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Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
85
GRADE
B
FIX
2
REVIEW
5
PASS
6
INFO
2

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

Mobile Desktop
91
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
100
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.

1.21 s

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

1.52 s

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

0 ms

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

0.019

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

1.51 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.

1.52 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
6 PASS 5 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 (1.3 MiB of 1.3 MiB)
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.

B
Page Weight Budget
1.3 MB transferred, 39 requests
REVIEW
1.3 MB transferred, 39 requests
Info::
Page weighs 2.3 MB (1.3 MB transferred)
Info::
39 HTTP requests
Info::
Estimated 0.28 g CO2 per page load
1.3 MB / 2.4 MB budget
1.3 MB transferred
39 requests
0.28 g CO2 per page load
Images 894.1 KiB 65%
JavaScript 252.0 KiB 18%
Fonts 128.8 KiB 9%
CSS 68.6 KiB 5%
HTML 19.4 KiB 1%
Other 1.6 KiB 0%
Other 551 B 0%
Other 519 B 0%
0 2.4 MB 4.9 MB
Under budget
B
Image Optimization
19 images, 0 KB saveable
REVIEW
19 images, 0 KB saveable
Warning::
https://www.princeton.edu/themes/custom/hobbes/ima... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
19 images 894 KB
0 oversized -0 KB
8 legacy format
1 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

B
JS Bundles
4 scripts, 101 KB unused
REVIEW
4 scripts, 101 KB unused
Warning::
https://www.googletagmanager.com/gtag/js?id=G-92L6...: 65 KB unused (41%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.princeton.edu/sites/default/files/js/j...: 36 KB unused (59%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 101 KB
101 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtag/js?id=G-92L6B9PQCG160 KB65 KB (41%)✓3rd
https://www.princeton.edu/sites/default/files/js/js_n_4nz7oMlCkH0q4hR8K78HjM_rgGDfSM4XjP0wa8xM4.js?scope=footer&delta=0&language=en&theme=hobbes&include=eJxVzVEOgyAQRdENQVlS89BxHIsOYcCWrr7GxCb-3OR8XVblRM8KDnzE8d0PLPi4WWMkCzHh2y8MFR5FcHkm7H2xP3WlDCY_EWorNPoJQ0u1e0syUnFJtlduJatRkE2q24XeFs6e1x_B4jsV61 KB36 KB (59%)✓3rd
https://www.princeton.edu/sites/default/files/js/js_VHwiQXABniyTQ5hjlZvVRtZrYuDQdpJ1pdKmiT6mdFo.js?scope=header&delta=0&language=en&theme=hobbes&include=eJxVzVEOgyAQRdENQVlS89BxHIsOYcCWrr7GxCb-3OR8XVblRM8KDnzE8d0PLPi4WWMkCzHh2y8MFR5FcHkm7H2xP3WlDCY_EWorNPoJQ0u1e0syUnFJtlduJatRkE2q24XeFs6e1x_B4jsV30 KB—✓3rd
https://www.princeton.edu/modules/contrib/google_tag/js/gtag.js?tcretc1 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

C
Page Weight Inventory
Action
39 resources · 1.3 MB · 101 KB savings available
REVIEW
39 resources · 1.3 MB · 101 KB savings available
Warning::
Page weight 342 KB over 1MB target
Got: 1.3 MB Expected: ≤ 1 MB
Info::
~101 KB of savings available
Warning::
38 third-party resources (100% of weight)
Info::
1 resources over 200KB
39 resources · 1.3 MiB · 38 third-party 341.6 KiB over 1MB target
Image 66% · 895.6 KiB
JavaScript 18% · 252.0 KiB
Font 9% · 128.8 KiB
CSS 5% · 68.6 KiB
Document 1% · 19.4 KiB
Other 0% · 1.2 KiB

~100.7 KiB of savings available

Remove unused JavaScript: 100.7 KiB
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

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+
JS Execution Cost
360ms total JS execution
PASS
360ms total JS execution
Info::
https://www.princeton.edu/: 182ms CPU time
Info::
https://www.princeton.edu/sites/default/files/js/j...: 62ms CPU time
Info::
Unattributable: 62ms CPU time
Info::
https://www.googletagmanager.com/gtag/js?id=G-92L6...: 53ms CPU time
Warning::
Third-party scripts: 360ms (100% of total)

Main Thread Breakdown

Other 41% Script Evaluation 26% Style & Layout 22% Parse HTML & CSS 4% Script Parsing & Compilation 4% Rendering 3%
ScriptTotalScriptingParse/CompileParty
https://www.princeton.edu/182ms2ms0ms3rd
https://www.princeton.edu/sites/default/files/js/js_n_4nz7oMlCkH0q4hR8K78HjM_rgGDfSM4XjP0wa8xM4.js?scope=footer&delta=0&language=en&theme=hobbes&include=eJxVzVEOgyAQRdENQVlS89BxHIsOYcCWrr7GxCb-3OR8XVblRM8KDnzE8d0PLPi4WWMkCzHh2y8MFR5FcHkm7H2xP3WlDCY_EWorNPoJQ0u1e0syUnFJtlduJatRkE2q24XeFs6e1x_B4jsV62ms41ms4ms3rd
Unattributable62ms1ms0ms3rd
https://www.googletagmanager.com/gtag/js?id=G-92L6B9PQCG53ms44ms9ms3rd
A+
Font Loading
6 fonts (129 KB)
PASS
6 fonts (129 KB)
Info::
6 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

6

129 KB total

Render-blocking

0

of 6

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 500 ms 1.0 s 1.5 s FCP 1.2 s LCP 1.5 shttps://use.typekit.net/af/2e6f07/000000000000000000011ce6/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3l https://use.typekit.net/af/2e6f07/000000000000000000011ce6/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 15.5 KiB — 8 ms — font-display: swaphttps://use.typekit.net/af/8d9b32/0000000000000000000118bf/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3l https://use.typekit.net/af/8d9b32/0000000000000000000118bf/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 11.7 KiB — 13 ms — font-display: swaphttps://use.typekit.net/af/b825af/0000000000000000000118b1/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3l https://use.typekit.net/af/b825af/0000000000000000000118b1/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3 — 15.4 KiB — 12 ms — font-display: swaphttps://use.typekit.net/af/9cb78a/0000000000000000000118ad/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3l https://use.typekit.net/af/9cb78a/0000000000000000000118ad/27/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 16.0 KiB — 9 ms — font-display: swaphttps://use.typekit.net/af/82db8a/000000000000000077359dfa/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3l https://use.typekit.net/af/82db8a/000000000000000077359dfa/30/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 35.9 KiB — 10 ms — font-display: swaphttps://www.princeton.edu/themes/custom/hobbes/fonts/princetonmonticello_regular/hinted-PrincetonMonti-Regular.woff2hinted-PrincetonMonti-R... https://www.princeton.edu/themes/custom/hobbes/fonts/princetonmonticello_regular/hinted-PrincetonMonti-Regular.woff2 — 34.3 KiB — 36 ms — font-display: swap
l woff2 swap
Size 15 KB
Load time 8 ms
Start 994 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 12 KB
Load time 13 ms
Start 995 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 15 KB
Load time 12 ms
Start 995 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 16 KB
Load time 9 ms
Start 995 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 36 KB
Load time 10 ms
Start 995 ms
Risk FOUT — text flashes from fallback to web font
hinted-PrincetonMonti-R... woff2 swap
Size 34 KB
Load time 36 ms
Start 995 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
No optimization needed
PASS
No optimization needed
Info::
No resource hint issues
Network Waterfall
39 requests over 1328ms
INFO
0 ms 500 ms 1.0 s 1.5 s FCP 1.2 s LCP 1.5 shttps://princeton.edu// https://princeton.edu/ — 302 — 130 B — 491 ms — http/1.0https://www.princeton.edu/www.princeton.edu/ https://www.princeton.edu/ — 200 — 19.4 KiB — 315 ms — h2https://www.princeton.edu/sites/default/files/css/css_7P8V6wldKNzQtYx4zsHvFLPpgevRi6Af_nNUfVuRrgQ.css?delta=0&language=en&theme=hobbes&include=eJxFjEEOwkAIAD-Ey5ugS7pYWgi4an-vMWm8TDJzmMVTsOcMskZ3esNwZilczZnssjJdttuXXRJMjy1mhpegKSflCUFJa1KMumb_0uYRk01rSIc66yE7MpXAU-VV-GPbvU-TD1MSN0wwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/css/css_7P8V6wldKNzQtYx4zsHvFLPpgevRi6Af_nNUfVuRrgQ.css?delta=0&language=en&theme=hobbes&include=eJxFjEEOwkAIAD-Ey5ugS7pYWgi4an-vMWm8TDJzmMVTsOcMskZ3esNwZilczZnssjJdttuXXRJMjy1mhpegKSflCUFJa1KMumb_0uYRk01rSIc66yE7MpXAU-VV-GPbvU-TD1MSN0w — 200 — 1.9 KiB — 31 ms — h2https://use.typekit.net/stk8lop.cssuse.typekit.net/stk8lop.css https://use.typekit.net/stk8lop.css — 200 — 1.3 KiB — 42 ms — h2https://www.princeton.edu/sites/default/files/css/css_z7jtN4CMh_f2LrvxeTjxmj7MPv_NNuERaZV0FNCCjQI.css?delta=2&language=en&theme=hobbes&include=eJxFjEEOwkAIAD-Ey5ugS7pYWgi4an-vMWm8TDJzmMVTsOcMskZ3esNwZilczZnssjJdttuXXRJMjy1mhpegKSflCUFJa1KMumb_0uYRk01rSIc66yE7MpXAU-VV-GPbvU-TD1MSN0wwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/css/css_z7jtN4CMh_f2LrvxeTjxmj7MPv_NNuERaZV0FNCCjQI.css?delta=2&language=en&theme=hobbes&include=eJxFjEEOwkAIAD-Ey5ugS7pYWgi4an-vMWm8TDJzmMVTsOcMskZ3esNwZilczZnssjJdttuXXRJMjy1mhpegKSflCUFJa1KMumb_0uYRk01rSIc66yE7MpXAU-VV-GPbvU-TD1MSN0w — 200 — 65.2 KiB — 36 ms — h2https://www.princeton.edu/sites/default/files/js/js_VHwiQXABniyTQ5hjlZvVRtZrYuDQdpJ1pdKmiT6mdFo.js?scope=header&delta=0&language=en&theme=hobbes&include=eJxVzVEOgyAQRdENQVlS89BxHIsOYcCWrr7GxCb-3OR8XVblRM8KDnzE8d0PLPi4WWMkCzHh2y8MFR5FcHkm7H2xP3WlDCY_EWorNPoJQ0u1e0syUnFJtlduJatRkE2q24XeFs6e1x_B4jsVwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/js/js_VHwiQXABniyTQ5hjlZvVRtZrYuDQdpJ1pdKmiT6mdFo.js?scope=header&delta=0&language=en&theme=hobbes&include=eJxVzVEOgyAQRdENQVlS89BxHIsOYcCWrr7GxCb-3OR8XVblRM8KDnzE8d0PLPi4WWMkCzHh2y8MFR5FcHkm7H2xP3WlDCY_EWorNPoJQ0u1e0syUnFJtlduJatRkE2q24XeFs6e1x_B4jsV — 200 — 30.0 KiB — 50 ms — h2https://www.princeton.edu/modules/contrib/google_tag/js/gtag.js?tcretcwww.princeton.edu/modules/contrib/g... https://www.princeton.edu/modules/contrib/google_tag/js/gtag.js?tcretc — 200 — 790 B — 50 ms — h2https://www.princeton.edu/sites/default/files/styles/half_16_9_1440/public/images/2026/04/20260129_SpecialCollectionsUSA250th_MR_039.jpg?itok=089diqEEwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/styles/half_16_9_1440/public/images/2026/04/20260129_SpecialCollectionsUSA250th_MR_039.jpg?itok=089diqEE — 200 — 98.1 KiB — 62 ms — h2https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/04/Advancement_Quantum_Option_1_Web.jpeg?itok=z-K4PNkiwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/04/Advancement_Quantum_Option_1_Web.jpeg?itok=z-K4PNki — 200 — 44.9 KiB — 62 ms — h2https://p.typekit.net/p.css?s=1&k=stk8lop&ht=tk&f=12784.12785.12786.12788.12789.12790.10419.10421.12093.12094.12096.12097&a=27724391&app=typekit&e=cssp.typekit.net/p.css?s=1&k=stk8lop&h... https://p.typekit.net/p.css?s=1&k=stk8lop&ht=tk&f=12784.12785.12786.12788.12789.12790.10419.10421.12093.12094.12096.12097&a=27724391&app=typekit&e=css — 200 — 172 B — 41 ms — h2https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/04/20260407_Zervas-Futamura_040726_0008_4000x2250.jpg?itok=evgTWImtwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/04/20260407_Zervas-Futamura_040726_0008_4000x2250.jpg?itok=evgTWImt — 200 — 25.2 KiB — 30 ms — h2https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/03/20260319_christinakim_MR_083.jpg?itok=0_oOJ03rwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/03/20260319_christinakim_MR_083.jpg?itok=0_oOJ03r — 200 — 25.7 KiB — 30 ms — h2https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/04/20260325_3MinuteThesis_032526_0081_ET_1.jpg?itok=Xaq8Pmsvwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/04/20260325_3MinuteThesis_032526_0081_ET_1.jpg?itok=Xaq8Pmsv — 200 — 24.9 KiB — 35 ms — h2https://www.princeton.edu/sites/default/files/js/js_n_4nz7oMlCkH0q4hR8K78HjM_rgGDfSM4XjP0wa8xM4.js?scope=footer&delta=0&language=en&theme=hobbes&include=eJxVzVEOgyAQRdENQVlS89BxHIsOYcCWrr7GxCb-3OR8XVblRM8KDnzE8d0PLPi4WWMkCzHh2y8MFR5FcHkm7H2xP3WlDCY_EWorNPoJQ0u1e0syUnFJtlduJatRkE2q24XeFs6e1x_B4jsVwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/js/js_n_4nz7oMlCkH0q4hR8K78HjM_rgGDfSM4XjP0wa8xM4.js?scope=footer&delta=0&language=en&theme=hobbes&include=eJxVzVEOgyAQRdENQVlS89BxHIsOYcCWrr7GxCb-3OR8XVblRM8KDnzE8d0PLPi4WWMkCzHh2y8MFR5FcHkm7H2xP3WlDCY_EWorNPoJQ0u1e0syUnFJtlduJatRkE2q24XeFs6e1x_B4jsV — 200 — 61.2 KiB — 33 ms — h2https://www.princeton.edu/themes/custom/hobbes/icons/manifest.jsonwww.princeton.edu/themes/custom/hob... https://www.princeton.edu/themes/custom/hobbes/icons/manifest.json — 200 — 519 B — 62 ms — h2https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/03/20260325_Staff_Awards_Lunch_DJA_135_ET_0.jpg?itok=QV1hIgoqwww.princeton.edu/sites/default/fil... https://www.princeton.edu/sites/default/files/styles/third_1x_crop/public/images/2026/03/20260325_Staff_Awards_Lunch_DJA_135_ET_0.jpg?itok=QV1hIgoq — 200 — 40.8 KiB — 31 ms — h2https://www.princeton.edu/themes/custom/hobbes/images/logo-white.svgwww.princeton.edu/themes/custom/hob... https://www.princeton.edu/themes/custom/hobbes/images/logo-white.svg — 200 — 7.7 KiB — 32 ms — h2https://www.googletagmanager.com/gtag/js?id=G-92L6B9PQCGwww.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-92L6B9PQCG — 200 — 160.1 KiB — 254 ms — h2data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 96 96'%3E%3Ctitle%3ESearc…www.w3.org/2000/svg' viewBox='0 0 9... data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 96 96'%3E%3Ctitle%3ESearc… — 200 — 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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 360ms · 241KB · $5/mo
www.princeton.edu
Other
Optional
Execution 182ms
Transfer 19 KB
Monthly Cost $2/mo
www.princeton.edu
Other
Optional
Execution 62ms
Transfer 61 KB
Unused 59%
Monthly Cost $1/mo
Unattributable
Other
Optional
Execution 62ms
Transfer 0 KB
Monthly Cost $1/mo
Google Tag Manager
Tag Manager
Optional
Execution 53ms
Transfer 160 KB
Unused 41%
Monthly Cost $1/mo

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.

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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

59% of www.princeton.edu'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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