Skip to content
https://www.julialang.org

Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
80
GRADE
B
FIX
2
REVIEW
3
PASS
9
INFO
2

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

Mobile Desktop
55
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.
92
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.

13.98 s

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

18.19 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.

0.044

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

13.98 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.

18.29 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
9 PASS 3 REVIEW 2 FIX
F
Page Weight Budget
Action
3.9 MB transferred, 49 requests
FIX
3.9 MB transferred, 49 requests
Warning::
Page weighs 7.3 MB (3.9 MB transferred)
Info::
Fonts are 2.0 MB — consider subsetting or using system fonts
Subset fonts to include only used characters, or switch to system font stacks.
Got: 2.0 MB
Warning::
JavaScript is 853 KB — consider code splitting or lazy loading
Large JavaScript bundles delay interactivity. Split code by route or defer non-critical scripts.
Got: 853 KB
Info::
49 HTTP requests
Info::
Estimated 0.81 g CO2 per page load
3.9 MB / 2.4 MB budget
3.9 MB transferred
49 requests
0.81 g CO2 per page load
Fonts 2.0 MiB 52%
JavaScript 853.3 KiB 21%
Images 782.4 KiB 20%
CSS 140.2 KiB 4%
HTML 87.3 KiB 2%
Other 18.7 KiB 0%
Other 18.1 KiB 0%
Other 3.1 KiB 0%
Other 0 B 0%
0 2.4 MB 4.9 MB
Over budget

Subset fonts to include only used characters, or switch to system font stacks.

Why this matters

Font payload is large — subset to used glyphs only, or fall back to system fonts (zero load time).

Source: web.dev font loading

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
Third-Party Impact
Action
80% third-party, 0 ms blocking
FIX
80% third-party, 0 ms blocking
Warning::
Third-party code accounts for 80% of page weight (3.1 MiB of 3.9 MiB)
Info::
Third-party blocking time is low (0 ms)
20%
80%
First-party Third-party
C
Image Optimization
Action
14 images, 0 KB saveable
REVIEW
14 images, 0 KB saveable
Warning::
is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.julialang.org/assets/infra/minesweeper... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.julialang.org/assets/infra/parallel-pr... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.julialang.org/assets/infra/cartpole.we... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.julialang.org/assets/infra/lorenz.gif is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
14 images 782 KB
0 oversized -0 KB
7 legacy format
5 missing dimensions CLS risk

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

C
JS Execution Cost
Action
1133ms total JS execution
REVIEW
1133ms total JS execution
Warning::
https://www.julialang.org/: 554ms CPU time
Warning::
Unattributable: 381ms CPU time
Info::
https://plausible.io/js/script.js: 138ms CPU time
Info::
https://www.youtube.com/s/player/57fefa84/www-widg...: 61ms CPU time
Warning::
Third-party scripts: 579ms (51% of total)

Main Thread Breakdown

Style & Layout 40% Other 38% Script Evaluation 11% Rendering 7%
ScriptTotalScriptingParse/CompileParty
https://www.julialang.org/554ms10ms2ms1st
Unattributable381ms5ms0ms3rd
https://plausible.io/js/script.js138ms14ms1ms3rd
https://www.youtube.com/s/player/57fefa84/www-widgetapi.vflset/www-widgetapi.js61ms44ms3ms3rd
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+
Font Loading
4 fonts (2066 KB)
PASS
4 fonts (2066 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

2066 KB total

Render-blocking

0

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 2.0 s 4.0 s 6.0 s 8.0 s 10.0 s 12.0 s 14.0 s 16.0 s 18.0 s FCP 14.0 s LCP 18.2 shttps://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 36.7 KiB — 0 ms — font-display: swaphttps://cdn.jsdelivr.net/gh/cormullion/juliamono-webfonts/JuliaMono-Bold.woff2JuliaMono-Bold.woff2 https://cdn.jsdelivr.net/gh/cormullion/juliamono-webfonts/JuliaMono-Bold.woff2 — 997.8 KiB — 0 ms — font-display: swaphttps://cdn.jsdelivr.net/gh/cormullion/juliamono-webfonts/JuliaMono-Regular.woff2JuliaMono-Regular.woff2 https://cdn.jsdelivr.net/gh/cormullion/juliamono-webfonts/JuliaMono-Regular.woff2 — 997.4 KiB — 0 ms — font-display: swaphttps://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v48/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 33.9 KiB — 0 ms — font-display: swap
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 37 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
JuliaMono-Bold.woff2 woff2 swap
Size 998 KB
Load time 0 ms
Start 0 ms
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
JuliaMono-Regular.woff2 woff2 swap
Size 997 KB
Load time 0 ms
Start 0 ms
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
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 34 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 ~998 KB and ~1996 ms

A+
JS Bundles
14 scripts, 0 KB unused
PASS
14 scripts, 0 KB unused
0 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.julialang.org/libs/detectdark.js1 KB—✓1st
https://www.julialang.org/libs/buttons.js7 KB—✓1st
https://plausible.io/js/script.js2 KB—✓3rd
https://kit.fontawesome.com/f030d443fe.js0 KB—✓3rd
https://www.julialang.org/libs/youtube-player.js1 KB—✓1st
https://www.julialang.org/libs/bootstrap/bootstrap.bundle.min.js24 KB—✓1st
https://www.julialang.org/libs/highlight/highlight.min.js17 KB—✓1st
https://www.julialang.org/libs/carousel.js1 KB—✓1st
https://www.youtube.com/iframe_api4 KB—✓3rd
https://www.youtube.com/s/player/57fefa84/www-widgetapi.vflset/www-widgetapi.js11 KB—✓3rd
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
7 hints, 0 missing preconnects
PASS
7 hints, 0 missing preconnects
Info::
Page uses 7 resource hint(s)

Current Resource Hints

preconnect
2
preload
2
dns-prefetch
3
prefetch
—

7 resource hints configured

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
A+
HTTP Caching
max-age=600 (10 minutes)
PASS
max-age=600 (10 minutes)
Info::
Cache-Control header is set
Got: max-age=600
Info::
Effective TTL: 10 minutes (max-age=600)
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present
Cache-Control

max-age=600

DirectiveValueMeaning
max-age600Cache for 10 minutes
Effective TTL: 600 seconds
Network Waterfall
49 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
51% of JavaScript execution is third-party
First-party Third-party 579ms · 12KB · $10/mo
Unattributable
Other
Costly
Execution 381ms
Transfer 0 KB
Monthly Cost $7/mo
Plausible Analytics
Analytics
Optional
Execution 138ms
Transfer 2 KB
Monthly Cost $2/mo
www.youtube.com
Other
Optional
Execution 61ms
Transfer 11 KB
Monthly Cost $1/mo

These scripts may cost more than they're worth

  • Unattributable adds 381ms and costs ~$7/month

51% 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 381ms 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.

Send Feedback