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Performance

· 15 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
82
GRADE
B
FIX
2
REVIEW
5
PASS
6
INFO
2

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

Mobile Desktop
86
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.

1.36 s

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

2.01 s

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

30 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.

1.36 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.

2.07 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, 29 requests
REVIEW
1.3 MB transferred, 29 requests
Info::
Page weighs 1.9 MB (1.3 MB transferred)
Warning::
JavaScript is 503 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 503 KB
Info::
29 HTTP requests
Info::
Estimated 0.27 g CO2 per page load
1.3 MB / 2.4 MB budget
1.3 MB transferred
29 requests
0.27 g CO2 per page load
Images 581.6 KiB 45%
JavaScript 502.7 KiB 38%
Fonts 129.4 KiB 10%
CSS 76.7 KiB 6%
HTML 12.1 KiB 1%
Other 2.4 KiB 0%
Other 1.1 KiB 0%
Other 730 B 0%
0 2.4 MB 4.9 MB
Under budget

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

B
Image Optimization
7 images, 0 KB saveable
REVIEW
7 images, 0 KB saveable
Warning::
https://web.mit.edu/files/images/202604/MIT-Brian-... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
7 images 582 KB
0 oversized -0 KB
7 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

C
JS Bundles
Action
6 scripts, 252 KB unused
REVIEW
6 scripts, 252 KB unused
Warning::
https://web.mit.edu/themes/mit/assets/js/main.js?t...: 184 KB unused (50%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.googletagmanager.com/gtm.js?id=GTM-M8M...: 67 KB unused (57%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 252 KB
252 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://web.mit.edu/themes/mit/assets/js/main.js?t5zcu8367 KB184 KB (50%)✓3rd
https://www.googletagmanager.com/gtm.js?id=GTM-M8MGV4P119 KB67 KB (57%)✓3rd
https://web.mit.edu/themes/mit/assets/js/modernizr.js?t5zcu86 KB—✓3rd
https://web.mit.edu/themes/mit/assets/js/SpotlightsExploreMoreLink.24ae33fb185156d3181a.js2 KB—✓3rd
https://web.mit.edu/themes/mit/assets/js/SpotlightsRecent.d6a3aa4b97b1659f1bbb.js5 KB—✓3rd
https://web.mit.edu/themes/mit/assets/js/Notification.11fc703b491d61aecf97.js4 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
29 resources · 1.3 MB · 252 KB savings available
REVIEW
29 resources · 1.3 MB · 252 KB savings available
Warning::
Page weight 283 KB over 1MB target
Got: 1.3 MB Expected: ≤ 1 MB
Info::
~252 KB of savings available
Warning::
28 third-party resources (100% of weight)
Info::
2 resources over 200KB
29 resources · 1.3 MiB · 28 third-party 282.7 KiB over 1MB target
Image 45% · 582.5 KiB
JavaScript 38% · 502.7 KiB
Font 10% · 129.4 KiB
CSS 6% · 76.7 KiB
Document 1% · 14.5 KiB
Other 0% · 897 B

~251.5 KiB of savings available

Remove unused JavaScript: 251.5 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
483ms total JS execution
PASS
483ms total JS execution
Info::
https://web.mit.edu/themes/mit/assets/js/main.js?t...: 140ms CPU time
Info::
https://web.mit.edu/: 122ms CPU time
Info::
https://www.googletagmanager.com/gtm.js?id=GTM-M8M...: 82ms CPU time
Info::
https://web.mit.edu/themes/mit/assets/js/modernizr...: 72ms CPU time
Info::
Unattributable: 67ms CPU time
Warning::
Third-party scripts: 483ms (100% of total)

Main Thread Breakdown

Script Evaluation 38% Other 29% Style & Layout 20% Script Parsing & Compilation 6% Parse HTML & CSS 4% Rendering 3%
ScriptTotalScriptingParse/CompileParty
https://web.mit.edu/themes/mit/assets/js/main.js?t5zcu8140ms105ms18ms3rd
https://web.mit.edu/122ms4ms1ms3rd
https://www.googletagmanager.com/gtm.js?id=GTM-M8MGV4P82ms64ms13ms3rd
https://web.mit.edu/themes/mit/assets/js/modernizr.js?t5zcu872ms5ms0ms3rd
Unattributable67ms2ms0ms3rd
A+
Font Loading
5 fonts (129 KB)
PASS
5 fonts (129 KB)
Info::
5 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

5

129 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 FCP 1.4 s LCP 2.0 shttps://use.typekit.net/af/912d1e/00000000000000007735bb33/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3l https://use.typekit.net/af/912d1e/00000000000000007735bb33/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 25.9 KiB — 28 ms — font-display: swaphttps://use.typekit.net/af/2288cb/00000000000000007735bb39/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3l https://use.typekit.net/af/2288cb/00000000000000007735bb39/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3 — 27.2 KiB — 37 ms — font-display: swaphttps://use.typekit.net/af/c002e2/00000000000000007735bb32/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3l https://use.typekit.net/af/c002e2/00000000000000007735bb32/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 28.0 KiB — 30 ms — font-display: swaphttps://use.typekit.net/af/216c2e/00000000000000007735bb6a/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3l https://use.typekit.net/af/216c2e/00000000000000007735bb6a/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3 — 25.4 KiB — 33 ms — font-display: swaphttps://use.typekit.net/af/174ae3/00000000000000007735bb5a/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3l https://use.typekit.net/af/174ae3/00000000000000007735bb5a/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 22.9 KiB — 40 ms — font-display: swap
l woff2 swap
Size 26 KB
Load time 28 ms
Start 501 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 27 KB
Load time 37 ms
Start 502 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 28 KB
Load time 30 ms
Start 502 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 25 KB
Load time 33 ms
Start 503 ms
Risk FOUT — text flashes from fallback to web font
l woff2 swap
Size 23 KB
Load time 40 ms
Start 503 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
29 requests over 1083ms
INFO
0 ms 500 ms 1.0 s 1.5 s 2.0 s FCP 1.4 s LCP 2.0 shttps://mit.edu// https://mit.edu/ — 302 — 167 B — 17 ms — http/1.1https://web.mit.edu/web.mit.edu/ https://web.mit.edu/ — 200 — 12.1 KiB — 177 ms — http/1.1https://web.mit.edu/themes/mit/assets/css/main.css?t5zcu8web.mit.edu/themes/mit/assets/css/m... https://web.mit.edu/themes/mit/assets/css/main.css?t5zcu8 — 200 — 75.1 KiB — 170 ms — http/1.1https://web.mit.edu/files/images/202604/MIT-Brian-Robinson-SL_0.jpgweb.mit.edu/files/images/202604/MIT... https://web.mit.edu/files/images/202604/MIT-Brian-Robinson-SL_0.jpg — 200 — 245.4 KiB — 184 ms — http/1.1https://web.mit.edu/themes/mit/assets/js/modernizr.js?t5zcu8web.mit.edu/themes/mit/assets/js/mo... https://web.mit.edu/themes/mit/assets/js/modernizr.js?t5zcu8 — 200 — 6.1 KiB — 158 ms — http/1.1https://web.mit.edu/themes/mit/assets/js/main.js?t5zcu8web.mit.edu/themes/mit/assets/js/ma... https://web.mit.edu/themes/mit/assets/js/main.js?t5zcu8 — 200 — 367.2 KiB — 205 ms — http/1.1https://use.typekit.net/uby1wjv.cssuse.typekit.net/uby1wjv.css https://use.typekit.net/uby1wjv.css — 200 — 1.4 KiB — 17 ms — h2https://web.mit.edu/themes/mit/assets/favicon/manifest.webmanifestweb.mit.edu/themes/mit/assets/favic... https://web.mit.edu/themes/mit/assets/favicon/manifest.webmanifest — 200 — 730 B — 176 ms — http/1.1https://p.typekit.net/p.css?s=1&k=uby1wjv&ht=tk&f=39496.39497.39498.39499.39500.39501.39502.39503.39504.39505.39506.39507.39508.39509&a=53548716&app=typekit&e=cssp.typekit.net/p.css?s=1&k=uby1wjv&h... https://p.typekit.net/p.css?s=1&k=uby1wjv&ht=tk&f=39496.39497.39498.39499.39500.39501.39502.39503.39504.39505.39506.39507.39508.39509&a=53548716&app=typekit&e=css — 200 — 172 B — 14 ms — h2https://www.googletagmanager.com/gtm.js?id=GTM-M8MGV4Pwww.googletagmanager.com/gtm.js?id=... https://www.googletagmanager.com/gtm.js?id=GTM-M8MGV4P — 200 — 118.9 KiB — 33 ms — h2https://use.typekit.net/af/912d1e/00000000000000007735bb33/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3use.typekit.net/af/912d1e/000000000... https://use.typekit.net/af/912d1e/00000000000000007735bb33/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n4&v=3 — 200 — 25.9 KiB — 28 ms — h2https://use.typekit.net/af/2288cb/00000000000000007735bb39/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3use.typekit.net/af/2288cb/000000000... https://use.typekit.net/af/2288cb/00000000000000007735bb39/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3 — 200 — 27.2 KiB — 37 ms — h2https://use.typekit.net/af/c002e2/00000000000000007735bb32/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3use.typekit.net/af/c002e2/000000000... https://use.typekit.net/af/c002e2/00000000000000007735bb32/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 200 — 28.0 KiB — 30 ms — h2https://use.typekit.net/af/216c2e/00000000000000007735bb6a/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3use.typekit.net/af/216c2e/000000000... https://use.typekit.net/af/216c2e/00000000000000007735bb6a/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n7&v=3 — 200 — 25.4 KiB — 33 ms — h2https://use.typekit.net/af/174ae3/00000000000000007735bb5a/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3use.typekit.net/af/174ae3/000000000... https://use.typekit.net/af/174ae3/00000000000000007735bb5a/31/l?primer=7cdcb44be4a7db8877ffa5c0007b8dd865b3bbc383831fe2ea177f62257a9191&fvd=n5&v=3 — 200 — 22.9 KiB — 40 ms — h2https://web.mit.edu/files/images/202604/Blue-Economy_02dw.jpgweb.mit.edu/files/images/202604/Blu... https://web.mit.edu/files/images/202604/Blue-Economy_02dw.jpg — 200 — 37.0 KiB — 186 ms — http/1.1https://web.mit.edu/files/images/202604/MIT-1S1-Energy-SLsub.jpgweb.mit.edu/files/images/202604/MIT... https://web.mit.edu/files/images/202604/MIT-1S1-Energy-SLsub.jpg — 200 — 62.2 KiB — 161 ms — http/1.1https://web.mit.edu/files/images/202604/artemis-ii-launch-nasa-00_dw.jpgweb.mit.edu/files/images/202604/art... https://web.mit.edu/files/images/202604/artemis-ii-launch-nasa-00_dw.jpg — 200 — 45.2 KiB — 183 ms — http/1.1https://web.mit.edu/files/images/202603/MIT-Hand-Tracker-SLsub.jpgweb.mit.edu/files/images/202603/MIT... https://web.mit.edu/files/images/202603/MIT-Hand-Tracker-SLsub.jpg — 200 — 48.6 KiB — 182 ms — http/1.1https://web.mit.edu/files/images/202505/Final-Thumbnails-Filehm.jpgweb.mit.edu/files/images/202505/Fin... https://web.mit.edu/files/images/202505/Final-Thumbnails-Filehm.jpg — 200 — 58.6 KiB — 216 ms — http/1.1https://web.mit.edu/files/images/202505/MIT-This-is-MIT-SLsub_0_0.jpgweb.mit.edu/files/images/202505/MIT... https://web.mit.edu/files/images/202505/MIT-This-is-MIT-SLsub_0_0.jpg — 200 — 84.6 KiB — 166 ms — http/1.1https://web.mit.edu/spotlights-export/suggested-links/?_format=jsonweb.mit.edu/spotlights-export/sugge... https://web.mit.edu/spotlights-export/suggested-links/?_format=json — 200 — 835 B — 154 ms — http/1.1https://web.mit.edu/themes/mit/assets/js/SpotlightsExploreMoreLink.24ae33fb185156d3181a.jsweb.mit.edu/themes/mit/assets/js/Sp... https://web.mit.edu/themes/mit/assets/js/SpotlightsExploreMoreLink.24ae33fb185156d3181a.js — 200 — 1.7 KiB — 181 ms — http/1.1https://web.mit.edu/themes/mit/assets/js/SpotlightsRecent.d6a3aa4b97b1659f1bbb.jsweb.mit.edu/themes/mit/assets/js/Sp... https://web.mit.edu/themes/mit/assets/js/SpotlightsRecent.d6a3aa4b97b1659f1bbb.js — 200 — 5.2 KiB — 170 ms — http/1.1https://web.mit.edu/themes/mit/assets/js/Notification.11fc703b491d61aecf97.jsweb.mit.edu/themes/mit/assets/js/No... https://web.mit.edu/themes/mit/assets/js/Notification.11fc703b491d61aecf97.js — 200 — 3.7 KiB — 153 ms — http/1.1https://web.mit.edu/spotlights-export/announcements/?_format=jsonweb.mit.edu/spotlights-export/annou... https://web.mit.edu/spotlights-export/announcements/?_format=json — 200 — 565 B — 178 ms — http/1.1https://web.mit.edu/spotlights-export/recent/?_format=jsonweb.mit.edu/spotlights-export/recen... https://web.mit.edu/spotlights-export/recent/?_format=json — 200 — 1.0 KiB — 172 ms — http/1.1https://web.mit.edu/spotlights-export/recent/?_format=jsonweb.mit.edu/spotlights-export/recen... https://web.mit.edu/spotlights-export/recent/?_format=json — 200 — 0 B — 166 ms — http/1.1https://web.mit.edu/themes/mit/assets/favicon/favicon.svgweb.mit.edu/themes/mit/assets/favic... https://web.mit.edu/themes/mit/assets/favicon/favicon.svg — 200 — 987 B — 155 ms — http/1.1
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 483ms · 504KB · $6/mo
web.mit.edu
Other
Optional
Execution 140ms
Transfer 367 KB
Unused 50%
Monthly Cost $2/mo
web.mit.edu
Other
Optional
Execution 122ms
Transfer 12 KB
Monthly Cost $2/mo
Google Tag Manager
Tag Manager
Optional
Execution 82ms
Transfer 119 KB
Unused 57%
Monthly Cost $1/mo
web.mit.edu
Other
Optional
Execution 72ms
Transfer 6 KB
Monthly Cost $1/mo
Unattributable
Other
Optional
Execution 67ms
Transfer 0 KB
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.

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

50% of web.mit.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

57% 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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