.
Can I hide the badges it adds to pages?
Yes. Click × on a badge to hide it in that frame, or switch Badges off in the popup to remove it from every frame. The extension keeps measuring either way, and the popup still shows every frame's numbers.
When do the numbers reset?
When you reload the page, go to a different address in the tab, or click Clear all metrics for this tab. They are kept only until Chrome restarts.
Install Core Web Vitals (iframes) from the Chrome Web Store.
Need help with Core Web Vitals (iframes)? Email chrome@afixer.app.