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https://json.org

Performance

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

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

Mobile Desktop
97
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
67
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.
82
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.

983 ms

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

1.06 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.

0.037

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

983 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.

1.06 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
10 PASS 1 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 (217.8 KiB of 218.2 KiB)
Info::
Third-party blocking time is low (0 ms)
100%
First-party Third-party
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
7 images, 0 KB saveable
REVIEW
7 images, 0 KB saveable
Warning::
https://www.json.org/img/value.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.json.org/img/string.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.json.org/img/number.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.json.org/img/whitespace.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.json.org/img/object.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.json.org/img/array.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
7 images 171 KB
0 oversized -0 KB
7 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

A+
Page Weight Budget
218 KB transferred, 12 requests
PASS
218 KB transferred, 12 requests
Info::
Page weighs 234 KB (218 KB transferred)
Info::
12 HTTP requests
Info::
Estimated 0.04 g CO2 per page load
218 KB / 2.4 MB budget
218 KB transferred
12 requests
0.04 g CO2 per page load
Images 170.7 KiB 78%
Fonts 33.7 KiB 15%
HTML 8.9 KiB 4%
Other 4.9 KiB 2%
0 2.4 MB 4.9 MB
Under budget
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
62ms total JS execution
PASS
62ms total JS execution
Info::
https://www.json.org/json-en.html: 62ms CPU time
Warning::
Third-party scripts: 62ms (100% of total)

Main Thread Breakdown

Other 45% Style & Layout 31% Rendering 18%
ScriptTotalScriptingParse/CompileParty
https://www.json.org/json-en.html62ms1ms0ms3rd
A+
Font Loading
1 fonts (34 KB)
PASS
1 fonts (34 KB)
Info::
1 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

1

34 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 500 ms 1.0 s FCP 983 ms LCP 1.1 shttps://www.json.org/Programma-Bold.woff2Programma-Bold.woff2 https://www.json.org/Programma-Bold.woff2 — 33.7 KiB — 315 ms — font-display: swap
Programma-Bold.woff2 woff2 swap
Size 34 KB
Load time 315 ms
Start 580 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
No JavaScript
PASS
No JavaScript
Info::
No JavaScript bundles
No JavaScript files loaded.
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
12 resources · 218 KB · 0 KB savings available
PASS
12 resources · 218 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 218 KB
Warning::
10 third-party resources (100% of weight)
12 resources · 218.2 KiB · 10 third-party Within 1MB page-weight target
Image 80% · 175.5 KiB
Font 15% · 33.7 KiB
Document 4% · 8.9 KiB
Other 0% · 0 B
A+
Green Hosting
Whether the site is served from green-energy infrastructure
PASS

Green Hosting

This site is hosted on green energy infrastructure

Provider: IONOS SE

Network Waterfall
12 requests over 1133ms
INFO
0 ms 500 ms 1.0 s FCP 983 ms LCP 1.1 shttps://json.org// https://json.org/ — 200 — 386 B — 387 ms — h2https://www.json.org/json-en.htmlwww.json.org/json-en.html https://www.json.org/json-en.html — 200 — 8.5 KiB — 154 ms — h2https://json.org/favicon.ico/favicon.ico https://json.org/favicon.ico — -1 — 0 B — 156 ms — https://www.json.org/img/json160.gifwww.json.org/img/json160.gif https://www.json.org/img/json160.gif — 200 — 11.9 KiB — 161 ms — h2https://www.json.org/img/object.pngwww.json.org/img/object.png https://www.json.org/img/object.png — 200 — 19.8 KiB — 214 ms — h2https://www.json.org/img/array.pngwww.json.org/img/array.png https://www.json.org/img/array.png — 200 — 11.4 KiB — 235 ms — h2https://www.json.org/img/value.pngwww.json.org/img/value.png https://www.json.org/img/value.png — 200 — 23.6 KiB — 270 ms — h2https://www.json.org/img/string.pngwww.json.org/img/string.png https://www.json.org/img/string.png — 200 — 49.3 KiB — 411 ms — h2https://www.json.org/img/number.pngwww.json.org/img/number.png https://www.json.org/img/number.png — 200 — 36.4 KiB — 370 ms — h2https://www.json.org/Programma-Bold.woff2www.json.org/Programma-Bold.woff2 https://www.json.org/Programma-Bold.woff2 — 200 — 33.7 KiB — 315 ms — h2https://www.json.org/img/whitespace.pngwww.json.org/img/whitespace.png https://www.json.org/img/whitespace.png — 200 — 18.3 KiB — 218 ms — h2https://www.json.org/favicon.pngwww.json.org/favicon.png https://www.json.org/favicon.png — 200 — 4.9 KiB — 131 ms — h2
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 62ms · 9KB · €1/mo
www.json.org
Other
Optional
Execution 62ms
Transfer 9 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

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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