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https://nejm.org

Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
90
GRADE
A
FIX
2
REVIEW
1
PASS
10
INFO
2

Performance-focused optimization plan with CWV assessment, top offenders, and time estimates

Mobile Desktop
95
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
90
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
96
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
45
SEO Measures basic SEO optimizations: meta tags, crawlability, link text, and mobile friendliness.

First Contentful Paint First Contentful Paint — how long until the browser renders the first piece of content. Under 1.8s is good.

811 ms

Largest Contentful Paint Largest Contentful Paint — how long until the largest visible element loads. Under 2.5s is good.

1.39 s

Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.

13 ms

Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.

0.001

Speed Index Speed Index — how quickly content is visually displayed during load. Under 3.4s is good.

851 ms

Time to Interactive Time to Interactive — how long until the page is fully interactive and responds to user input. Under 3.8s is good.

1.39 s

Page Load Progression

391 ms
782 ms
1.2 s
1.6 s
2.0 s
2.3 s
2.7 s
3.1 s
Checks
15
10 PASS 1 REVIEW 2 FIX
D
Third-Party Impact
Action
100% third-party, 0 ms blocking
FIX
100% third-party, 0 ms blocking
Warning::
Third-party code accounts for 100% of page weight (525.7 KiB of 525.8 KiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
HTTP Caching
Action
No cache headers
FIX
No cache headers
Warning::
No Cache-Control header found
Browsers will use heuristic caching, which can be unpredictable. Set explicit cache headers.

No Cache-Control header

Adding a Cache-Control header can significantly improve repeat-visit performance.

C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
526 KB transferred, 24 requests
PASS
526 KB transferred, 24 requests
Info::
Page weighs 938 KB (526 KB transferred)
Info::
24 HTTP requests
Info::
Estimated 0.11 g CO2 per page load
526 KB / 2.4 MB budget
526 KB transferred
24 requests
0.11 g CO2 per page load
Other 312.1 KiB 59%
HTML 101.5 KiB 19%
JavaScript 95.7 KiB 18%
Images 8.5 KiB 2%
Other 6.3 KiB 1%
Other 1.7 KiB 0%
0 2.4 MB 4.9 MB
Under budget
A+
Text Compression
All text resources are compressed
PASS
All text resources are compressed
Info::
All text resources are compressed
All text resources are properly compressed.
A
Image Optimization
3 images, 0 KB saveable
PASS
3 images, 0 KB saveable
Info::
All images are well-optimized
3 images 9 KB
0 oversized -0 KB
3 legacy format
0 missing dimensions CLS risk
A+
JS Execution Cost
251ms total JS execution
PASS
251ms total JS execution
Warning::
https://www.nejm.org/cdn-cgi/challenge-platform/h/...: 251ms CPU time
Warning::
Third-party scripts: 251ms (100% of total)

Main Thread Breakdown

Script Evaluation 79% Other 13% Script Parsing & Compilation 4%
ScriptTotalScriptingParse/CompileParty
https://www.nejm.org/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=9efeb00bffcbf135251ms238ms4ms3rd
A+
Font Loading
No web fonts (system fonts)
PASS
No web fonts (system fonts)
Info::
No web fonts loaded — system fonts are fastest
No web fonts loaded — system fonts are optimal.
A+
JS Bundles
11 scripts, 0 KB unused
PASS
11 scripts, 0 KB unused
0 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.nejm.org/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=9efeb00bffcbf13571 KB—✓3rd
https://static.cloudflareinsights.com/beacon.min.js/vcd15cbe7772f49c399c6a5babf22c12417176891760157 KB—✓3rd
blob:https://www.nejm.org/3c08babb-d3df-4fb4-b864-6948031ed93b0 KB—✓3rd
https://challenges.cloudflare.com/turnstile/v0/b/0b8fb825cb67/api.js?onload=cFRiY3&render=explicit17 KB—✓3rd
blob:https://www.nejm.org/9f764053-bb54-4bb3-bd4f-67b829be1b8a-0 KB—✓3rd
blob:https://challenges.cloudflare.com/87c09922-8884-42bd-87d8-46a2e692578e0 KB—✓3rd
blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56-0 KB—✓3rd
blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56-0 KB—✓3rd
blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56-0 KB—✓3rd
blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56-0 KB—✓3rd
A+
Resource Caching
All resources properly cached
PASS
All resources properly cached
Info::
No caching issues found
All static resources have appropriate caching headers.
A+
Critical Rendering Path
No render-blocking resources
PASS
No render-blocking resources
Info::
No render-blocking resources detected
A+
Resource Hints
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
A
Page Weight Inventory
24 resources · 526 KB · 0 KB savings available
PASS
24 resources · 526 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 526 KB
Warning::
22 third-party resources (100% of weight)
Info::
1 resources over 200KB
24 resources · 525.8 KiB · 22 third-party Within 1MB page-weight target
Other 60% · 313.8 KiB
Document 20% · 107.7 KiB
JavaScript 18% · 95.7 KiB
Image 2% · 8.5 KiB
Network Waterfall
24 requests over 1635ms
INFO
0 ms 500 ms 1.0 s 1.5 s FCP 811 ms LCP 1.4 shttps://nejm.org// https://nejm.org/ — 301 — 83 B — 306 ms — h2https://www.nejm.org/www.nejm.org/ https://www.nejm.org/ — 307 — 58 B — 83 ms — http/1.1https://nejm.org// https://nejm.org/ — 301 — 0 B — 1 ms — h2https://www.nejm.org/www.nejm.org/ https://www.nejm.org/ — 403 — 6.5 KiB — 34 ms — h3https://www.nejm.org/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=9efeb00bffcbf135www.nejm.org/cdn-cgi/challenge-plat... https://www.nejm.org/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=9efeb00bffcbf135 — 200 — 71.5 KiB — 70 ms — h3https://static.cloudflareinsights.com/beacon.min.js/vcd15cbe7772f49c399c6a5babf22c1241717689176015static.cloudflareinsights.com/beaco... https://static.cloudflareinsights.com/beacon.min.js/vcd15cbe7772f49c399c6a5babf22c1241717689176015 — 200 — 6.9 KiB — 66 ms — h2blob:https://www.nejm.org/3c08babb-d3df-4fb4-b864-6948031ed93bwww.nejm.org/3c08babb-d3df-4fb4-b86... blob:https://www.nejm.org/3c08babb-d3df-4fb4-b864-6948031ed93b — -1 — 0 B — 0 ms — https://challenges.cloudflare.com/turnstile/v0/b/0b8fb825cb67/api.js?onload=cFRiY3&render=explicitchallenges.cloudflare.com/turnstile... https://challenges.cloudflare.com/turnstile/v0/b/0b8fb825cb67/api.js?onload=cFRiY3&render=explicit — 200 — 17.4 KiB — 63 ms — h3https://www.nejm.org/favicon.icowww.nejm.org/favicon.ico https://www.nejm.org/favicon.ico — 403 — 7.5 KiB — 32 ms — h3https://www.nejm.org/cdn-cgi/rum?www.nejm.org/cdn-cgi/rum? https://www.nejm.org/cdn-cgi/rum? — 204 — 139 B — 26 ms — h3https://www.nejm.org/favicon.icowww.nejm.org/favicon.ico https://www.nejm.org/favicon.ico — 403 — 6.2 KiB — 35 ms — h3https://www.nejm.org/cdn-cgi/challenge-platform/h/b/flow/ov1/597893741:1776795215:vX6DMo7H36ToU6CK3GVGs0lXKjzgVqdLcuBarjY5DlI/9efeb00bffcbf135/Q4h.mJZB5cZ7RFOyMaZTwOWc7ppP6ibPSzFkuuA0cqw-1776798614-1.2.1.1-GtmlTwydkuKp4.PiCIpEBomVre2IxYeYyE_CPsEh7LyrOmh5T..53SFW425XQJUlwww.nejm.org/cdn-cgi/challenge-plat... https://www.nejm.org/cdn-cgi/challenge-platform/h/b/flow/ov1/597893741:1776795215:vX6DMo7H36ToU6CK3GVGs0lXKjzgVqdLcuBarjY5DlI/9efeb00bffcbf135/Q4h.mJZB5cZ7RFOyMaZTwOWc7ppP6ibPSzFkuuA0cqw-1776798614-1.2.1.1-GtmlTwydkuKp4.PiCIpEBomVre2IxYeYyE_CPsEh7LyrOmh5T..53SFW425XQJUl — 200 — 13.5 KiB — 58 ms — h3blob:https://www.nejm.org/9f764053-bb54-4bb3-bd4f-67b829be1b8awww.nejm.org/9f764053-bb54-4bb3-bd4... blob:https://www.nejm.org/9f764053-bb54-4bb3-bd4f-67b829be1b8a — 200 — -1 B — 26 ms — blobhttps://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/turnstile/f/ov2/av0/rch/1jiwi/0x4AAAAAAADnPIDROrmt1Wwj/light/fbE/new/normal?lang=autochallenges.cloudflare.com/cdn-cgi/c... https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/turnstile/f/ov2/av0/rch/1jiwi/0x4AAAAAAADnPIDROrmt1Wwj/light/fbE/new/normal?lang=auto — 200 — 95.0 KiB — 108 ms — h3https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/cmg/1challenges.cloudflare.com/cdn-cgi/c... https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/cmg/1 — 200 — 208 B — 25 ms — h3blob:https://challenges.cloudflare.com/87c09922-8884-42bd-87d8-46a2e692578echallenges.cloudflare.com/87c09922-... blob:https://challenges.cloudflare.com/87c09922-8884-42bd-87d8-46a2e692578e — -1 — 0 B — 0 ms — https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/flow/ov1/2588405380:1776795216:AJWrEkDQ8dUubMe8zqJ3LDqGsZyer622-ACqEQQp-uI/9efeb00ecc312a7c/Fnvev8ZY8W5ficwpys4_tuKEQ353bKjvyoKF4Dx3FtE-1776798614-1.2.1.1-eG8inETJ.A8t8bUsm3PnvPGcHZ6ujn2z6T00xZq9pGwHR0JfG93qtGk6xhnyXslschallenges.cloudflare.com/cdn-cgi/c... https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/flow/ov1/2588405380:1776795216:AJWrEkDQ8dUubMe8zqJ3LDqGsZyer622-ACqEQQp-uI/9efeb00ecc312a7c/Fnvev8ZY8W5ficwpys4_tuKEQ353bKjvyoKF4Dx3FtE-1776798614-1.2.1.1-eG8inETJ.A8t8bUsm3PnvPGcHZ6ujn2z6T00xZq9pGwHR0JfG93qtGk6xhnyXsls — 200 — 298.4 KiB — 192 ms — h3blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56challenges.cloudflare.com/f5bf3f4a-... blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56 — 200 — -1 B — 18 ms — blobblob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56challenges.cloudflare.com/f5bf3f4a-... blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56 — 200 — -1 B — 16 ms — blobhttps://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/d/9efeb00ecc312a7c/1776798615155/zkhHc2olHPDiTHAchallenges.cloudflare.com/cdn-cgi/c... https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/d/9efeb00ecc312a7c/1776798615155/zkhHc2olHPDiTHA — 200 — 798 B — 22 ms — h3https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/pat/9efeb00ecc312a7c/1776798615155/d51652d0108203b39df8c6e0d2148aef0772ad13a0b829726393bdab2dd897aa/XcAONdPPOuO8VAachallenges.cloudflare.com/cdn-cgi/c... https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/pat/9efeb00ecc312a7c/1776798615155/d51652d0108203b39df8c6e0d2148aef0772ad13a0b829726393bdab2dd897aa/XcAONdPPOuO8VAa — 401 — 1.7 KiB — 22 ms — h3blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56challenges.cloudflare.com/f5bf3f4a-... blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56 — 200 — -1 B — 19 ms — blobblob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56challenges.cloudflare.com/f5bf3f4a-... blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56 — 200 — -1 B — 21 ms — blobblob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56challenges.cloudflare.com/f5bf3f4a-... blob:https://challenges.cloudflare.com/f5bf3f4a-e866-49a8-ad6c-3538cabb1e56 — 200 — -1 B — 21 ms — blob
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
100% of JavaScript execution is third-party
First-party Third-party 251ms · 71KB · $3/mo
www.nejm.org
Other
Costly
Execution 251ms
Transfer 71 KB
Monthly Cost $3/mo

These scripts may cost more than they're worth

  • www.nejm.org adds 251ms and costs ~$3/month

100% of JavaScript execution time is spent on third-party scripts. Consider auditing which scripts are essential.

Why this matters

When third-party JS execution time exceeds your own, performance gains from frontend work are capped by code you don't own.

Learn more ▾

Every millisecond of third-party JS competes with your own for main-thread time. If their share is bigger than yours, optimization on your code base barely moves the needle. Audit, defer, or remove third-parties before further frontend optimization. Use Lighthouse's third-party audit to identify the worst offenders.

Source: web.dev

www.nejm.org takes 251ms of CPU time. Consider loading it asynchronously or replacing it with a lighter alternative.

Why this matters

This script has high main-thread execution time — optimize hot paths or defer.

Source: web.dev

How third-party costs are calculated

All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.

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