Environment
|
|
| Site |
https://leetcode-py.wisl.dev (custom domain, Mintlify hosted) |
| Plan |
Free |
| Theme |
mint |
| Features in use |
docs content only. No analytics, no Assistant (locked on free), no Widget, no personalization |
| Lighthouse |
13.4.1, mobile emulation, simulated throttling |
| PageSpeed Insights |
67 mobile / 86 desktop |
Symptoms
Static documentation page with zero interactivity scores 67 on mobile. Metrics from a local Lighthouse run on the production site:
| Metric |
Value |
| FCP |
3.1s |
| LCP |
8.4s (simulated) / 2.3s observed |
| TBT |
150ms |
| CLS |
0 |
| Speed Index |
5.6s |
| TTI |
8.5s |
| Total transfer |
1.2MB across 61 requests |
Root cause analysis
1. Core bundle ships loaders for features that are not configured
/_next/static/chunks/62d7203315893733.js is 683KB uncompressed (175KB over the wire). It contains SDK loaders for posthog, plausible, fathom, kapa, Assistant UI, and MCP surfaces. This site has none of them enabled, but the code ships and executes anyway. Lighthouse reports 180KB unused JavaScript. Total script weight is around 700KB for a page that renders server-side and needs no client state.
2. Fonts preloaded unconditionally
Three woff2 files (150KB, including PaperMono variable) are preloaded in <head> on every page. Preload gives them highest priority, so they compete with the LCP image for bandwidth on throttled connections.
3. Render-blocking CSS
One 67KB stylesheet blocks first paint. The Lighthouse render-blocking audit reports 750ms wasted.
4. LCP image gets no priority hints
The actual LCP element on our landing page is a content hero image served from mintcdn.com. Tracing shows:
lcpLoadDelay = 1.8s- No
<link rel="preconnect" href="https://mintcdn.com"> anywhere in the document
- No
fetchpriority="high" on the LCP image (Lighthouse lcp-discovery: fetchpriority=high should be applied: false)
- Meanwhile Mintlify preloads both nav logo SVG variants (light and dark), one of which is always hidden by CSS
So the browser spends its preload budget on decorative logos while the LCP image discovers its CDN origin cold, mid page load.
Workarounds attempted (all limited or unavailable)
docs.json has no head field, so a preconnect or LCP preload cannot be injected.search config only accepts a placeholder prompt; there is no way to disable search to shed its JS.- Added
fetchpriority="high" loading="eager" on the hero <img> in MDX. Helps only if the platform does not strip it.
<link rel="preconnect"> in MDX body. Relies on React hoisting, not guaranteed.- Checked every dashboard settings page (Search, Assistant, Add-ons, General): no bundle, font, or performance controls exist.
The platform cost is identical on the free plan and paid plans, and none of it is opt-out.
Requests
- Feature-flag the core chunk. Split analytics loaders, Assistant, and MCP surfaces into lazy chunks loaded only when the corresponding feature is configured. An empty-config docs site should not ship or execute them.
- Conditional font preload, or a
font-display: optional fallback so fonts stop competing with LCP.
- LCP-aware hints for hosted sites: preconnect to
mintcdn.com and preload only the visible logo variant. Better, expose a head array in docs.json so customers can add their own preconnect and preload tags.
- Guidance: if any plan or theme config reduces the bundle (lighter theme, disabled features), document it. Happy to test.
Reproduce
bunx lighthouse https://leetcode-py.wisl.dev/ --output=json \
--output-path=/tmp/lh.json --only-categories=performance \
--chrome-flags="--headless=new" --form-factor=mobile --screenEmulation.mobile
Or paste the URL into pagespeed.web.dev. The unused-JS audit points at the chunk named above.
Environment
mintSymptoms
Static documentation page with zero interactivity scores 67 on mobile. Metrics from a local Lighthouse run on the production site:
Root cause analysis
1. Core bundle ships loaders for features that are not configured
/_next/static/chunks/62d7203315893733.jsis 683KB uncompressed (175KB over the wire). It contains SDK loaders for posthog, plausible, fathom, kapa, Assistant UI, and MCP surfaces. This site has none of them enabled, but the code ships and executes anyway. Lighthouse reports 180KB unused JavaScript. Total script weight is around 700KB for a page that renders server-side and needs no client state.2. Fonts preloaded unconditionally
Three woff2 files (150KB, including PaperMono variable) are preloaded in
<head>on every page. Preload gives them highest priority, so they compete with the LCP image for bandwidth on throttled connections.3. Render-blocking CSS
One 67KB stylesheet blocks first paint. The Lighthouse render-blocking audit reports 750ms wasted.
4. LCP image gets no priority hints
The actual LCP element on our landing page is a content hero image served from
mintcdn.com. Tracing shows:lcpLoadDelay= 1.8s<link rel="preconnect" href="https://mintcdn.com">anywhere in the documentfetchpriority="high"on the LCP image (Lighthouselcp-discovery:fetchpriority=high should be applied: false)So the browser spends its preload budget on decorative logos while the LCP image discovers its CDN origin cold, mid page load.
Workarounds attempted (all limited or unavailable)
docs.jsonhas noheadfield, so a preconnect or LCP preload cannot be injected.searchconfig only accepts a placeholder prompt; there is no way to disable search to shed its JS.fetchpriority="high" loading="eager"on the hero<img>in MDX. Helps only if the platform does not strip it.<link rel="preconnect">in MDX body. Relies on React hoisting, not guaranteed.The platform cost is identical on the free plan and paid plans, and none of it is opt-out.
Requests
font-display: optionalfallback so fonts stop competing with LCP.mintcdn.comand preload only the visible logo variant. Better, expose aheadarray indocs.jsonso customers can add their own preconnect and preload tags.Reproduce
bunx lighthouse https://leetcode-py.wisl.dev/ --output=json \ --output-path=/tmp/lh.json --only-categories=performance \ --chrome-flags="--headless=new" --form-factor=mobile --screenEmulation.mobileOr paste the URL into pagespeed.web.dev. The unused-JS audit points at the chunk named above.