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Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
77
GRADE
C
FIX
2
REVIEW
3
PASS
7
INFO
2

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

Mobile Desktop
87
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
96
Accessibility Measures how accessible the page is for users with disabilities. Checks color contrast, ARIA labels, and semantic HTML.
81
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.

503 ms

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

2.39 s

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

6 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.

914 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.

2.72 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
14
7 PASS 3 REVIEW 2 FIX
F
Page Weight Budget
Action
3.7 MB transferred, 84 requests
FIX
3.7 MB transferred, 84 requests
Warning::
Page weighs 6.6 MB (3.7 MB transferred)
Warning::
Images are 2.5 MB — compress or use modern formats
Convert images to WebP/AVIF and resize to display dimensions to reduce transfer size.
Got: 2.5 MB
Warning::
JavaScript is 880 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 880 KB
Info::
84 HTTP requests
Info::
Estimated 0.78 g CO2 per page load
3.7 MB / 2.4 MB budget
3.7 MB transferred
84 requests
0.78 g CO2 per page load
Images 2.5 MiB 68%
JavaScript 879.5 KiB 23%
Fonts 186.8 KiB 5%
CSS 107.5 KiB 3%
HTML 31.7 KiB 1%
Other 8.6 KiB 0%
Other 1.1 KiB 0%
Other 559 B 0%
Other 550 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

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

D
JS Bundles
Action
21 scripts, 405 KB unused
FIX
21 scripts, 405 KB unused
Warning::
https://www.harvard.edu/wp-content/themes/core/ass...: 138 KB unused (86%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtag/js?id=G-KBLB...: 64 KB unused (42%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-5SG...: 64 KB unused (45%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.google.com/cse/static/element/b33cba58...: 49 KB unused (50%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://connect.facebook.net/en_US/fbevents.js: 37 KB unused (39%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 405 KB
405 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.harvard.edu/wp-content/themes/core/assets/js/dist/theme/vendor.min.js?ver=5b4e48cf0fbd9ab8d8f2c32ec81b6cf96e8c138e7bde68035416aad021a85c7d15959b77e4103dbacc48c75561d99a307a31ef22b69513c11e9d57a52dd9594c161 KB138 KB (86%)✓1st
https://www.googletagmanager.com/gtag/js?id=G-KBLBYHG5EP&cx=c&gtm=4e6460h1153 KB64 KB (42%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-5SGSF6G142 KB64 KB (45%)✓3rd
https://www.google.com/cse/static/element/b33cba5881f68fbf/cse_element__en.js?usqp=CAI%3D99 KB49 KB (50%)✓3rd
https://connect.facebook.net/en_US/fbevents.js95 KB37 KB (39%)✓3rd
https://cse.google.com/adsense/search/async-ads.js44 KB31 KB (73%)✓3rd
https://www.harvard.edu/wp-content/themes/core/assets/js/vendor/jquery.min.js?ver=3.4.131 KB23 KB (74%)✓1st
https://www.harvard.edu/wp-includes/js/dist/i18n.min.js?ver=c26c3dc7bed3667933752 KB—✓1st
https://www.harvard.edu/wp-includes/js/dist/hooks.min.js?ver=dd5603f07f9220ed27f12 KB—✓1st
https://cse.google.com/cse.js?cx=006776768860476326824:n4rl30fjc-e4 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

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
Image Optimization
Action
46 images, 0 KB saveable
REVIEW
46 images, 0 KB saveable
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2023/11... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2023/11... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/themes/core/ass... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2023/11... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2023/11... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/themes/core/ass... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2023/11... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.harvard.edu/wp-content/uploads/2026/03... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
46 images 2.5 MB
0 oversized -0 KB
13 legacy format
24 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

Performance issues directly impact user engagement and conversion rates.

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
789ms total JS execution
REVIEW
789ms total JS execution
Warning::
https://www.harvard.edu/: 369ms CPU time
Info::
Unattributable: 146ms CPU time
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-5SG...: 91ms CPU time
Info::
https://www.googletagmanager.com/gtag/js?id=G-KBLB...: 67ms CPU time
Info::
https://www.harvard.edu/wp-content/themes/core/ass...: 61ms CPU time
Info::
Third-party scripts: 304ms (38% of total)

Main Thread Breakdown

Script Evaluation 37% Other 25% Style & Layout 22% Script Parsing & Compilation 10% Parse HTML & CSS 4%
ScriptTotalScriptingParse/CompileParty
https://www.harvard.edu/369ms4ms2ms1st
Unattributable146ms22ms0ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-5SGSF6G91ms68ms19ms3rd
https://www.googletagmanager.com/gtag/js?id=G-KBLBYHG5EP&cx=c&gtm=4e6460h167ms49ms16ms3rd
https://www.harvard.edu/wp-content/themes/core/assets/js/dist/theme/scripts.min.js?ver=e96cd733acfdfb3909cc0cb04a087f664206a8de87a4155863efaff221e67dd0693af3ebb48029ad20da849db0c2541451694c11732de2a206c55360f5ed521861ms53ms5ms1st
https://www.harvard.edu/wp-content/themes/core/assets/js/dist/theme/vendor.min.js?ver=5b4e48cf0fbd9ab8d8f2c32ec81b6cf96e8c138e7bde68035416aad021a85c7d15959b77e4103dbacc48c75561d99a307a31ef22b69513c11e9d57a52dd9594c55ms16ms17ms1st
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Third-Party Impact
20% third-party, 0 ms blocking
PASS
20% third-party, 0 ms blocking
Info::
Third-party code accounts for 20% of page weight (751.3 KiB of 3.7 MiB)
Info::
Third-party blocking time is low (0 ms)
80%
20%
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
5 fonts (187 KB)
PASS
5 fonts (187 KB)
Info::
5 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

5

187 KB total

Render-blocking

0

of 5

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 2.0 s 2.5 s FCP 503 ms LCP 2.4 shttps://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/gt-america/GT-America-Standard-Regular.woff2GT-America-Standard-Reg... https://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/gt-america/GT-America-Standard-Regular.woff2 — 47.9 KiB — 0 ms — font-display: swaphttps://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/icons-core/core-icons.ttf?4g884ccore-icons.ttf https://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/icons-core/core-icons.ttf?4g884c — 2.7 KiB — 0 ms — font-display: swaphttps://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/gt-america/GT-America-Standard-Medium.woff2GT-America-Standard-Med... https://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/gt-america/GT-America-Standard-Medium.woff2 — 51.2 KiB — 0 ms — font-display: swaphttps://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/canela/CanelaDeck-Regular-Web.woff2CanelaDeck-Regular-Web.... https://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/canela/CanelaDeck-Regular-Web.woff2 — 33.6 KiB — 0 ms — font-display: swaphttps://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/gt-america/GT-America-Standard-Bold.woff2GT-America-Standard-Bol... https://www.harvard.edu/wp-content/themes/core/assets/fonts/theme/gt-america/GT-America-Standard-Bold.woff2 — 51.3 KiB — 0 ms — font-display: swap
GT-America-Standard-Reg... woff2 swap
Size 48 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
core-icons.ttf ttf swap
Size 3 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
GT-America-Standard-Med... woff2 swap
Size 51 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
CanelaDeck-Regular-Web.... woff2 swap
Size 34 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
GT-America-Standard-Bol... woff2 swap
Size 51 KB
Load time 0 ms
Start 0 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 ~1 KB and ~2 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
HTTP Caching
max-age=300 (5 minutes)
PASS
max-age=300 (5 minutes)
Info::
Cache-Control header is set
Got: max-age=300, must-revalidate
Info::
Effective TTL: 5 minutes (max-age=300)
Info::
No ETag or Last-Modified header
Conditional requests (304 Not Modified) are not possible without validators.
Cache-Control

max-age=300, must-revalidate

DirectiveValueMeaning
max-age300Cache for 5 minutes
must-revalidate—Must recheck with server after expiry
Effective TTL: 300 seconds
Network Waterfall
84 requests over 0ms
INFO

Performance analysis not available for this result.

Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
38% of JavaScript execution is third-party
First-party Third-party 304ms · 295KB · $4/mo
Unattributable
Other
Optional
Execution 146ms
Transfer 0 KB
Monthly Cost $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 91ms
Transfer 142 KB
Unused 45%
Monthly Cost $1/mo
Google Tag Manager
Tag Manager
Optional
Execution 67ms
Transfer 153 KB
Unused 42%
Monthly Cost $1/mo

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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