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Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
83
GRADE
B
FIX
2
REVIEW
5
PASS
8
INFO
2

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

Mobile Desktop
59
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
89
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
100
Best Practices Checks for modern web development best practices including HTTPS, no console errors, and secure JavaScript.
92
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.

2.72 s

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

13.26 s

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

369 ms

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

0.000

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

4.76 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.

13.46 s

Page Load Progression

375 ms
750 ms
1.1 s
1.5 s
1.9 s
2.2 s
2.6 s
3.0 s
Checks
17
8 PASS 5 REVIEW 2 FIX
D
Page Weight Budget
Action
2.6 MB transferred, 26 requests
FIX
2.6 MB transferred, 26 requests
Warning::
Page weighs 3.5 MB (2.6 MB transferred)
Warning::
Images are 2.0 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 2.0 MB
Info::
26 HTTP requests
Info::
Estimated 0.54 g CO2 per page load
2.6 MB / 2.4 MB budget
2.6 MB transferred
26 requests
0.54 g CO2 per page load
Images 2.0 MiB 77%
JavaScript 396.5 KiB 15%
Fonts 156.2 KiB 6%
HTML 20.6 KiB 1%
CSS 17.4 KiB 1%
Other 1.5 KiB 0%
Other 543 B 0%
Other 307 B 0%
0 2.4 MB 4.9 MB
Over budget

Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.

Why this matters

Image bandwidth is high — modern formats (WebP/AVIF) and resizing typically cut it 50%+.

Source: web.dev

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
Image Optimization
Action
10 images, 0 KB saveable
REVIEW
10 images, 0 KB saveable
Warning::
https://fas.org/wp-content/themes/fas/assets/image... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://fas.org/wp-content/uploads/2023/02/homepag... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
10 images 2.0 MB
0 oversized -0 KB
10 legacy format
2 missing dimensions CLS risk

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

Set explicit width and height to prevent CLS.

Why this matters

Image without explicit width/height — browser can't reserve space; CLS jumps when image loads.

Source: web.dev / Core Web Vitals

C
JS Execution Cost
Action
1101ms total JS execution
REVIEW
1101ms total JS execution
Warning::
Unattributable: 269ms CPU time
Warning::
https://fas.org/: 267ms CPU time
Info::
https://www.googletagmanager.com/gtag/js?id=G-ECXR...: 217ms CPU time
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-N6T...: 201ms CPU time
Info::
https://fas.org/wp-content/themes/fas/assets/dist/...: 147ms CPU time
Warning::
Third-party scripts: 688ms (62% of total)

Main Thread Breakdown

Script Evaluation 45% Other 20% Style & Layout 16% Script Parsing & Compilation 13% Parse HTML & CSS 4%
ScriptTotalScriptingParse/CompileParty
Unattributable269ms75ms0ms3rd
https://fas.org/267ms10ms3ms1st
https://www.googletagmanager.com/gtag/js?id=G-ECXRQ9RTQS&cx=c&gtm=4e64h1h1217ms158ms57ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-N6TJX7F201ms151ms44ms3rd
https://fas.org/wp-content/themes/fas/assets/dist/main.js?ver=1775857560147ms88ms46ms1st
C
JS Bundles
Action
6 scripts, 226 KB unused
REVIEW
6 scripts, 226 KB unused
Warning::
https://fas.org/wp-content/themes/fas/assets/dist/...: 97 KB unused (85%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=G-ECXR...: 65 KB unused (42%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-N6T...: 64 KB unused (53%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 226 KB
226 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://fas.org/wp-content/themes/fas/assets/dist/main.js?ver=1775857560115 KB97 KB (85%)✓1st
https://www.googletagmanager.com/gtag/js?id=G-ECXRQ9RTQS&cx=c&gtm=4e64h1h1153 KB65 KB (42%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-N6TJX7F120 KB64 KB (53%)✓3rd
blob:https://fas.org/84aa91a0-02a9-49a4-9c24-cb528b0154e8-0 KB—✓3rd
https://fas.org/wp-includes/js/wp-emoji-release.min.js?ver=6.95 KB—✓1st
https://analytics.ahrefs.com/analytics.js3 KB—✓3rd

Consider code splitting or tree shaking to reduce unused code.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

Consider code splitting or tree shaking to reduce unused code.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

Consider code splitting or tree shaking to reduce unused code.

Why this matters

This bundle has high unused code — code-split or tree-shake to ship only what executes.

Source: web.dev / Lighthouse coverage

C
Page Weight Inventory
Action
26 resources · 2.6 MB · 226 KB savings available
REVIEW
26 resources · 2.6 MB · 226 KB savings available
Warning::
Page weight 1.6 MB over 1MB target
Got: 2.6 MB Expected: ≤ 1 MB
Info::
~226 KB of savings available
Info::
6 third-party resources (11% of weight)
Info::
5 resources over 200KB
26 resources · 2.6 MiB · 6 third-party 1.6 MiB over 1MB target
Image 77% · 2.0 MiB
JavaScript 15% · 396.5 KiB
Font 6% · 156.2 KiB
Document 1% · 20.6 KiB
CSS 1% · 17.4 KiB
Other 0% · 850 B

~225.9 KiB of savings available

Remove unused JavaScript: 225.9 KiB
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Third-Party Impact
11% third-party, 0 ms blocking
PASS
11% third-party, 0 ms blocking
Info::
Third-party code accounts for 11% of page weight (277.3 KiB of 2.6 MiB)
Info::
Third-party blocking time is low (0 ms)
89%
First-party Third-party
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+
Font Loading
4 fonts (156 KB)
PASS
4 fonts (156 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

156 KB total

Render-blocking

0

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s FCP 2.7 s LCP 13.3 shttps://fas.org/wp-content/themes/fas/assets/fonts/StabilGrotesk-Light.woff2StabilGrotesk-Light.woff2 https://fas.org/wp-content/themes/fas/assets/fonts/StabilGrotesk-Light.woff2 — 43.2 KiB — 60 ms — font-display: swaphttps://fas.org/wp-content/themes/fas/assets/fonts/StabilGrotesk-Bold.woff2StabilGrotesk-Bold.woff2 https://fas.org/wp-content/themes/fas/assets/fonts/StabilGrotesk-Bold.woff2 — 43.3 KiB — 63 ms — font-display: swaphttps://fas.org/wp-content/themes/fas/assets/fonts/PPFraktionMono-Regular.woff2PPFraktionMono-Regular.... https://fas.org/wp-content/themes/fas/assets/fonts/PPFraktionMono-Regular.woff2 — 34.4 KiB — 65 ms — font-display: swaphttps://fas.org/wp-content/themes/fas/assets/fonts/PPFraktionMono-Bold.woff2PPFraktionMono-Bold.woff2 https://fas.org/wp-content/themes/fas/assets/fonts/PPFraktionMono-Bold.woff2 — 35.2 KiB — 67 ms — font-display: swap
StabilGrotesk-Light.woff2 woff2 swap
Size 43 KB
Load time 60 ms
Start 344 ms
Risk FOUT — text flashes from fallback to web font
StabilGrotesk-Bold.woff2 woff2 swap
Size 43 KB
Load time 63 ms
Start 345 ms
Risk FOUT — text flashes from fallback to web font
PPFraktionMono-Regular.... woff2 swap
Size 34 KB
Load time 65 ms
Start 345 ms
Risk FOUT — text flashes from fallback to web font
PPFraktionMono-Bold.woff2 woff2 swap
Size 35 KB
Load time 67 ms
Start 345 ms
Risk FOUT — text flashes from fallback to web font
Optimization checklist
  • Preload critical fonts (priority=high)
  • Use woff2 format for all fonts
  • Set font-display to swap, optional, or fallback
  • Subset large fonts (≤100 KB each)
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
1 hints, 0 missing preconnects
PASS
1 hints, 0 missing preconnects
Info::
Page uses 1 resource hint(s)

Current Resource Hints

preconnect
—
preload
1
dns-prefetch
—
prefetch
—

1 resource hints configured

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
26 requests over 607ms
INFO
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s FCP 2.7 s LCP 13.3 shttps://fas.org// https://fas.org/ — 200 — 20.6 KiB — 142 ms — h2https://fas.org/wp-content/plugins/tablepress/css/build/default.css?ver=3.2.6/wp-content/plugins/tablepress/css/... https://fas.org/wp-content/plugins/tablepress/css/build/default.css?ver=3.2.6 — 200 — 1.9 KiB — 37 ms — h2https://fas.org/wp-content/themes/fas/assets/dist/main.js?ver=1775857560/wp-content/themes/fas/assets/dist/... https://fas.org/wp-content/themes/fas/assets/dist/main.js?ver=1775857560 — 200 — 114.8 KiB — 105 ms — h2https://fas.org/wp-content/themes/fas/assets/dist/main.css?version=1776370165/wp-content/themes/fas/assets/dist/... https://fas.org/wp-content/themes/fas/assets/dist/main.css?version=1776370165 — 200 — 15.5 KiB — 39 ms — h2https://fas.org/wp-content/uploads/2023/02/homepage-hero-722x697.jpg/wp-content/uploads/2023/02/homepag... https://fas.org/wp-content/uploads/2023/02/homepage-hero-722x697.jpg — 200 — 48.0 KiB — 118 ms — h2https://fas.org/wp-content/uploads/2026/03/0316-state-energy-722x376.png/wp-content/uploads/2026/03/0316-st... https://fas.org/wp-content/uploads/2026/03/0316-state-energy-722x376.png — 200 — 311.6 KiB — 153 ms — h2https://fas.org/wp-content/uploads/2023/02/emerging-technology-722x722.png/wp-content/uploads/2023/02/emergin... https://fas.org/wp-content/uploads/2023/02/emerging-technology-722x722.png — 200 — 315.2 KiB — 47 ms — h2https://fas.org/wp-content/uploads/2023/02/climate-722x722.png/wp-content/uploads/2023/02/climate... https://fas.org/wp-content/uploads/2023/02/climate-722x722.png — 200 — 373.5 KiB — 71 ms — h2https://fas.org/wp-content/uploads/2023/11/01-GLOBE-722x480.png/wp-content/uploads/2023/11/01-GLOB... https://fas.org/wp-content/uploads/2023/11/01-GLOBE-722x480.png — 200 — 178.3 KiB — 80 ms — h2https://fas.org/wp-content/uploads/2023/02/energy-722x722.png/wp-content/uploads/2023/02/energy-... https://fas.org/wp-content/uploads/2023/02/energy-722x722.png — 200 — 205.1 KiB — 88 ms — h2https://fas.org/wp-content/uploads/2023/01/pedro-lastra-Nyvq2juw4_o-unsplash-722x444.jpg/wp-content/uploads/2023/01/pedro-l... https://fas.org/wp-content/uploads/2023/01/pedro-lastra-Nyvq2juw4_o-unsplash-722x444.jpg — 200 — 90.1 KiB — 91 ms — h2https://fas.org/wp-content/uploads/2024/06/government-capacity-722x722.png/wp-content/uploads/2024/06/governm... https://fas.org/wp-content/uploads/2024/06/government-capacity-722x722.png — 200 — 281.9 KiB — 103 ms — h2https://www.googletagmanager.com/gtm.js?id=GTM-N6TJX7Fwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-N6TJX7F — 200 — 120.3 KiB — 74 ms — h2https://fas.org/wp-content/themes/fas/assets/images/day-one-block-background-mobile.png/wp-content/themes/fas/assets/image... https://fas.org/wp-content/themes/fas/assets/images/day-one-block-background-mobile.png — 200 — 107.4 KiB — 106 ms — h2https://fas.org/wp-content/themes/fas/assets/images/day-one-block-background-desktop.png/wp-content/themes/fas/assets/image... https://fas.org/wp-content/themes/fas/assets/images/day-one-block-background-desktop.png — 200 — 117.7 KiB — 111 ms — h2blob:https://fas.org/84aa91a0-02a9-49a4-9c24-cb528b0154e8fas.org/84aa91a0-02a9-49a4-9c24-cb5... blob:https://fas.org/84aa91a0-02a9-49a4-9c24-cb528b0154e8 — 200 — -1 B — 80 ms — blobhttps://fas.org/wp-content/themes/fas/assets/fonts/StabilGrotesk-Light.woff2/wp-content/themes/fas/assets/fonts... https://fas.org/wp-content/themes/fas/assets/fonts/StabilGrotesk-Light.woff2 — 200 — 43.2 KiB — 60 ms — h2https://fas.org/wp-content/themes/fas/assets/fonts/StabilGrotesk-Bold.woff2/wp-content/themes/fas/assets/fonts... https://fas.org/wp-content/themes/fas/assets/fonts/StabilGrotesk-Bold.woff2 — 200 — 43.3 KiB — 63 ms — h2https://fas.org/wp-content/themes/fas/assets/fonts/PPFraktionMono-Regular.woff2/wp-content/themes/fas/assets/fonts... https://fas.org/wp-content/themes/fas/assets/fonts/PPFraktionMono-Regular.woff2 — 200 — 34.4 KiB — 65 ms — h2https://fas.org/wp-content/themes/fas/assets/fonts/PPFraktionMono-Bold.woff2/wp-content/themes/fas/assets/fonts... https://fas.org/wp-content/themes/fas/assets/fonts/PPFraktionMono-Bold.woff2 — 200 — 35.2 KiB — 67 ms — h2https://fas.org/wp-includes/js/wp-emoji-release.min.js?ver=6.9/wp-includes/js/wp-emoji-release.mi... https://fas.org/wp-includes/js/wp-emoji-release.min.js?ver=6.9 — 200 — 5.2 KiB — 38 ms — h2https://www.googletagmanager.com/gtag/js?id=G-ECXRQ9RTQS&cx=c&gtm=4e64h1h1www.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-ECXRQ9RTQS&cx=c&gtm=4e64h1h1 — 200 — 153.2 KiB — 59 ms — h2https://analytics.ahrefs.com/analytics.jsanalytics.ahrefs.com/analytics.js https://analytics.ahrefs.com/analytics.js — 200 — 3.0 KiB — 37 ms — h3https://analytics.ahrefs.com/api/eventanalytics.ahrefs.com/api/event https://analytics.ahrefs.com/api/event — 200 — 307 B — 29 ms — h3https://www.google-analytics.com/g/collect?v=2&tid=G-ECXRQ9RTQS&gtm=45je64h1h1v889303355z8889589459za20gzb889589459zd889589459&_p=1776804843429&gcd=13l3l3l3l1l1&npa=0&dma=0&are=1&cid=1705254340.1776804844&frm=0&pscdl=noapi&rcb=5&sr=412x823&uaa=&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uam=moto%20g%20power%20(2022)&uamb=1&uap=Android&uapv=11.0&uaw=0&ul=en-us&_s=1&tag_exp=0~115938466~115938469~117266400~118463262&sid=1776804843&sct=1&seg=0&dl=https%3A%2F%2Ffas.org%2F&dt=Home%20-%20Federation%20of%20American%20Scientists&en=page_view&_fv=1&_nsi=1&_ss=1&ep.published_date=null&ep.null=null&tfd=565www.google-analytics.com/g/collect?... https://www.google-analytics.com/g/collect?v=2&tid=G-ECXRQ9RTQS&gtm=45je64h1h1v889303355z8889589459za20gzb889589459zd889589459&_p=1776804843429&gcd=13l3l3l3l1l1&npa=0&dma=0&are=1&cid=1705254340.1776804844&frm=0&pscdl=noapi&rcb=5&sr=412x823&uaa=&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uam=moto%20g%20power%20(2022)&uamb=1&uap=Android&uapv=11.0&uaw=0&ul=en-us&_s=1&tag_exp=0~115938466~115938469~117266400~118463262&sid=1776804843&sct=1&seg=0&dl=https%3A%2F%2Ffas.org%2F&dt=Home%20-%20Federation%20of%20American%20Scientists&en=page_view&_fv=1&_nsi=1&_ss=1&ep.published_date=null&ep.null=null&tfd=565 — 204 — 543 B — 37 ms — h2https://fas.org/wp-content/themes/fas/assets/images/favicon.ico/wp-content/themes/fas/assets/image... https://fas.org/wp-content/themes/fas/assets/images/favicon.ico — 200 — 1.5 KiB — 36 ms — h2
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
62% of JavaScript execution is third-party
First-party Third-party 688ms · 274KB · $9/mo
Unattributable
Other
Costly
Execution 269ms
Transfer 0 KB
Monthly Cost $4/mo
Google Tag Manager
Tag Manager
Costly
Execution 217ms
Transfer 153 KB
Unused 42%
Monthly Cost $3/mo
Google Tag Manager
Tag Manager
Costly
Execution 201ms
Transfer 120 KB
Unused 53%
Monthly Cost $3/mo

These scripts may cost more than they're worth

  • Unattributable adds 269ms and costs ~$4/month
  • Google Tag Manager adds 217ms and costs ~$3/month
  • Google Tag Manager adds 201ms and costs ~$3/month

62% of JavaScript execution time comes from third-party scripts.

Why this matters

Third-party scripts (analytics, ads, social, A/B testing) often dominate execution time — every one is a perf-and-privacy tax.

Learn more ▾

Each third-party script is a black box: you don't control when it loads, what it executes, or how much it grows. They often account for a major share of total blocking time on average sites (HTTP Archive's Web Almanac documents the trend). Audit which ones you actually need, defer the rest, and use facade patterns (lite-youtube, lite-vimeo) for embedded media.

Source: web.dev / HTTP Archive Web Almanac

Unattributable takes 269ms 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

Google Tag Manager takes 217ms 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

Google Tag Manager takes 201ms 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

53% of Google Tag Manager's code is unused. The script may be loading features you don't use.

Why this matters

Bundle has high unused-code ratio — tree-shaking and route-splitting recover the wasted bytes.

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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