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Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
91
GRADE
A
FIX
1
REVIEW
3
PASS
10
INFO
2

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

Mobile Desktop
70
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.
96
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.

2.09 s

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

5.15 s

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

54 ms

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

0.197

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

2.41 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.

5.17 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
16
10 PASS 3 REVIEW 1 FIX
D
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.
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present

No Cache-Control header

Adding a Cache-Control header can significantly improve repeat-visit performance.

C
Image Optimization
Action
28 images, 0 KB saveable
REVIEW
28 images, 0 KB saveable
Warning::
https://www.haskell.org/testimonials/logos/serokel... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://i1.ytimg.com/vi/re96UgMk6GQ/mqdefault.jpg is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/central... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/e-bot7.... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/noredin... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/stackbu... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/img/haskell-logo.svg is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://i1.ytimg.com/vi/LnX3B9oaKzw/mqdefault.jpg is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://i1.ytimg.com/vi/t1e8gqXLbsU/mqdefault.jpg is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/bitnomi... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/fission... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/iohk.pn... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://i1.ytimg.com/vi/4RuLzL_q0zs/mqdefault.jpg is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://i1.ytimg.com/vi/IzQTfh-Iuds/mqdefault.jpg is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/finn.pn... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/hubspot... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/mercury... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/Scrive.... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://i1.ytimg.com/vi/WHVMjMIJnB4/mqdefault.jpg is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/bellroy... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/calabri... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/foxhoun... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/hasura.... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/imagine... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.haskell.org/testimonials/logos/scarf.p... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
28 images 702 KB
0 oversized -0 KB
28 legacy format
25 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

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

C
JS Execution Cost
Action
1025ms total JS execution
REVIEW
1025ms total JS execution
Warning::
https://www.haskell.org/: 377ms CPU time
Warning::
Unattributable: 326ms CPU time
Info::
https://www.haskell.org/js/jquery.js: 166ms CPU time
Info::
https://cdn.jsdelivr.net/npm/glider-js@1/glider.mi...: 155ms CPU time
Info::
Third-party scripts: 482ms (47% of total)

Main Thread Breakdown

Other 35% Style & Layout 31% Script Evaluation 17% Rendering 9% Parse HTML & CSS 5%
ScriptTotalScriptingParse/CompileParty
https://www.haskell.org/377ms28ms3ms1st
Unattributable326ms6ms0ms3rd
https://www.haskell.org/js/jquery.js166ms119ms14ms1st
https://cdn.jsdelivr.net/npm/glider-js@1/glider.min.js155ms3ms1ms3rd
C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A
Page Weight Budget
858 KB transferred, 44 requests
PASS
858 KB transferred, 44 requests
Info::
Page weighs 1.1 MB (858 KB transferred)
Info::
44 HTTP requests
Info::
Estimated 0.18 g CO2 per page load
858 KB / 2.4 MB budget
858 KB transferred
44 requests
0.18 g CO2 per page load
Images 701.8 KiB 82%
Fonts 63.0 KiB 7%
JavaScript 61.9 KiB 7%
CSS 18.5 KiB 2%
HTML 11.6 KiB 1%
Other 1.5 KiB 0%
0 2.4 MB 4.9 MB
Under budget
A+
Third-Party Impact
9% third-party, 0 ms blocking
PASS
9% third-party, 0 ms blocking
Info::
Third-party code accounts for 9% of page weight (74.1 KiB of 858.2 KiB)
Info::
Third-party blocking time is low (0 ms)
91%
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
3 fonts (63 KB)
PASS
3 fonts (63 KB)
Info::
3 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

3

63 KB total

Render-blocking

0

of 3

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 2.1 s LCP 5.2 shttps://www.haskell.org/fonts/source-sans-3-v9-latin-regular.woff2source-sans-3-v9-latin-... https://www.haskell.org/fonts/source-sans-3-v9-latin-regular.woff2 — 14.9 KiB — 0 ms — font-display: swaphttps://www.haskell.org/fonts/ubuntu-mono-v15-latin-regular.woff2ubuntu-mono-v15-latin-r... https://www.haskell.org/fonts/ubuntu-mono-v15-latin-regular.woff2 — 27.0 KiB — 0 ms — font-display: swaphttps://www.haskell.org/fonts/raleway-v28-latin-700.woff2raleway-v28-latin-700.w... https://www.haskell.org/fonts/raleway-v28-latin-700.woff2 — 21.1 KiB — 0 ms — font-display: swap
source-sans-3-v9-latin-... woff2 swap
Size 15 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
ubuntu-mono-v15-latin-r... woff2 swap
Size 27 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
raleway-v28-latin-700.w... woff2 swap
Size 21 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)
A
JS Bundles
7 scripts, 0 KB unused
PASS
7 scripts, 0 KB unused
Warning::
https://www.haskell.org/js/jquery.console.js: unminified — 4 KB could be saved
0 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://cdn.jsdelivr.net/npm/glider-js@1/glider.min.js3 KB—✓3rd
https://www.haskell.org/js/jquery.js33 KB—✓1st
https://www.haskell.org/js/bootstrap.min.js8 KB—✓1st
https://www.haskell.org/js/home.js1 KB—✓1st
https://www.haskell.org/js/jquery.console.js7 KB—✗1st
https://www.haskell.org/js/tryhaskell.js3 KB—✓1st
https://www.haskell.org/js/tryhaskell.pages.js7 KB—✓1st
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+
Render-Blocking Resources
No render-blocking resources detected
PASS
No render-blocking resources detected
Info::
No render-blocking resources detected in <head>
A+
Third-Party Resources
No third-party resources detected
PASS
No third-party resources detected
Network Waterfall
44 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
47% of JavaScript execution is third-party
First-party Third-party 482ms · 3KB · $6/mo
Unattributable
Other
Costly
Execution 326ms
Transfer 0 KB
Monthly Cost $4/mo
jsDelivr
CDN
Optional
Execution 155ms
Transfer 3 KB
Monthly Cost $2/mo

These scripts may cost more than they're worth

  • Unattributable adds 326ms and costs ~$4/month

47% 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

Unattributable takes 326ms 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

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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