Skip to content
https://openjdk.org

Performance

· 14 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
95
GRADE
A
FIX
1
REVIEW
2
PASS
10
INFO
1

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

Mobile Desktop
100
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
57
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.
75
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.

240 ms

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

712 ms

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.

0.007

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

576 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.

712 ms

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
10 PASS 2 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
9 images, 0 KB saveable
REVIEW
9 images, 0 KB saveable
Warning::
https://openjdk.org/images/duke-chalkboard.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://openjdk.org/images/duke-plug.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://openjdk.org/images/duke-pipes.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://openjdk.org/images/duke-thinking.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
9 images 53 KB
0 oversized -0 KB
7 legacy format
4 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

C
Green Hosting
Action
Whether the site is served from green-energy infrastructure
REVIEW

Green Hosting

No green hosting detected

A+
Page Weight Budget
295 KB transferred, 26 requests
PASS
295 KB transferred, 26 requests
Info::
Page weighs 694 KB (295 KB transferred)
Info::
26 HTTP requests
Info::
Estimated 0.06 g CO2 per page load
295 KB / 2.4 MB budget
295 KB transferred
26 requests
0.06 g CO2 per page load
JavaScript 186.8 KiB 63%
Images 52.9 KiB 18%
Fonts 42.8 KiB 15%
HTML 6.0 KiB 2%
CSS 2.8 KiB 1%
Other 2.5 KiB 1%
Other 1.3 KiB 0%
0 2.4 MB 4.9 MB
Under budget
A+
Third-Party Impact
1% third-party, 0 ms blocking
PASS
1% third-party, 0 ms blocking
Info::
Third-party code accounts for 1% of page weight (3.1 KiB of 295.1 KiB)
Info::
Third-party blocking time is low (0 ms)
99%
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+
JS Execution Cost
175ms total JS execution
PASS
175ms total JS execution
Info::
https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fi...: 175ms CPU time

Main Thread Breakdown

Script Evaluation 67% Other 17% Style & Layout 7% Script Parsing & Compilation 5%
ScriptTotalScriptingParse/CompileParty
https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbzJb3i0N8h7Dip/SF4jOnQD/bgpa/ViQeFBEB175ms144ms12ms1st
A+
Font Loading
2 fonts (43 KB)
PASS
2 fonts (43 KB)
Info::
2 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

2

43 KB total

Render-blocking

0

of 2

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 500 ms 1.0 s FCP 240 ms LCP 712 mshttps://openjdk.org/.fonts/DejaVuSans-webfont.woffDejaVuSans-webfont.woff https://openjdk.org/.fonts/DejaVuSans-webfont.woff — 21.4 KiB — 19 ms — font-display: swaphttps://openjdk.org/.fonts/DejaVuSans-Bold-webfont.woffDejaVuSans-Bold-webfont... https://openjdk.org/.fonts/DejaVuSans-Bold-webfont.woff — 21.4 KiB — 21 ms — font-display: swap
DejaVuSans-webfont.woff woff swap
Size 21 KB
Load time 19 ms
Start 706 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
DejaVuSans-Bold-webfont... woff swap
Size 21 KB
Load time 21 ms
Start 708 ms
Risk FOUT — text flashes from fallback to web font
  • Convert to woff2 for ~30% smaller file size
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 ~13 KB and ~26 ms

A+
JS Bundles
5 scripts, 37 KB unused
PASS
5 scripts, 37 KB unused
Warning::
https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fi...: 37 KB unused (21%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 37 KB
37 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbzJb3i0N8h7Dip/SF4jOnQD/bgpa/ViQeFBEB174 KB37 KB (21%)✓1st
https://openjdk.org/page.js1 KB—✓1st
https://cdn.usefathom.com/script.js3 KB—✓3rd
https://openjdk.org/akam/13/3ce02fab9 KB—✓1st
blob:https://openjdk.org/a5a0c945-4048-4e66-a342-bb1c2795c5130 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

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+
Page Weight Inventory
26 resources · 295 KB · 37 KB savings available
PASS
26 resources · 295 KB · 37 KB savings available
Info::
Within 1MB page-weight target
Got: 295 KB
Info::
8 third-party resources (1% of weight)
26 resources · 295.1 KiB · 8 third-party Within 1MB page-weight target
JavaScript 63% · 186.8 KiB
Image 18% · 54.2 KiB
Font 15% · 42.8 KiB
Document 2% · 6.6 KiB
CSS 1% · 2.8 KiB
Other 1% · 1.9 KiB

~37.0 KiB of savings available

Remove unused JavaScript: 37.0 KiB
Network Waterfall
26 requests over 2035ms
INFO
0 ms 500 ms 1.0 s 1.5 s 2.0 s FCP 240 ms LCP 712 mshttps://openjdk.org// https://openjdk.org/ — 200 — 6.0 KiB — 228 ms — h2https://openjdk.org/page.css/page.css https://openjdk.org/page.css — 200 — 1.6 KiB — 185 ms — h2https://openjdk.org/page.js/page.js https://openjdk.org/page.js — 200 — 1.1 KiB — 15 ms — h2https://openjdk.org/images/openjdk2.svg/images/openjdk2.svg https://openjdk.org/images/openjdk2.svg — 200 — 2.3 KiB — 29 ms — h2https://openjdk.org/images/duke-thinking.png/images/duke-thinking.png https://openjdk.org/images/duke-thinking.png — 200 — 14.8 KiB — 30 ms — h2https://openjdk.org/images/duke-plug.png/images/duke-plug.png https://openjdk.org/images/duke-plug.png — 200 — 11.7 KiB — 14 ms — h2https://openjdk.org/images/duke-chalkboard.png/images/duke-chalkboard.png https://openjdk.org/images/duke-chalkboard.png — 200 — 8.8 KiB — 27 ms — h2https://openjdk.org/images/duke-pipes.png/images/duke-pipes.png https://openjdk.org/images/duke-pipes.png — 200 — 12.6 KiB — 30 ms — h2https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbzJb3i0N8h7Dip/SF4jOnQD/bgpa/ViQeFBEB/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbz... https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbzJb3i0N8h7Dip/SF4jOnQD/bgpa/ViQeFBEB — 200 — 173.7 KiB — 34 ms — h2https://cdn.usefathom.com/script.jscdn.usefathom.com/script.js https://cdn.usefathom.com/script.js — 200 — 2.7 KiB — 8 ms — h2https://openjdk.org/akam/13/3ce02fab/akam/13/3ce02fab https://openjdk.org/akam/13/3ce02fab — 200 — 9.3 KiB — 9 ms — h2https://openjdk.org/images/oracle.svg/images/oracle.svg https://openjdk.org/images/oracle.svg — 200 — 2.3 KiB — 48 ms — h2https://openjdk.org/.fonts/dejavu.css/.fonts/dejavu.css https://openjdk.org/.fonts/dejavu.css — 200 — 1.2 KiB — 187 ms — h2https://openjdk.report-uri.io/r/default/csp/reportOnlyopenjdk.report-uri.io/r/default/csp... https://openjdk.report-uri.io/r/default/csp/reportOnly — -1 — 0 B — 101 ms — https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbzJb3i0N8h7Dip/SF4jOnQD/bgpa/ViQeFBEB/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbz... https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbzJb3i0N8h7Dip/SF4jOnQD/bgpa/ViQeFBEB — 201 — 944 B — 198 ms — h2https://openjdk.org/.fonts/DejaVuSans-webfont.woff/.fonts/DejaVuSans-webfont.woff https://openjdk.org/.fonts/DejaVuSans-webfont.woff — 200 — 21.4 KiB — 19 ms — h2https://openjdk.org/.fonts/DejaVuSans-Bold-webfont.woff/.fonts/DejaVuSans-Bold-webfont.wof... https://openjdk.org/.fonts/DejaVuSans-Bold-webfont.woff — 200 — 21.4 KiB — 21 ms — h2data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAASwAAACWCAYAAABkW7XSAAAQAElEQVR4AeycCZhUxbXHT3UPMwg4q…data:image/png;base64,iVBORw0KGgoAA... data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAASwAAACWCAYAAABkW7XSAAAQAElEQVR4AeycCZhUxbXHT3UPMwg4q… — 200 — 0 B — 0 ms — datadata:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAACGFjVEwAAAABAAAAAcMq2TYAAAANS…data:image/png;base64,iVBORw0KGgoAA... data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAACGFjVEwAAAABAAAAAcMq2TYAAAANS… — 200 — 0 B — 0 ms — datahttps://openjdk.report-uri.io/r/default/csp/reportOnlyopenjdk.report-uri.io/r/default/csp... https://openjdk.report-uri.io/r/default/csp/reportOnly — -1 — 0 B — 23 ms — https://cdn.usefathom.com/?h=https%3A%2F%2Fopenjdk.org&p=%2F&r=&sid=KCYJJPZX&qs=%7B%7D&cid=76072009cdn.usefathom.com/?h=https%3A%2F%2F... https://cdn.usefathom.com/?h=https%3A%2F%2Fopenjdk.org&p=%2F&r=&sid=KCYJJPZX&qs=%7B%7D&cid=76072009 — 200 — 432 B — 124 ms — h2https://openjdk.org/images/nanoduke.ico/images/nanoduke.ico https://openjdk.org/images/nanoduke.ico — 200 — 1.3 KiB — 22 ms — h2https://openjdk.org/akam/13/pixel_3ce02fab/akam/13/pixel_3ce02fab https://openjdk.org/akam/13/pixel_3ce02fab — 200 — 584 B — 21 ms — h2https://openjdk.report-uri.io/r/default/csp/reportOnlyopenjdk.report-uri.io/r/default/csp... https://openjdk.report-uri.io/r/default/csp/reportOnly — -1 — 0 B — 21 ms — blob:https://openjdk.org/a5a0c945-4048-4e66-a342-bb1c2795c513openjdk.org/a5a0c945-4048-4e66-a342... blob:https://openjdk.org/a5a0c945-4048-4e66-a342-bb1c2795c513 — -1 — 0 B — 0 ms — https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbzJb3i0N8h7Dip/SF4jOnQD/bgpa/ViQeFBEB/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbz... https://openjdk.org/3AaSu3zE/qBvsWf4/ZlJ9obh/Hu/fiapbzJb3i0N8h7Dip/SF4jOnQD/bgpa/ViQeFBEB — 201 — 984 B — 278 ms — h2
HTML JavaScript CSS Images Fonts XHR/Fetch Other
All checks on this page are automated. Results are estimates - run targeted manual reviews when the score affects a release decision.

Send Feedback