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https://zlib.net

Performance

· 17 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
97
GRADE
A+
FIX
0
REVIEW
2
PASS
13
INFO
2

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.
74
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.
92
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.

817 ms

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

817 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.

0.020

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

1.16 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.

817 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
17
13 PASS 2 REVIEW
C
Image Optimization
Action
8 images, 0 KB saveable
REVIEW
8 images, 0 KB saveable
Warning::
https://zlib.net/madler-email.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://zlib.net/zlib-email.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
8 images 45 KB
0 oversized -0 KB
8 legacy format
2 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

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

Green Hosting

No green hosting detected

A+
Page Weight Budget
59 KB transferred, 10 requests
PASS
59 KB transferred, 10 requests
Info::
Page weighs 76 KB (59 KB transferred)
Info::
10 HTTP requests
Info::
Estimated 0.01 g CO2 per page load
59 KB / 2.4 MB budget
59 KB transferred
10 requests
0.01 g CO2 per page load
Images 45.2 KiB 77%
HTML 9.5 KiB 16%
Other 4.0 KiB 7%
0 2.4 MB 4.9 MB
Under budget
A+
Third-Party Impact
No third-party resources
PASS
No third-party resources
Info::
No third-party resources detected
No third-party resources detected — all resources are first-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
279ms total JS execution
PASS
279ms total JS execution
Info::
https://zlib.net/: 176ms CPU time
Info::
Unattributable: 103ms CPU time
Info::
Third-party scripts: 103ms (37% of total)

Main Thread Breakdown

Other 44% Style & Layout 28% Rendering 19% Parse HTML & CSS 4% Script Evaluation 4%
ScriptTotalScriptingParse/CompileParty
https://zlib.net/176ms3ms1ms1st
Unattributable103ms5ms0ms3rd
A+
Font Loading
No web fonts (system fonts)
PASS
No web fonts (system fonts)
Info::
No web fonts loaded — system fonts are fastest
No web fonts loaded — system fonts are optimal.
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
10 resources · 59 KB · 0 KB savings available
PASS
10 resources · 59 KB · 0 KB savings available
Info::
Within 1MB page-weight target
Got: 59 KB
10 resources · 58.7 KiB · 0 third-party Within 1MB page-weight target
Image 84% · 49.2 KiB
Document 16% · 9.5 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+
HTTP Caching
max-age=3600 (1 hour)
PASS
max-age=3600 (1 hour)
Info::
Cache-Control header is set
Got: max-age=3600, must-revalidate
Info::
Effective TTL: 1 hour (max-age=3600)
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present
Cache-Control

max-age=3600, must-revalidate

DirectiveValueMeaning
max-age3600Cache for 1 hour
must-revalidate—Must recheck with server after expiry
Effective TTL: 3600 seconds
Network Waterfall
10 requests over 1185ms
INFO
0 ms 500 ms 1.0 s FCP 817 ms LCP 817 mshttps://zlib.net// https://zlib.net/ — 200 — 9.5 KiB — 498 ms — http/1.1https://zlib.net/images/zlib3d-b1.png/images/zlib3d-b1.png https://zlib.net/images/zlib3d-b1.png — 200 — 21.4 KiB — 172 ms — http/1.1https://zlib.net/images/zlib_ddj.png/images/zlib_ddj.png https://zlib.net/images/zlib_ddj.png — 200 — 17.3 KiB — 331 ms — http/1.1https://zlib.net/zlib-email.png/zlib-email.png https://zlib.net/zlib-email.png — 200 — 1.4 KiB — 339 ms — http/1.1https://zlib.net/images/li_blue.png/images/li_blue.png https://zlib.net/images/li_blue.png — 200 — 816 B — 485 ms — http/1.1https://zlib.net/images/li_green.png/images/li_green.png https://zlib.net/images/li_green.png — 200 — 819 B — 495 ms — http/1.1https://zlib.net/images/li_red.png/images/li_red.png https://zlib.net/images/li_red.png — 200 — 816 B — 495 ms — http/1.1https://zlib.net/images/li_yellow.png/images/li_yellow.png https://zlib.net/images/li_yellow.png — 200 — 812 B — 328 ms — http/1.1https://zlib.net/madler-email.png/madler-email.png https://zlib.net/madler-email.png — 200 — 1.9 KiB — 169 ms — http/1.1https://zlib.net/favicon.ico/favicon.ico https://zlib.net/favicon.ico — 200 — 4.0 KiB — 169 ms — http/1.1
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
37% of JavaScript execution is third-party
First-party Third-party 103ms · 0KB · $1/mo
Unattributable
Other
Optional
Execution 103ms
Transfer 0 KB
Monthly Cost $1/mo

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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