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https://json.org

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
91
GRADE
A
FIX
2
REVIEW
1
PASS
12
INFO
2

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.
67
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.
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.

2.16 s

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

2.61 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.

0.245

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

2.16 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.

2.61 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
17
12 PASS 1 REVIEW 2 FIX
D
Third-Party Impact
Action
90% third-party, 0 ms blocking
FIX
90% third-party, 0 ms blocking
Warning::
Third-party code accounts for 90% of page weight (217.8 KiB of 242.7 KiB)
Info::
Third-party blocking time is low (0 ms)
90%
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
243 KB transferred, 12 requests
PASS
243 KB transferred, 12 requests
Info::
Page weighs 258 KB (243 KB transferred)
Info::
12 HTTP requests
Info::
Estimated 0.05 g CO2 per page load
243 KB / 2.4 MB budget
243 KB transferred
12 requests
0.05 g CO2 per page load
Images 170.7 KiB 70%
Fonts 33.7 KiB 14%
Other 29.4 KiB 12%
HTML 8.9 KiB 4%
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
412ms total JS execution
PASS
412ms total JS execution
Info::
https://www.json.org/json-en.html: 243ms CPU time
Info::
Unattributable: 169ms CPU time
Warning::
Third-party scripts: 412ms (100% of total)

Main Thread Breakdown

Other 47% Style & Layout 26% Rendering 19% Parse HTML & CSS 5% Script Evaluation 3%
ScriptTotalScriptingParse/CompileParty
https://www.json.org/json-en.html243ms4ms1ms3rd
Unattributable169ms8ms0ms3rd
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 1.5 s 2.0 s 2.5 s FCP 2.2 s LCP 2.6 shttps://www.json.org/Programma-Bold.woff2Programma-Bold.woff2 https://www.json.org/Programma-Bold.woff2 — 33.7 KiB — 398 ms — font-display: swap
Programma-Bold.woff2 woff2 swap
Size 34 KB
Load time 398 ms
Start 735 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 · 243 KB · 0 KB savings available
PASS
12 resources · 243 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 243 KB
Warning::
10 third-party resources (90% of weight)
12 resources · 242.7 KiB · 10 third-party Within 1MB page-weight target
Image 82% · 200.1 KiB
Font 14% · 33.7 KiB
Document 4% · 8.9 KiB
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+
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 1271ms
INFO
0 ms 500 ms 1.0 s 1.5 s 2.0 s 2.5 s FCP 2.2 s LCP 2.6 shttps://json.org// https://json.org/ — 200 — 386 B — 399 ms — h2https://www.json.org/json-en.htmlwww.json.org/json-en.html https://www.json.org/json-en.html — 200 — 8.5 KiB — 274 ms — h2https://json.org/favicon.ico/favicon.ico https://json.org/favicon.ico — 200 — 24.5 KiB — 199 ms — h2https://www.json.org/img/json160.gifwww.json.org/img/json160.gif https://www.json.org/img/json160.gif — 200 — 11.9 KiB — 148 ms — h2https://www.json.org/img/object.pngwww.json.org/img/object.png https://www.json.org/img/object.png — 200 — 19.8 KiB — 177 ms — h2https://www.json.org/img/array.pngwww.json.org/img/array.png https://www.json.org/img/array.png — 200 — 11.4 KiB — 194 ms — h2https://www.json.org/img/value.pngwww.json.org/img/value.png https://www.json.org/img/value.png — 200 — 23.6 KiB — 323 ms — h2https://www.json.org/img/string.pngwww.json.org/img/string.png https://www.json.org/img/string.png — 200 — 49.3 KiB — 389 ms — h2https://www.json.org/img/number.pngwww.json.org/img/number.png https://www.json.org/img/number.png — 200 — 36.4 KiB — 284 ms — h2https://www.json.org/img/whitespace.pngwww.json.org/img/whitespace.png https://www.json.org/img/whitespace.png — 200 — 18.3 KiB — 378 ms — h2https://www.json.org/Programma-Bold.woff2www.json.org/Programma-Bold.woff2 https://www.json.org/Programma-Bold.woff2 — 200 — 33.7 KiB — 398 ms — h2https://www.json.org/favicon.pngwww.json.org/favicon.png https://www.json.org/favicon.png — 200 — 4.9 KiB — 132 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 412ms · 9KB · €4/mo
www.json.org
Other
Costly
Execution 243ms
Transfer 9 KB
Monthly Cost €3/mo
Unattributable
Other
Optional
Execution 169ms
Transfer 0 KB
Monthly Cost €2/mo

These scripts may cost more than they're worth

  • www.json.org adds 243ms and costs ~€3/month

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

www.json.org takes 243ms 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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