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https://nejm.org

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
90
GRADE
A
FIX
2
REVIEW
2
PASS
11
INFO
2

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

Mobile Desktop
67
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.

2.03 s

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

4.28 s

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

658 ms

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

0.003

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

2.55 s

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

4.69 s

Page Load Progression

391 ms
781 ms
1.2 s
1.6 s
2.0 s
2.3 s
2.7 s
3.1 s
Checks
17
11 PASS 2 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 (530.5 KiB of 530.6 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
JS Execution Cost
Action
1314ms total JS execution
REVIEW
1314ms total JS execution
Warning::
https://www.nejm.org/cdn-cgi/challenge-platform/h/...: 1067ms CPU time
Info::
Unattributable: 153ms CPU time
Info::
https://www.nejm.org/: 95ms CPU time
Warning::
Third-party scripts: 1314ms (100% of total)

Main Thread Breakdown

Script Evaluation 79% Other 14%
ScriptTotalScriptingParse/CompileParty
https://www.nejm.org/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=9efeafb87da803711067ms1023ms16ms3rd
Unattributable153ms5ms0ms3rd
https://www.nejm.org/95ms16ms2ms3rd
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
531 KB transferred, 24 requests
PASS
531 KB transferred, 24 requests
Info::
Page weighs 946 KB (531 KB transferred)
Info::
24 HTTP requests
Info::
Estimated 0.11 g CO2 per page load
531 KB / 2.4 MB budget
531 KB transferred
24 requests
0.11 g CO2 per page load
Other 316.7 KiB 60%
HTML 100.9 KiB 19%
JavaScript 95.8 KiB 18%
Images 9.2 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+
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=9efeafb87da8037172 KB—✓3rd
https://static.cloudflareinsights.com/beacon.min.js/vcd15cbe7772f49c399c6a5babf22c12417176891760157 KB—✓3rd
blob:https://www.nejm.org/6ce8ce78-25d9-4cc0-8482-be49ee88327d0 KB—✓3rd
https://challenges.cloudflare.com/turnstile/v0/b/0b8fb825cb67/api.js?onload=cFRiY3&render=explicit17 KB—✓3rd
blob:https://www.nejm.org/2304df04-2c2b-46f0-a2a6-3c5b0b29e06d-0 KB—✓3rd
blob:https://challenges.cloudflare.com/168a3396-37b9-41f8-844c-cfdc90e6a5a80 KB—✓3rd
blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43-0 KB—✓3rd
blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43-0 KB—✓3rd
blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43-0 KB—✓3rd
blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43-0 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 · 531 KB · 0 KB savings available
PASS
24 resources · 531 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 531 KB
Warning::
22 third-party resources (100% of weight)
Info::
1 resources over 200KB
24 resources · 530.6 KiB · 22 third-party Within 1MB page-weight target
Other 60% · 318.4 KiB
Document 20% · 107.2 KiB
JavaScript 18% · 95.8 KiB
Image 2% · 9.2 KiB
A+
Render-Blocking Resources
No render-blocking resources detected
PASS
No render-blocking resources detected
Info::
No render-blocking resources detected in <head>
A+
Third-Party Resources
No third-party resources detected
PASS
No third-party resources detected
Network Waterfall
24 requests over 2602ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s FCP 2.0 s LCP 4.3 shttps://nejm.org// https://nejm.org/ — 301 — 83 B — 302 ms — h2https://www.nejm.org/www.nejm.org/ https://www.nejm.org/ — 307 — 58 B — 62 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 — 6.6 KiB — 30 ms — h3https://www.nejm.org/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=9efeafb87da80371www.nejm.org/cdn-cgi/challenge-plat... https://www.nejm.org/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=9efeafb87da80371 — 200 — 71.6 KiB — 88 ms — h3https://static.cloudflareinsights.com/beacon.min.js/vcd15cbe7772f49c399c6a5babf22c1241717689176015static.cloudflareinsights.com/beaco... https://static.cloudflareinsights.com/beacon.min.js/vcd15cbe7772f49c399c6a5babf22c1241717689176015 — 200 — 6.9 KiB — 95 ms — h2blob:https://www.nejm.org/6ce8ce78-25d9-4cc0-8482-be49ee88327dwww.nejm.org/6ce8ce78-25d9-4cc0-848... blob:https://www.nejm.org/6ce8ce78-25d9-4cc0-8482-be49ee88327d — -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 — 67 ms — h3https://www.nejm.org/favicon.icowww.nejm.org/favicon.ico https://www.nejm.org/favicon.ico — 403 — 7.6 KiB — 36 ms — h3https://www.nejm.org/cdn-cgi/rum?www.nejm.org/cdn-cgi/rum? https://www.nejm.org/cdn-cgi/rum? — 204 — 139 B — 31 ms — h3https://www.nejm.org/favicon.icowww.nejm.org/favicon.ico https://www.nejm.org/favicon.ico — 403 — 6.2 KiB — 47 ms — h3https://www.nejm.org/cdn-cgi/challenge-platform/h/b/flow/ov1/597893741:1776795215:vX6DMo7H36ToU6CK3GVGs0lXKjzgVqdLcuBarjY5DlI/9efeafb87da80371/2JHzQeOGlCTRBFi6MnPeZNOVSjtYwscwouYLgYMVFYw-1776798601-1.2.1.1-.sbNIWzbxC2GXhTYdB4ZEGtICUi6HGRGSPzhXVHDzl8_7mECt8YkpgNCwOhpjDb2www.nejm.org/cdn-cgi/challenge-plat... https://www.nejm.org/cdn-cgi/challenge-platform/h/b/flow/ov1/597893741:1776795215:vX6DMo7H36ToU6CK3GVGs0lXKjzgVqdLcuBarjY5DlI/9efeafb87da80371/2JHzQeOGlCTRBFi6MnPeZNOVSjtYwscwouYLgYMVFYw-1776798601-1.2.1.1-.sbNIWzbxC2GXhTYdB4ZEGtICUi6HGRGSPzhXVHDzl8_7mECt8YkpgNCwOhpjDb2 — 200 — 13.5 KiB — 53 ms — h3blob:https://www.nejm.org/2304df04-2c2b-46f0-a2a6-3c5b0b29e06dwww.nejm.org/2304df04-2c2b-46f0-a2a... blob:https://www.nejm.org/2304df04-2c2b-46f0-a2a6-3c5b0b29e06d — 200 — -1 B — 35 ms — blobhttps://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/turnstile/f/ov2/av0/rch/ogqxj/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/ogqxj/0x4AAAAAAADnPIDROrmt1Wwj/light/fbE/new/normal?lang=auto — 200 — 94.3 KiB — 102 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 — 21 ms — h3blob:https://challenges.cloudflare.com/168a3396-37b9-41f8-844c-cfdc90e6a5a8challenges.cloudflare.com/168a3396-... blob:https://challenges.cloudflare.com/168a3396-37b9-41f8-844c-cfdc90e6a5a8 — -1 — 0 B — 0 ms — https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/flow/ov1/2588405380:1776795216:AJWrEkDQ8dUubMe8zqJ3LDqGsZyer622-ACqEQQp-uI/9efeafbb4d545d26/YhIsHJInAQnYymnAZPjqQu_ZOnWIw8setejLjSMflR0-1776798601-1.2.1.1-DcwZnqm3mOs2trbNiKxy0FT9mCNJaZxyEf7iJfqvivZSzklRxn5VPR2pX7IlX_Ewchallenges.cloudflare.com/cdn-cgi/c... https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/flow/ov1/2588405380:1776795216:AJWrEkDQ8dUubMe8zqJ3LDqGsZyer622-ACqEQQp-uI/9efeafbb4d545d26/YhIsHJInAQnYymnAZPjqQu_ZOnWIw8setejLjSMflR0-1776798601-1.2.1.1-DcwZnqm3mOs2trbNiKxy0FT9mCNJaZxyEf7iJfqvivZSzklRxn5VPR2pX7IlX_Ew — 200 — 303.0 KiB — 156 ms — h3blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43challenges.cloudflare.com/0506164c-... blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43 — 200 — -1 B — 76 ms — blobhttps://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/d/9efeafbb4d545d26/1776798601791/lGDyio2CkhoqU13challenges.cloudflare.com/cdn-cgi/c... https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/d/9efeafbb4d545d26/1776798601791/lGDyio2CkhoqU13 — 200 — 1.4 KiB — 21 ms — h3blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43challenges.cloudflare.com/0506164c-... blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43 — 200 — -1 B — 11 ms — blobblob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43challenges.cloudflare.com/0506164c-... blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43 — 200 — -1 B — 46 ms — blobblob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43challenges.cloudflare.com/0506164c-... blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43 — 200 — -1 B — 50 ms — blobblob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43challenges.cloudflare.com/0506164c-... blob:https://challenges.cloudflare.com/0506164c-dd64-48a9-b816-72f9f35c1f43 — 200 — -1 B — 49 ms — blobhttps://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/pat/9efeafbb4d545d26/1776798601791/5a951290df4c7493733253b35ba702b9efe1e015ee3351fd7ba50c6f31ed53b6/N926o1z4g-5RYPBchallenges.cloudflare.com/cdn-cgi/c... https://challenges.cloudflare.com/cdn-cgi/challenge-platform/h/b/pat/9efeafbb4d545d26/1776798601791/5a951290df4c7493733253b35ba702b9efe1e015ee3351fd7ba50c6f31ed53b6/N926o1z4g-5RYPB — 401 — 1.7 KiB — 21 ms — h3
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 1314ms · 78KB · $17/mo
www.nejm.org
Other
Costly
Execution 1067ms
Transfer 72 KB
Monthly Cost $14/mo
Unattributable
Other
Optional
Execution 153ms
Transfer 0 KB
Monthly Cost $2/mo
www.nejm.org
Other
Optional
Execution 95ms
Transfer 7 KB
Monthly Cost $1/mo

These scripts may cost more than they're worth

  • www.nejm.org adds 1067ms and costs ~$14/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 1067ms 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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