Everything you need to make pages lighter
Built for developers, designers, agencies and sustainability teams.
Eco Score, A–F
One 0–100 score blending carbon, page weight, green hosting and best practices — inspired by Lighthouse.
Carbon estimate
Grams of CO₂ per view and a yearly projection, using CO2.js (Sustainable Web Design model).
Green hosting check
Instantly see whether the site runs on green energy via The Green Web Foundation.
Page-weight breakdown
Transferred bytes by type — HTML, JS, CSS, images, fonts, video — plus third-party share.
Actionable fixes
Prioritized recommendations: oversized images, heavy JS, autoplay video, and more.
Deep scan
Opt-in DevTools-Protocol scan for exact transferred bytes and real unused JavaScript & CSS.
Want the how-to? Read our guide to sustainable web design →
How it works
Measure
PageLens reads the transferred bytes of every resource on the page using the browser’s Performance API.
Estimate
Those bytes feed CO2.js to estimate emissions, adjusted for whether the host runs on green energy.
Score & advise
The result becomes an A–F Eco Score with a prioritized, plain-language list of what to fix first.
PageLens gives an actionable estimate, not an exact measurement. It’s transparent about its methodology and clearly flags any figure it has to approximate.
Frequently asked questions
What is PageLens?
PageLens is a free Chrome extension that estimates the carbon footprint of any web page and turns it into an actionable A–F Eco Score, with concrete recommendations to make the page lighter.
How does PageLens estimate CO₂ emissions?
It measures the bytes transferred when a page loads and applies CO2.js (the Sustainable Web Design model) from The Green Web Foundation, adjusting the estimate for whether the site is hosted on green energy.
How is the Eco Score calculated?
The Eco Score is a 0–100 rating, graded A–F, that blends four factors: carbon per view (40%), page weight (30%), green hosting (15%) and best practices (15%).
Is PageLens free?
Yes. PageLens is completely free to use and open about how its score is calculated.
Does PageLens collect my data?
No. PageLens analyzes the current page locally in your browser. Only the site’s hostname is sent to The Green Web Foundation to check for green hosting. There is no tracking, no analytics, and no account required.
Is the carbon estimate exact?
No — it is an actionable estimate, not a precise measurement. PageLens is transparent about its methodology and clearly flags any figure it has to approximate, such as cross-origin resources without timing data.
How do I send feedback or report a problem?
Email support@iamjarl.com — or use “Send feedback” at the bottom of the PageLens popup, which fills in your version for you. Every message is read. If you would rather report it in public, GitHub issues are open too.
Make your web lighter
PageLens gives you an Eco Score for the page you’re on in one click.
Free