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Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
66
GRADE
D
FIX
4
REVIEW
2
PASS
7
INFO
2

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

Mobile Desktop
68
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.
100
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.

1.45 s

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

5.51 s

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

44 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.

2.08 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.

7.32 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
15
7 PASS 2 REVIEW 4 FIX
F
Page Weight Budget
Action
10.5 MB transferred, 71 requests
FIX
10.5 MB transferred, 71 requests
Critical::
Page weighs 10.9 MB (10.5 MB transferred)
Warning::
Images are 6.3 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 6.3 MB
Warning::
JavaScript is 3.4 MB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 3.4 MB
Info::
CSS is 386 KB — consider purging unused styles
Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.
Got: 386 KB
Info::
Fonts are 230 KB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 230 KB
Info::
71 HTTP requests
Info::
Estimated 2.2 g CO2 per page load
10.5 MB / 2.4 MB budget
10.5 MB transferred
71 requests
2.2 g CO2 per page load
Images 6.3 MiB 60%
JavaScript 3.4 MiB 32%
CSS 386.2 KiB 4%
Fonts 229.7 KiB 2%
HTML 174.2 KiB 2%
Other 39.8 KiB 0%
Other 1.4 KiB 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

Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.

Why this matters

JavaScript bundle is large — code-split routes and lazy-load off-screen components to defer.

Source: web.dev

Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.

Why this matters

CSS bundle is large — purge unused styles (PurgeCSS, Tailwind JIT) to reduce CSS payload.

Source: web.dev

Subset fonts to include only used characters, or switch to system font stacks.

Why this matters

Font payload is large — subset to used glyphs only, or fall back to system fonts (zero load time).

Source: web.dev font loading

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 (10.5 MiB of 10.5 MiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
F
JS Bundles
Action
6 scripts, 2.2 MB unused
FIX
6 scripts, 2.2 MB unused
Warning::
https://www.loc.gov/static/javascript/base.js: 2.1 MB unused (69%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.loc.gov/static/javascript/base.js: unminified — 1.2 MB could be saved
Warning::
https://www.loc.gov/static/js/lib/jquery-1.8.2.js: 103 KB unused (39%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.loc.gov/static/js/lib/jquery-1.8.2.js: unminified — 120 KB could be saved
Warning::
https://assets.adobedtm.com/dac62e20b491e735c6b56e...: 30 KB unused (37%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 2.2 MB
2295 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.loc.gov/static/javascript/base.js3120 KB2163 KB (69%)✗3rd
https://www.loc.gov/static/js/lib/jquery-1.8.2.js261 KB103 KB (39%)✗3rd
https://assets.adobedtm.com/dac62e20b491e735c6b56e64c39134d8ee93f9cf/satelliteLib-6b47f831c184878d7338d4683ecf773a17973bb9.js80 KB30 KB (37%)✓3rd
https://assets.adobedtm.com/extensions/EP31dbb9c60e404ba1aa6e746d49be6f29/AppMeasurement.min.js13 KB—✓3rd
https://assets.adobedtm.com/extensions/EP31dbb9c60e404ba1aa6e746d49be6f29/AppMeasurement_Module_ActivityMap.min.js2 KB—✓3rd
https://smon.loc.gov/id?d_visid_ver=5.5.0&d_fieldgroup=A&mcorgid=0D15148954E6C5100A4C98BC%40AdobeOrg&mid=19724936248218574191462401772914829762&ts=17763617549030 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

F
Page Weight Inventory
Action
71 resources · 10.5 MB · 2.2 MB savings available
FIX
71 resources · 10.5 MB · 2.2 MB savings available
Warning::
Page weight 9.5 MB over 1MB target
Got: 10.5 MB Expected: ≤ 1 MB
Info::
~2.2 MB of savings available
Warning::
70 third-party resources (100% of weight)
Info::
8 resources over 200KB
71 resources · 10.5 MiB · 70 third-party 9.5 MiB over 1MB target
Image 60% · 6.4 MiB
JavaScript 32% · 3.4 MiB
CSS 4% · 386.2 KiB
Font 2% · 229.7 KiB
Document 2% · 179.0 KiB
Other 0% · 1.9 KiB

~2.2 MiB of savings available

Remove unused JavaScript: 2.2 MiB
C
Image Optimization
Action
48 images, 0 KB saveable
REVIEW
48 images, 0 KB saveable
Warning::
https://www.loc.gov/static/home/images/your-librar... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/home/images/featured/ev... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/home/images/featured/co... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/home/images/featured/nb... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/home/images/your-librar... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/home/images/featured/pr... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/home/images/your-librar... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/home/images/featured/pr... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.loc.gov/static/portals/free-to-use/pub... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
48 images 6.2 MB
0 oversized -0 KB
43 legacy format
20 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

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

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

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

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

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

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

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

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

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

B
JS Execution Cost
791ms total JS execution
REVIEW
791ms total JS execution
Info::
https://www.loc.gov/static/javascript/base.js: 201ms CPU time
Info::
Unattributable: 190ms CPU time
Info::
https://www.loc.gov/: 178ms CPU time
Info::
https://www.loc.gov/static/js/lib/jquery-1.8.2.js: 141ms CPU time
Info::
https://assets.adobedtm.com/dac62e20b491e735c6b56e...: 81ms CPU time
Warning::
Third-party scripts: 791ms (100% of total)

Main Thread Breakdown

Script Evaluation 35% Other 27% Script Parsing & Compilation 16% Style & Layout 14% Parse HTML & CSS 4% Rendering 4%
ScriptTotalScriptingParse/CompileParty
https://www.loc.gov/static/javascript/base.js201ms79ms105ms3rd
Unattributable190ms4ms0ms3rd
https://www.loc.gov/178ms17ms6ms3rd
https://www.loc.gov/static/js/lib/jquery-1.8.2.js141ms109ms9ms3rd
https://assets.adobedtm.com/dac62e20b491e735c6b56e64c39134d8ee93f9cf/satelliteLib-6b47f831c184878d7338d4683ecf773a17973bb9.js81ms63ms11ms3rd
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 (230 KB)
PASS
4 fonts (230 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

230 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 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s FCP 1.4 s LCP 5.5 shttps://www.loc.gov/static/fonts/OpenSans-Regular.woff2OpenSans-Regular.woff2 https://www.loc.gov/static/fonts/OpenSans-Regular.woff2 — 46.0 KiB — 64 ms — font-display: swaphttps://www.loc.gov/static/fonts/OpenSans-Bold.woff2OpenSans-Bold.woff2 https://www.loc.gov/static/fonts/OpenSans-Bold.woff2 — 47.8 KiB — 45 ms — font-display: swaphttps://www.loc.gov/static/css/fa/fonts/fontawesome-webfont.woff2?v=4.6.3fontawesome-webfont.woff2 https://www.loc.gov/static/css/fa/fonts/fontawesome-webfont.woff2?v=4.6.3 — 72.6 KiB — 50 ms — font-display: swaphttps://www.loc.gov/static/fonts/RobotoSlab-Bold.woff2RobotoSlab-Bold.woff2 https://www.loc.gov/static/fonts/RobotoSlab-Bold.woff2 — 63.3 KiB — 47 ms — font-display: swap
OpenSans-Regular.woff2 woff2 swap
Size 46 KB
Load time 64 ms
Start 113 ms
Risk FOUT — text flashes from fallback to web font
OpenSans-Bold.woff2 woff2 swap
Size 48 KB
Load time 45 ms
Start 113 ms
Risk FOUT — text flashes from fallback to web font
fontawesome-webfont.woff2 unknown swap
Size 73 KB
Load time 50 ms
Start 113 ms
Risk FOUT — text flashes from fallback to web font
RobotoSlab-Bold.woff2 woff2 swap
Size 63 KB
Load time 47 ms
Start 114 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)

Fixing the unchecked items could save ~22 KB and ~44 ms

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+
Green Hosting
Whether the site is served from green-energy infrastructure
PASS

Green Hosting

This site is hosted on green energy infrastructure

Provider: Cloudflare

A
HTTP Caching
max-age=3600 (1 hour)
PASS
max-age=3600 (1 hour)
Info::
Cache-Control header is set
Got: no-transform, max-age=3600
Info::
Effective TTL: 1 hour (max-age=3600)
Info::
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control

no-transform, max-age=3600

DirectiveValueMeaning
no-transform—
max-age3600Cache for 1 hour
Effective TTL: 3600 seconds
Network Waterfall
71 requests over 1173ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s 5.0 s FCP 1.4 s LCP 5.5 shttps://loc.gov// https://loc.gov/ — 301 — 2.5 KiB — 67 ms — h2https://www.loc.gov/www.loc.gov/ https://www.loc.gov/ — 200 — 171.0 KiB — 39 ms — h2https://www.loc.gov/static/stylesheets/base.csswww.loc.gov/static/stylesheets/base... https://www.loc.gov/static/stylesheets/base.css — 200 — 386.2 KiB — 43 ms — h2https://www.loc.gov/static/fonts/OpenSans-Regular.woff2www.loc.gov/static/fonts/OpenSans-R... https://www.loc.gov/static/fonts/OpenSans-Regular.woff2 — 200 — 46.0 KiB — 64 ms — h2https://www.loc.gov/static/fonts/OpenSans-Bold.woff2www.loc.gov/static/fonts/OpenSans-B... https://www.loc.gov/static/fonts/OpenSans-Bold.woff2 — 200 — 47.8 KiB — 45 ms — h2https://www.loc.gov/static/css/fa/fonts/fontawesome-webfont.woff2?v=4.6.3www.loc.gov/static/css/fa/fonts/fon... https://www.loc.gov/static/css/fa/fonts/fontawesome-webfont.woff2?v=4.6.3 — 200 — 72.6 KiB — 50 ms — h2https://www.loc.gov/static/fonts/RobotoSlab-Bold.woff2www.loc.gov/static/fonts/RobotoSlab... https://www.loc.gov/static/fonts/RobotoSlab-Bold.woff2 — 200 — 63.3 KiB — 47 ms — h2https://assets.adobedtm.com/dac62e20b491e735c6b56e64c39134d8ee93f9cf/satelliteLib-6b47f831c184878d7338d4683ecf773a17973bb9.jsassets.adobedtm.com/dac62e20b491e73... https://assets.adobedtm.com/dac62e20b491e735c6b56e64c39134d8ee93f9cf/satelliteLib-6b47f831c184878d7338d4683ecf773a17973bb9.js — 200 — 80.3 KiB — 24 ms — h2https://www.loc.gov/static/js/lib/jquery-1.8.2.jswww.loc.gov/static/js/lib/jquery-1.... https://www.loc.gov/static/js/lib/jquery-1.8.2.js — 200 — 261.1 KiB — 61 ms — h2https://www.loc.gov/static/images/logo-loc-new-branding.svgwww.loc.gov/static/images/logo-loc-... https://www.loc.gov/static/images/logo-loc-new-branding.svg — 200 — 15.2 KiB — 42 ms — h2https://www.loc.gov/static/home/images/featured/nbf/NBF20261200x560.jpegwww.loc.gov/static/home/images/feat... https://www.loc.gov/static/home/images/featured/nbf/NBF20261200x560.jpeg — 200 — 1.5 MiB — 135 ms — h2https://dpm.demdex.net/id?d_visid_ver=5.5.0&d_fieldgroup=MC&d_rtbd=json&d_ver=2&d_orgid=0D15148954E6C5100A4C98BC%40AdobeOrg&d_nsid=0&ts=1776361754820dpm.demdex.net/id?d_visid_ver=5.5.0... https://dpm.demdex.net/id?d_visid_ver=5.5.0&d_fieldgroup=MC&d_rtbd=json&d_ver=2&d_orgid=0D15148954E6C5100A4C98BC%40AdobeOrg&d_nsid=0&ts=1776361754820 — 200 — 929 B — 34 ms — h2https://www.loc.gov/static/home/images/featured/collections/Gugusse1200x560.pngwww.loc.gov/static/home/images/feat... https://www.loc.gov/static/home/images/featured/collections/Gugusse1200x560.png — 200 — 1.5 MiB — 192 ms — h2https://www.loc.gov/static/home/images/featured/programs/2026SpringConcert_1200x560.jpgwww.loc.gov/static/home/images/feat... https://www.loc.gov/static/home/images/featured/programs/2026SpringConcert_1200x560.jpg — 200 — 181.5 KiB — 90 ms — 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https://www.loc.gov/static/images/copyright-gov.svg — 200 — 28.5 KiB — 60 ms — h2https://www.loc.gov/static/images/slick-left-arrow.svgwww.loc.gov/static/images/slick-lef... https://www.loc.gov/static/images/slick-left-arrow.svg — 200 — 3.7 KiB — 26 ms — h2https://www.loc.gov/static/images/slick-right-arrow.svgwww.loc.gov/static/images/slick-rig... https://www.loc.gov/static/images/slick-right-arrow.svg — 200 — 1.6 KiB — 22 ms — h2https://www.loc.gov/static/home/images/trending/video-screenshots/2025-staff-highlight_640x360.jpgwww.loc.gov/static/home/images/tren... https://www.loc.gov/static/home/images/trending/video-screenshots/2025-staff-highlight_640x360.jpg — 200 — 0 B — 3 ms — h2https://www.loc.gov/static/js/lib/mediaelement-4.2.8/mejs-controls.svgwww.loc.gov/static/js/lib/mediaelem... https://www.loc.gov/static/js/lib/mediaelement-4.2.8/mejs-controls.svg — 200 — 4.6 KiB — 19 ms — h2https://www.loc.gov/favicon.icowww.loc.gov/favicon.ico https://www.loc.gov/favicon.ico — 301 — 2.3 KiB — 18 ms — h2https://www.loc.gov/static/images/favicons/favicon.icowww.loc.gov/static/images/favicons/... https://www.loc.gov/static/images/favicons/favicon.ico — 200 — 33.9 KiB — 21 ms — h2https://smon.loc.gov/b/ss/locgovprod/1/JS-2.27.0-LGPQ/s71630867521996?AQB=1&ndh=1&pf=1&t=16%2F3%2F2026%2017%3A49%3A15%204%200&mid=19724936248218574191462401772914829762&aamlh=7&ce=UTF-8&cdp=2&fpCookieDomainPeriods=2&cl=SESSION&g=https%3A%2F%2Fwww.loc.gov%2F&c.&getPageLoadTime=2.0.2&performanceWriteFull=1.0&performanceWritePart=1.0&performanceCheck=1.0&p_fo=3.0&getPreviousValue=3.0.1&apl=4.0&inList=3.0&.c&cc=USD&server=www.loc.gov&events=event40&aamb=6G1ynYcLPuiQxYZrsz_pkqfLG9yMXBpb2zX5dvJdYQJzPXImdj0y&c1=Home%20%7C%20Library%20of%20Congress&v8=year%3D2026%20%7C%20month%3DApril%20%7C%20date%3D16%20%7C%20day%3DThursday%20%7C%20time%3D1%3A49%20PM&v15=https%3A%2F%2Fwww.loc.gov%2F&c61=home&c68=0.44&s=800x600&c=24&j=1.6&v=N&k=Y&bw=1350&bh=940&mcorgid=0D15148954E6C5100A4C98BC%40AdobeOrg&AQE=1smon.loc.gov/b/ss/locgovprod/1/JS-2... https://smon.loc.gov/b/ss/locgovprod/1/JS-2.27.0-LGPQ/s71630867521996?AQB=1&ndh=1&pf=1&t=16%2F3%2F2026%2017%3A49%3A15%204%200&mid=19724936248218574191462401772914829762&aamlh=7&ce=UTF-8&cdp=2&fpCookieDomainPeriods=2&cl=SESSION&g=https%3A%2F%2Fwww.loc.gov%2F&c.&getPageLoadTime=2.0.2&performanceWriteFull=1.0&performanceWritePart=1.0&performanceCheck=1.0&p_fo=3.0&getPreviousValue=3.0.1&apl=4.0&inList=3.0&.c&cc=USD&server=www.loc.gov&events=event40&aamb=6G1ynYcLPuiQxYZrsz_pkqfLG9yMXBpb2zX5dvJdYQJzPXImdj0y&c1=Home%20%7C%20Library%20of%20Congress&v8=year%3D2026%20%7C%20month%3DApril%20%7C%20date%3D16%20%7C%20day%3DThursday%20%7C%20time%3D1%3A49%20PM&v15=https%3A%2F%2Fwww.loc.gov%2F&c61=home&c68=0.44&s=800x600&c=24&j=1.6&v=N&k=Y&bw=1350&bh=940&mcorgid=0D15148954E6C5100A4C98BC%40AdobeOrg&AQE=1 — 200 — 298 B — 15 ms — h2
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 791ms · 3633KB · $5/mo
www.loc.gov
Other
Costly
Execution 201ms
Transfer 3120 KB
Unused 69%
Monthly Cost $1/mo
Unattributable
Other
Optional
Execution 190ms
Transfer 0 KB
Monthly Cost $1/mo
www.loc.gov
Other
Optional
Execution 178ms
Transfer 171 KB
Monthly Cost $1/mo
www.loc.gov
Other
Optional
Execution 141ms
Transfer 261 KB
Unused 39%
Monthly Cost $1/mo
assets.adobedtm.com
Other
Optional
Execution 81ms
Transfer 80 KB
Unused 37%
Monthly Cost $0/mo

These scripts may cost more than they're worth

  • www.loc.gov adds 201ms and costs ~$1/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.loc.gov 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

69% of www.loc.gov'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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