Skip to content
https://yaml.org

Performance

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

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

Mobile Desktop
99
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
93
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.
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.

475 ms

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

1.02 s

Total Blocking Time Total Blocking Time — total time the main thread was blocked, preventing user input. Under 200ms is good.

32 ms

Cumulative Layout Shift Cumulative Layout Shift — measures visual stability. How much the page layout shifts during loading. Under 0.1 is good.

0.000

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

475 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.

1.02 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 2 REVIEW 1 FIX
D
Third-Party Impact
Action
81% third-party, 0 ms blocking
FIX
81% third-party, 0 ms blocking
Warning::
Third-party code accounts for 81% of page weight (326.1 KiB of 404.2 KiB)
Info::
Third-party blocking time is low (0 ms)
19%
81%
First-party Third-party
B
JS Bundles
5 scripts, 122 KB unused
REVIEW
5 scripts, 122 KB unused
Warning::
https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml...: 122 KB unused (49%)
Consider code splitting or tree shaking to reduce unused code.
Info::
Total unused JavaScript: 122 KB
122 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js251 KB122 KB (49%)✓3rd
https://polyfill.io/v3/polyfill.min.js?features=es60 KB—✓3rd
https://yaml.org/assets/javascripts/bundle.50899def.min.js33 KB—✓1st
https://yaml.org/js/mathjax.js3 KB—✓1st
https://yaml.org/assets/javascripts/workers/search.d50fe291.min.js0 KB—✓1st

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

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

Green Hosting

No green hosting detected

A+
Page Weight Budget
404 KB transferred, 17 requests
PASS
404 KB transferred, 17 requests
Info::
Page weighs 1.6 MB (404 KB transferred)
Info::
17 HTTP requests
Info::
Estimated 0.08 g CO2 per page load
404 KB / 2.4 MB budget
404 KB transferred
17 requests
0.08 g CO2 per page load
JavaScript 286.7 KiB 71%
Fonts 68.7 KiB 17%
CSS 28.8 KiB 7%
Other 7.9 KiB 2%
Images 6.0 KiB 1%
HTML 5.6 KiB 1%
Other 622 B 0%
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
Image Optimization
1 images, 0 KB saveable
PASS
1 images, 0 KB saveable
Warning::
https://yaml.org/assets/logo.png is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
1 images 6 KB
0 oversized -0 KB
1 legacy format
1 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

A+
JS Execution Cost
144ms total JS execution
PASS
144ms total JS execution
Info::
https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml...: 88ms CPU time
Info::
https://yaml.org/assets/javascripts/bundle.50899de...: 56ms CPU time
Warning::
Third-party scripts: 88ms (61% of total)

Main Thread Breakdown

Script Evaluation 49% Style & Layout 19% Other 15% Script Parsing & Compilation 13%
ScriptTotalScriptingParse/CompileParty
https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js88ms64ms22ms3rd
https://yaml.org/assets/javascripts/bundle.50899def.min.js56ms26ms2ms1st
A+
Font Loading
2 fonts (69 KB)
PASS
2 fonts (69 KB)
Info::
2 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

2

69 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 475 ms LCP 1.0 shttps://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2KFO7CnqEu92Fr1ME7kSn66a... https://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 36.7 KiB — 51 ms — font-display: swaphttps://fonts.gstatic.com/s/robotomono/v31/L0x5DF4xlVMF-BfR8bXMIjhLq3-cXbKD.woff2L0x5DF4xlVMF-BfR8bXMIjh... https://fonts.gstatic.com/s/robotomono/v31/L0x5DF4xlVMF-BfR8bXMIjhLq3-cXbKD.woff2 — 32.0 KiB — 50 ms — font-display: swap
KFO7CnqEu92Fr1ME7kSn66a... woff2 swap
Size 37 KB
Load time 51 ms
Start 134 ms
Risk FOUT — text flashes from fallback to web font
L0x5DF4xlVMF-BfR8bXMIjh... woff2 swap
Size 32 KB
Load time 50 ms
Start 134 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+
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
17 resources · 404 KB · 122 KB savings available
PASS
17 resources · 404 KB · 122 KB savings available
Info::
Within 1MB page-weight target
Got: 404 KB
Info::
~122 KB of savings available
Warning::
7 third-party resources (81% of weight)
Info::
1 resources over 200KB
17 resources · 404.2 KiB · 7 third-party Within 1MB page-weight target
JavaScript 71% · 286.7 KiB
Font 17% · 68.7 KiB
CSS 7% · 28.8 KiB
Other 2% · 7.9 KiB
Image 2% · 6.6 KiB
Document 1% · 5.6 KiB

~121.7 KiB of savings available

Remove unused JavaScript: 121.7 KiB
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
17 requests over 258ms
INFO
0 ms 500 ms 1.0 s FCP 475 ms LCP 1.0 shttps://yaml.org// https://yaml.org/ — 200 — 5.6 KiB — 4 ms — h2https://yaml.org/assets/stylesheets/main.7e37652d.min.css/assets/stylesheets/main.7e37652d.m... https://yaml.org/assets/stylesheets/main.7e37652d.min.css — 200 — 22.2 KiB — 4 ms — h2https://polyfill.io/v3/polyfill.min.js?features=es6polyfill.io/v3/polyfill.min.js?feat... https://polyfill.io/v3/polyfill.min.js?features=es6 — -1 — 0 B — 21 ms — https://yaml.org/assets/stylesheets/palette.06af60db.min.css/assets/stylesheets/palette.06af60d... https://yaml.org/assets/stylesheets/palette.06af60db.min.css — 200 — 2.0 KiB — 6 ms — h2https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CRoboto+Mono:400,400i,700,700i&display=fallbackfonts.googleapis.com/css?family=Rob... https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CRoboto+Mono:400,400i,700,700i&display=fallback — 200 — 2.7 KiB — 76 ms — h2https://yaml.org/css/extra.css/css/extra.css https://yaml.org/css/extra.css — 200 — 1.8 KiB — 7 ms — h2https://yaml.org/assets/logo.png/assets/logo.png https://yaml.org/assets/logo.png — 200 — 6.0 KiB — 10 ms — h2https://yaml.org/assets/javascripts/bundle.50899def.min.js/assets/javascripts/bundle.50899def... https://yaml.org/assets/javascripts/bundle.50899def.min.js — 200 — 32.7 KiB — 10 ms — h2https://yaml.org/js/mathjax.js/js/mathjax.js https://yaml.org/js/mathjax.js — 200 — 2.7 KiB — 2 ms — h2https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.jscdn.jsdelivr.net/npm/mathjax@3/es5/... https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js — 200 — 251.1 KiB — 11 ms — h2https://yaml.org/assets/javascripts/workers/search.d50fe291.min.js/assets/javascripts/workers/search.... https://yaml.org/assets/javascripts/workers/search.d50fe291.min.js — 200 — 174 B — 32 ms — h2https://yaml.org/search/search_index.json/search/search_index.json https://yaml.org/search/search_index.json — 200 — 4.3 KiB — 3 ms — h2https://api.github.com/repos/yaml/www.yaml.org/releases/latestapi.github.com/repos/yaml/www.yaml.... https://api.github.com/repos/yaml/www.yaml.org/releases/latest — 404 — 1.1 KiB — 81 ms — h2https://api.github.com/repos/yaml/www.yaml.orgapi.github.com/repos/yaml/www.yaml.... https://api.github.com/repos/yaml/www.yaml.org — 200 — 2.5 KiB — 81 ms — h2https://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2fonts.gstatic.com/s/roboto/v51/KFO7... https://fonts.gstatic.com/s/roboto/v51/KFO7CnqEu92Fr1ME7kSn66aGLdTylUAMa3yUBHMdazQ.woff2 — 200 — 36.7 KiB — 51 ms — h3https://fonts.gstatic.com/s/robotomono/v31/L0x5DF4xlVMF-BfR8bXMIjhLq3-cXbKD.woff2fonts.gstatic.com/s/robotomono/v31/... https://fonts.gstatic.com/s/robotomono/v31/L0x5DF4xlVMF-BfR8bXMIjhLq3-cXbKD.woff2 — 200 — 32.0 KiB — 50 ms — h3https://yaml.org/assets/favicon.svg/assets/favicon.svg https://yaml.org/assets/favicon.svg — 200 — 622 B — 3 ms — h2
HTML JavaScript CSS Images Fonts XHR/Fetch Other
Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
61% of JavaScript execution is third-party
First-party Third-party 88ms · 251KB · $1/mo
jsDelivr
CDN
Optional
Execution 88ms
Transfer 251 KB
Unused 49%
Monthly Cost $1/mo

61% 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

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