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https://bridgeslab.sph.umich.edu

Performance

· 23 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
87
GRADE
B
FIX
2
REVIEW
7
PASS
10
INFO
4

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

Mobile Desktop
82
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
83
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.

1.32 s

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

1.90 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.

0.000

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

2.61 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.

1.90 s

Page Load Progression

429 ms
858 ms
1.3 s
1.7 s
2.1 s
2.6 s
3.0 s
3.4 s
Checks
23
10 PASS 7 REVIEW 2 FIX
D
Third-Party Impact
Action
61% third-party, 0 ms blocking
FIX
61% third-party, 0 ms blocking
Warning::
Third-party code accounts for 61% of page weight (485.3 KiB of 795.2 KiB)
Info::
Third-party blocking time is low (0 ms)
39%
61%
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.

C
Image Optimization
Action
6 images, 0 KB saveable
REVIEW
6 images, 0 KB saveable
Warning::
https://bridgeslab.sph.umich.edu/lab_website-stati... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://bridgeslab.sph.umich.edu/lab_website-stati... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://bridgeslab.sph.umich.edu/lab_website-stati... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://scontent-det1-1.xx.fbcdn.net/v/t39.30808-1... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://bridgeslab.sph.umich.edu/lab_website-stati... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://bridgeslab.sph.umich.edu/lab_website-stati... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
6 images 64 KB
0 oversized -0 KB
6 legacy format
6 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

B
JS Bundles
4 scripts, 118 KB unused
REVIEW
4 scripts, 118 KB unused
Warning::
https://www.googletagmanager.com/gtag/js?id=G-HLFF...: 63 KB unused (43%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://connect.facebook.net/en_US/bundle/sdk.js/: 54 KB unused (69%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 118 KB
118 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.googletagmanager.com/gtag/js?id=G-HLFFK9ZMJE146 KB63 KB (43%)✓3rd
https://connect.facebook.net/en_US/bundle/sdk.js/78 KB54 KB (69%)✓3rd
https://cdn.jsdelivr.net/npm/bootstrap@5.3.7/dist/js/bootstrap.bundle.min.js24 KB—✓3rd
https://connect.facebook.net/en_US/sdk.js5 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

B
HTTP/3 (QUIC)
HTTP/3 not advertised
REVIEW
HTTP/3 not advertised
Info::
HTTP/3 (QUIC) is not advertised
HTTP/3 isn't advertised via Alt-Svc and the worker didn't negotiate h3. HTTP/3 reduces handshake latency (1-RTT instead of 2-3 RTTs) and is more resilient on lossy connections. Most modern CDNs (Cloudflare, Fastly, AWS CloudFront, Google Cloud CDN) support HTTP/3 with a single config switch -- consider enabling for mobile-heavy workloads.
C
Compression Algorithm
Action
Main response served uncompressed
REVIEW
Main response served uncompressed
Info::
Main HTML response has no Content-Encoding (uncompressed)
The main HTML document is served without compression. The Text Compression section above lists the broader picture; for the main response specifically, even gzip would shave ~70-80% off most text payloads.
B
Main HTML Cache-Control
No Cache-Control header on main HTML response
REVIEW
No Cache-Control header on main HTML response
Info::
Main HTML response has no Cache-Control header
Without an explicit Cache-Control, browsers fall back to heuristic caching (~10% of Last-Modified age). Set `Cache-Control: no-cache` or `max-age=300` for HTML to control freshness explicitly -- prevents stale auth state and SPA shell drift.
B
Server-Timing Observability
No Server-Timing header found
REVIEW
No Server-Timing header found
Info::
No Server-Timing header found
Server-Timing exposes backend timing breakdowns to browser DevTools (e.g., `db: 45ms; render: 120ms; cache: 2ms`). Useful for diagnosing slow pages without backend log access. Most modern frameworks (Next.js, Cloudflare Workers, Fastly) emit it automatically; absence on a managed platform usually means telemetry headers are stripped at the edge.
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A
Page Weight Budget
795 KB transferred, 17 requests
PASS
795 KB transferred, 17 requests
Info::
Page weighs 1.5 MB (795 KB transferred)
Info::
CSS is 315 KB — consider purging unused styles
Remove unused CSS rules with tools like PurgeCSS to reduce stylesheet size.
Got: 315 KB
Info::
17 HTTP requests
Info::
Estimated 0.16 g CO2 per page load
795 KB / 2.4 MB budget
795 KB transferred
17 requests
0.16 g CO2 per page load
CSS 315.0 KiB 40%
JavaScript 253.8 KiB 32%
Fonts 128.2 KiB 16%
Images 63.7 KiB 8%
HTML 31.8 KiB 4%
Other 2.1 KiB 0%
Other 555 B 0%
0 2.4 MB 4.9 MB
Under budget

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

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
160ms total JS execution
PASS
160ms total JS execution
Info::
https://bridgeslab.sph.umich.edu/: 80ms CPU time
Info::
https://www.googletagmanager.com/gtag/js?id=G-HLFF...: 79ms CPU time
Info::
Third-party scripts: 79ms (50% of total)

Main Thread Breakdown

Script Evaluation 35% Other 23% Style & Layout 22% Script Parsing & Compilation 13% Parse HTML & CSS 5%
ScriptTotalScriptingParse/CompileParty
https://bridgeslab.sph.umich.edu/80ms2ms1ms1st
https://www.googletagmanager.com/gtag/js?id=G-HLFFK9ZMJE79ms64ms15ms3rd
A+
Font Loading
1 fonts (128 KB)
PASS
1 fonts (128 KB)
Info::
1 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

1

128 KB total

Render-blocking

0

of 1

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 FCP 1.3 s LCP 1.9 shttps://cdn.jsdelivr.net/npm/bootstrap-icons@1.11.0/font/fonts/bootstrap-icons.woff2?1bb88866b4085542c8ed5fb61b9393ddbootstrap-icons.woff2 https://cdn.jsdelivr.net/npm/bootstrap-icons@1.11.0/font/fonts/bootstrap-icons.woff2?1bb88866b4085542c8ed5fb61b9393dd — 128.2 KiB — 21 ms — font-display: swap
bootstrap-icons.woff2 woff2 swap
Size 128 KB
Load time 21 ms
Start 3.3 s
Risk FOUT — text flashes from fallback to web font
  • Subset this font — over 100 KB suggests Latin Extended or full glyph coverage that most pages don't need
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 ~64 KB and ~128 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+
LCP Image Preload
LCP preload audit not available
PASS
LCP preload audit not available
Info::
LCP image preload audit not available for this scan
A+
Server Response Intelligence
2 server-response signal(s) detected
PASS
2 server-response signal(s) detected
Info::
`Vary` header declared: origin
The page declares a `Vary` header, telling downstream caches which request headers the response varies on. Critical for content-negotiated responses (compression, language, cookies, device class).
Info::
No `ETag` or `Last-Modified` -- conditional GET not supported
Without either header, browsers can't issue conditional GETs and refresh always re-downloads the full response body even when nothing changed. Add `ETag: "<hash>"` (or `Last-Modified: <date>`) on cacheable responses; the server returns 304 Not Modified when the client's cached copy is still valid, saving bandwidth.
A
Page Weight Inventory
17 resources · 795 KB · 118 KB savings available
PASS
17 resources · 795 KB · 118 KB savings available
Info::
Within 1MB page-weight target
Got: 795 KB
Info::
~118 KB of savings available
Warning::
10 third-party resources (61% of weight)
Info::
1 resources over 200KB
17 resources · 795.2 KiB · 10 third-party Within 1MB page-weight target
CSS 40% · 315.0 KiB
JavaScript 32% · 253.8 KiB
Font 16% · 128.2 KiB
Image 8% · 65.8 KiB
Document 4% · 31.8 KiB
Other 0% · 555 B

~117.5 KiB of savings available

Remove unused JavaScript: 117.5 KiB
Network Waterfall
17 requests over 3876ms
INFO
0 ms 1.0 s 2.0 s 3.0 s 4.0 s FCP 1.3 s LCP 1.9 shttps://bridgeslab.sph.umich.edu// https://bridgeslab.sph.umich.edu/ — 200 — 31.8 KiB — 2.6 s — http/1.1https://cdn.jsdelivr.net/npm/bootstrap@5.3.7/dist/css/bootstrap.min.csscdn.jsdelivr.net/npm/bootstrap@5.3.... https://cdn.jsdelivr.net/npm/bootstrap@5.3.7/dist/css/bootstrap.min.css — 200 — 33.2 KiB — 28 ms — h2https://cdn.jsdelivr.net/npm/bootstrap@5.3.7/dist/js/bootstrap.bundle.min.jscdn.jsdelivr.net/npm/bootstrap@5.3.... https://cdn.jsdelivr.net/npm/bootstrap@5.3.7/dist/js/bootstrap.bundle.min.js — 200 — 24.4 KiB — 27 ms — h2https://cdn.jsdelivr.net/npm/bootstrap-icons@1.11.0/font/bootstrap-icons.csscdn.jsdelivr.net/npm/bootstrap-icon... https://cdn.jsdelivr.net/npm/bootstrap-icons@1.11.0/font/bootstrap-icons.css — 200 — 14.1 KiB — 23 ms — h2https://bridgeslab.sph.umich.edu/lab_website-static/css/custom.css/lab_website-static/css/custom.css https://bridgeslab.sph.umich.edu/lab_website-static/css/custom.css — 200 — 267.8 KiB — 759 ms — http/1.1https://scontent-det1-1.xx.fbcdn.net/v/t39.30808-1/302994671_461759342664757_7704979863435545673_n.jpg?_nc_cat=108&ccb=1-7&_nc_sid=08baa4&_nc_ohc=F1FBTG-HaOIQ7kNvwGpFojo&_nc_oc=AdrWJDVQKwpAVMdTO3UQqh1MQ3zKZOXO7Z06aGZfKltq_meV9LljU5egzRGRW053LkU&_nc_zt=24&_nc_ht=scontent-det1-1.xx&edm=AJdBtusEAAAA&_nc_gid=elf7KFhFK4v4Es4DdBWfyA&_nc_tpa=Q5bMBQE-aXdHBWpYga_jXyDumAD5-8VgVj2lf-SWHuUyWuULXG9RuH4SgtnqTTmXztAc2npchM-WhlrU&oh=00_Af5VA2WFwtTFBqj-tJU9DF_VnIb8Soks-Itfia9_8GjCmQ&oe=6A065926scontent-det1-1.xx.fbcdn.net/v/t39.... https://scontent-det1-1.xx.fbcdn.net/v/t39.30808-1/302994671_461759342664757_7704979863435545673_n.jpg?_nc_cat=108&ccb=1-7&_nc_sid=08baa4&_nc_ohc=F1FBTG-HaOIQ7kNvwGpFojo&_nc_oc=AdrWJDVQKwpAVMdTO3UQqh1MQ3zKZOXO7Z06aGZfKltq_meV9LljU5egzRGRW053LkU&_nc_zt=24&_nc_ht=scontent-det1-1.xx&edm=AJdBtusEAAAA&_nc_gid=elf7KFhFK4v4Es4DdBWfyA&_nc_tpa=Q5bMBQE-aXdHBWpYga_jXyDumAD5-8VgVj2lf-SWHuUyWuULXG9RuH4SgtnqTTmXztAc2npchM-WhlrU&oh=00_Af5VA2WFwtTFBqj-tJU9DF_VnIb8Soks-Itfia9_8GjCmQ&oe=6A065926 — 200 — 53.4 KiB — 459 ms — h3https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/user.png/lab_website-static/img/icons/user.... https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/user.png — 200 — 2.2 KiB — 288 ms — http/1.1https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/paste.png/lab_website-static/img/icons/paste... https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/paste.png — 200 — 1.9 KiB — 392 ms — http/1.1https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/file.png/lab_website-static/img/icons/file.... https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/file.png — 200 — 1.7 KiB — 408 ms — http/1.1https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/world.png/lab_website-static/img/icons/world... https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/world.png — 200 — 3.1 KiB — 440 ms — http/1.1https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/email.png/lab_website-static/img/icons/email... https://bridgeslab.sph.umich.edu/lab_website-static/img/icons/email.png — 200 — 1.5 KiB — 453 ms — http/1.1https://www.googletagmanager.com/gtag/js?id=G-HLFFK9ZMJEwww.googletagmanager.com/gtag/js?id... https://www.googletagmanager.com/gtag/js?id=G-HLFFK9ZMJE — 200 — 145.9 KiB — 667 ms — h2https://connect.facebook.net/en_US/sdk.jsconnect.facebook.net/en_US/sdk.js https://connect.facebook.net/en_US/sdk.js — 200 — 5.0 KiB — 19 ms — h3https://cdn.jsdelivr.net/npm/bootstrap-icons@1.11.0/font/fonts/bootstrap-icons.woff2?1bb88866b4085542c8ed5fb61b9393ddcdn.jsdelivr.net/npm/bootstrap-icon... https://cdn.jsdelivr.net/npm/bootstrap-icons@1.11.0/font/fonts/bootstrap-icons.woff2?1bb88866b4085542c8ed5fb61b9393dd — 200 — 128.2 KiB — 21 ms — h2https://connect.facebook.net/en_US/bundle/sdk.js/connect.facebook.net/en_US/bundle/s... https://connect.facebook.net/en_US/bundle/sdk.js/ — 200 — 78.5 KiB — 17 ms — h3https://www.google-analytics.com/g/collect?v=2&tid=G-HLFFK9ZMJE&gtm=45je6562v9125023284za200zd9125023284&_p=1778414866692&gcd=13l3l3l3l1l1&npa=0&dma=0&are=1&cid=1688872908.1778414867&frm=0&pscdl=noapi&rcb=2&sr=800x600&uaa=x86&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uam=&uamb=0&uap=macOS&uapv=10.15.7&uaw=0&ul=en-us&_s=1&tag_exp=0~115616985~115938465~115938468~118463262&sid=1778414866&sct=1&seg=0&dl=https%3A%2F%2Fbridgeslab.sph.umich.edu%2F&dt=Bridges%20Lab%20Homepage&en=page_view&_fv=1&_nsi=1&_ss=1&_ee=1&tfd=3460www.google-analytics.com/g/collect?... https://www.google-analytics.com/g/collect?v=2&tid=G-HLFFK9ZMJE&gtm=45je6562v9125023284za200zd9125023284&_p=1778414866692&gcd=13l3l3l3l1l1&npa=0&dma=0&are=1&cid=1688872908.1778414867&frm=0&pscdl=noapi&rcb=2&sr=800x600&uaa=x86&uab=64&uafvl=Not-A.Brand%3B24.0.0.0%7CChromium%3B146.0.7680.164&uam=&uamb=0&uap=macOS&uapv=10.15.7&uaw=0&ul=en-us&_s=1&tag_exp=0~115616985~115938465~115938468~118463262&sid=1778414866&sct=1&seg=0&dl=https%3A%2F%2Fbridgeslab.sph.umich.edu%2F&dt=Bridges%20Lab%20Homepage&en=page_view&_fv=1&_nsi=1&_ss=1&_ee=1&tfd=3460 — 204 — 555 B — 417 ms — h2https://umich.edu/favicon.icoumich.edu/favicon.ico https://umich.edu/favicon.ico — 200 — 2.1 KiB — 40 ms — h2
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
50% of JavaScript execution is third-party
First-party Third-party 79ms · 146KB · $1/mo
Google Tag Manager
Tag Manager
Optional
Execution 79ms
Transfer 146 KB
Unused 43%
Monthly Cost $1/mo

50% 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

How third-party costs are calculated

Real-User Performance (CrUX)
Field metrics from the Chrome User Experience Report
INFO

Chrome User Experience (CrUX)

Real-user metrics from the Chrome UX Report (2026-04-11 — 2026-05-08)

LCP (p75)

2821 ms

70% good

INP (p75)

37 ms

99% good

CLS (p75)

0.000

82% good

FCP (p75)

2796 ms

TTFB (p75)

1485 ms

Image Optimization
7 images, 62 KB total, 51 KB wasted
INFO

Image Optimization Audit

Total Images

7

Total Size

62 KB

Oversized

1

Wasted

51 KB

7 missing dimensions 4 missing lazy loading
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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