Skip to content
https://www.impots.gouv.fr

Performance

· 16 checks — Lighthouse + waterfall + sustainability rolled into one auditable list.
SCORE
89
GRADE
B
FIX
1
REVIEW
3
PASS
10
INFO
2

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

Mobile Desktop
79
Performance Overall performance score (0–100) based on Core Web Vitals and other metrics. 90+ is good.
100
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.
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.

3.27 s

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

3.95 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.

0.002

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

4.43 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.

3.96 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
16
10 PASS 3 REVIEW 1 FIX
D
JS Execution Cost
Action
2086ms total JS execution
FIX
2086ms total JS execution
Warning::
https://www.impots.gouv.fr/accueil: 862ms CPU time
Warning::
Unattributable: 531ms CPU time
Warning::
https://www.impots.gouv.fr/libraries/dsfr/dist/dsf...: 513ms CPU time
Info::
https://www.impots.gouv.fr/sites/default/files/js/...: 114ms CPU time
Info::
https://www.impots.gouv.fr/sites/default/files/css...: 66ms CPU time
Info::
Third-party scripts: 531ms (25% of total)

Main Thread Breakdown

Other 36% Style & Layout 27% Script Evaluation 17% Rendering 13% Parse HTML & CSS 5%
ScriptTotalScriptingParse/CompileParty
https://www.impots.gouv.fr/accueil862ms5ms1ms1st
Unattributable531ms8ms0ms3rd
https://www.impots.gouv.fr/libraries/dsfr/dist/dsfr.module.js?td4kq3513ms198ms1ms1st
https://www.impots.gouv.fr/sites/default/files/js/js_EedQbQLNY6jc1Mye-z0lP8m3cFVGsW1V4fhEqJ9K4s4.js?scope=header&delta=0&language=fr&theme=pus_dsfr&include=eJw1iFEOgCAMxS5E3JEIuqFLkJE30esbUX_atK17ZM-gB6H9ZacAyuJjSS8CTZW06jGOS8Ky0atwyZwNO32eWFOx9QZ68CPP114ms98ms12ms1st
https://www.impots.gouv.fr/sites/default/files/css/css_uJEoZcHWZvlXb4bIm22-kteWi7ndhbVJdVME4VrQSVw.css?delta=1&language=fr&theme=pus_dsfr&include=eJxNjFEKw0AIRC-0ZI8UjJrsFhtFY-jevqSlpD_zmAczqM6VPA1kgge8Cv4J6iC6FYGheczUA_VkH1V3RpVi4LA5WIvf4DZT7paL9GhMxTJmitXrFXe7zrwTx0cFg2OrX5QYcfCzLhD8BmTfP9466ms0ms0ms1st
B
Page Weight Budget
1.1 MB transferred, 53 requests
REVIEW
1.1 MB transferred, 53 requests
Info::
Page weighs 2.5 MB (1.1 MB transferred)
Info::
53 HTTP requests
Info::
Estimated 0.22 g CO2 per page load
1.1 MB / 2.4 MB budget
1.1 MB transferred
53 requests
0.22 g CO2 per page load
Images 476.9 KiB 44%
CSS 181.7 KiB 17%
Fonts 168.5 KiB 15%
JavaScript 152.1 KiB 14%
HTML 92.2 KiB 8%
Other 17.5 KiB 2%
Other 999 B 0%
0 2.4 MB 4.9 MB
Under budget
C
Image Optimization
Action
32 images, 0 KB saveable
REVIEW
32 images, 0 KB saveable
Warning::
https://www.impots.gouv.fr/sites/default/files/med... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.impots.gouv.fr/sites/default/files/med... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.impots.gouv.fr/sites/default/files/med... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
Warning::
https://www.impots.gouv.fr/www2/code_cabcom/css/ps... is missing width/height — may cause layout shift
Set explicit width and height to prevent CLS.
32 images 477 KB
0 oversized -0 KB
29 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+
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 (14.1 KiB of 1.1 MiB)
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+
Font Loading
4 fonts (169 KB)
PASS
4 fonts (169 KB)
Info::
4 font(s) use font-display: swap (FOUT risk but functional)

Web fonts

4

169 KB total

Render-blocking

0

of 4

Dominant font-display

swap

Most common across fonts

Font loading timeline
Transfer FOIT (block) FOUT (swap)
0 ms 1.0 s 2.0 s 3.0 s 4.0 s FCP 3.3 s LCP 3.9 shttps://www.impots.gouv.fr/libraries/dsfr/dist/fonts/Marianne-Regular.woff2Marianne-Regular.woff2 https://www.impots.gouv.fr/libraries/dsfr/dist/fonts/Marianne-Regular.woff2 — 41.1 KiB — 0 ms — font-display: swaphttps://www.impots.gouv.fr/libraries/dsfr/dist/fonts/Marianne-Bold.woff2Marianne-Bold.woff2 https://www.impots.gouv.fr/libraries/dsfr/dist/fonts/Marianne-Bold.woff2 — 41.8 KiB — 0 ms — font-display: swaphttps://www.impots.gouv.fr/libraries/dsfr/dist/fonts/Marianne-Medium.woff2Marianne-Medium.woff2 https://www.impots.gouv.fr/libraries/dsfr/dist/fonts/Marianne-Medium.woff2 — 41.7 KiB — 0 ms — font-display: swaphttps://www.impots.gouv.fr/libraries/dsfr/dist/fonts/Marianne-Regular_Italic.woff2Marianne-Regular_Italic... https://www.impots.gouv.fr/libraries/dsfr/dist/fonts/Marianne-Regular_Italic.woff2 — 44.0 KiB — 0 ms — font-display: swap
Marianne-Regular.woff2 woff2 swap
Size 41 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
Marianne-Bold.woff2 woff2 swap
Size 42 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
Marianne-Medium.woff2 woff2 swap
Size 42 KB
Load time 0 ms
Start 0 ms
Risk FOUT — text flashes from fallback to web font
Marianne-Regular_Italic... woff2 swap
Size 44 KB
Load time 0 ms
Start 0 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
6 scripts, 48 KB unused
PASS
6 scripts, 48 KB unused
Warning::
https://www.impots.gouv.fr/sites/default/files/js/...: 25 KB unused (82%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.impots.gouv.fr/libraries/dsfr/dist/dsf...: 23 KB unused (50%)
Consider code splitting or tree shaking to reduce unused code.
Warning::
https://www.impots.gouv.fr/libraries/dsfr/dist/dsf...: unminified — 10 KB could be saved
Info::
Total unused JavaScript: 48 KB
48 KB unused JavaScript

Downloaded but never executed on this page.

ScriptSizeUnusedMinifiedParty
https://www.impots.gouv.fr/sites/default/files/js/js_YE3ZZj9pyOEL8oVHi4MzlDLWceT05WU6K7fXWJFsW9U.js?scope=footer&delta=0&language=fr&theme=pus_dsfr&include=eJw1iFEOgCAMxS5E3JEIuqFLkJE30esbUX_atK17ZM-gB6H9ZacAyuJjSS8CTZW06jGOS8Ky0atwyZwNO32eWFOx9QZ68CPP31 KB25 KB (82%)✓1st
https://www.impots.gouv.fr/libraries/dsfr/dist/dsfr.module.js?td4kq346 KB23 KB (50%)✗1st
https://www.impots.gouv.fr/sites/default/files/js/js_e5P7IvQEZEmTqk4r9fpjbgpDTeYGpTbnjFqhq_K6P54.js?scope=footer&delta=2&language=fr&theme=pus_dsfr&include=eJw1iFEOgCAMxS5E3JEIuqFLkJE30esbUX_atK17ZM-gB6H9ZacAyuJjSS8CTZW06jGOS8Ky0atwyZwNO32eWFOx9QZ68CPP22 KB—✓1st
https://www.impots.gouv.fr/sites/default/files/js/js_UqDPpfAcYkt3Vj9otY9f5FuhDZgAaySXKJGZQ0NClcM.js?delta=0&include=eJw1iFEOgCAMxS5E3JEIuqFLkJE30esbUX_atK17ZM-gB6H9ZacAyuJjSS8CTZW06jGOS8Ky0atwyZwNO32eWFOx9QZ68CPP&language=fr&scope=header&theme=pus_dsfr39 KB—✓1st
https://bmly.impots.gouv.fr/fuF559.js?214 KB—✓3rd
https://bmly.impots.gouv.fr/col571a/-/1626139227?pggrp=accueil&urlp=15_accueil&url=https%3A%2F%2Fwww.impots.gouv.fr%2Faccueil&sd=24&ss=412x823&fra=0&evariant=2-4&0 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

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+
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=0, s-maxage=300, public, must-revalidate, proxy-revalidate
PASS
max-age=0, s-maxage=300, public, must-revalidate, proxy-revalidate
Info::
Cache-Control header is set
Got: max-age=0, s-maxage=300, public, must-revalidate, proxy-revalidate
Info::
CDN TTL: 5 minutes (s-maxage=300)
Info::
ETag present — enables conditional (304) responses
Info::
Last-Modified header present
Cache-Control

max-age=0, s-maxage=300, public, must-revalidate, proxy-revalidate

DirectiveValueMeaning
max-age0Cache for 0 seconds
s-maxage300CDN caches for 5 minutes
public—Any cache may store this response
must-revalidate—Must recheck with server after expiry
proxy-revalidate—
Network Waterfall
53 requests over 0ms
INFO

Performance analysis not available for this result.

Third-Party Script Cost
Per-script blocking time, transfer cost, and cache headers
INFO
25% of JavaScript execution is third-party
First-party Third-party 531ms · 0KB · €6/mo
Unattributable
Other
Costly
Execution 531ms
Transfer 0 KB
Monthly Cost €6/mo

These scripts may cost more than they're worth

  • Unattributable adds 531ms and costs ~€6/month

Unattributable takes 531ms 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.

Send Feedback