Substack Core Web Vitals
How real Chrome users experience substack.com, from Google's Chrome UX Report: the 75th percentile of visits on every device.
Substack fails Core Web Vitals
Sep 26 – Oct 23, all devices
INP
203 ms
Needs improvement
LCP
2.4 s
Good
CLS
0.02
Good
FCP
1.1 s
Good
TTFB
566 ms
Good
INP over time
Weekly p75. The dashed line is the 200 ms "good" threshold.
What the numbers say
- Substack fails Core Web Vitals on Interaction to Next Paint (203 ms, good is 200 ms or less).
- Among 14 media and community sites we track, Substack has the 8th fastest LCP.
- INP has improved by 41 ms over the last 25 weeks, from 286 ms to 245 ms.
Keep a site like this from getting slower
Real-user data shows a regression weeks after it ships. Vitalgate runs Lighthouse on every pull request and fails the check when a change breaks budgets like these: LCP ≤ 2.5 s, CLS ≤ 0.10, FCP ≤ 1.8 s.
Other media and community sites
| Site | Core Web Vitals | LCP | INP | CLS |
|---|---|---|---|---|
| YouTube | Fails | 4.7 s | 245 ms | 0.34 |
| Passes | 2.0 s | 144 ms | 0.01 | |
| X | Fails | 4.4 s | 334 ms | 0.07 |
| Fails | 2.5 s | 226 ms | 0.07 | |
| Medium | Passes | 2.4 s | 106 ms | 0.03 |
| dev.to | Passes | 1.9 s | 82 ms | 0.00 |
| Hacker News | Passes | 554 ms | 44 ms | 0.00 |
| Product Hunt | Passes | 2.2 s | 195 ms | 0.07 |
| Wikipedia | Passes | 1.2 s | 81 ms | 0.00 |
| The Verge | Fails | 1.4 s | 130 ms | 0.16 |
| Spotify | Fails | 5.9 s | 455 ms | 0.57 |
| Twitch | Fails | 3.1 s | 303 ms | 0.23 |
| Netflix | Fails | 3.7 s | 208 ms | 0.03 |