---
title: "Frames are dropped while scrolling (smooth/scroll-jank)"
description: "smooth/scroll-jank: When the main thread cannot produce a frame every 16.7 ms, scrolling stutters."
canonical: https://void-design.vercel.app/rules/smooth/scroll-jank
lastModified: 2026-09-16
---

# Frames are dropped while scrolling

`smooth/scroll-jank` · severity **warn** · category Smoothness · detected by `void smooth` and `void audit`

## Why it matters

When the main thread cannot produce a frame every 16.7 ms, scrolling stutters. Users read this as a cheap, broken site even when load metrics are good.

## How to fix it

Remove work from scroll handlers (use IntersectionObserver or CSS scroll-driven animations), avoid layout reads/writes per frame, and animate only transform/opacity.

## Example

```
const io = new IntersectionObserver(([e]) => el.classList.toggle('in', e.isIntersecting));
io.observe(el);
```

## References

- https://web.dev/articles/rendering-performance

## More smoothness rules

`void smooth` reports 13 rules in this category. How the page feels after it loads: dropped frames during a scripted scroll, long animation frames, INP of real clicks, shifts after input, animated layout properties, idle rAF loops and reduced-motion handling.

- `long-frames-during-scroll` Long animation frames block scrolling — [smooth/long-frames-during-scroll](https://void-design.vercel.app/rules/smooth/long-frames-during-scroll)
- `scroll-listener-nonpassive` Non-passive wheel/touch listener — [smooth/scroll-listener-nonpassive](https://void-design.vercel.app/rules/smooth/scroll-listener-nonpassive)
- `inp-slow` Interactions are slow to respond (INP) — [smooth/inp-slow](https://void-design.vercel.app/rules/smooth/inp-slow)
- `layout-shift-after-input` Layout shifts long after an interaction — [smooth/layout-shift-after-input](https://void-design.vercel.app/rules/smooth/layout-shift-after-input)
- `layout-shift-on-scroll` Layout shifts while scrolling — [smooth/layout-shift-on-scroll](https://void-design.vercel.app/rules/smooth/layout-shift-on-scroll)
- `animate-layout-property` Animation of a layout-triggering property — [smooth/animate-layout-property](https://void-design.vercel.app/rules/smooth/animate-layout-property)
- `transition-all` transition: all — [smooth/transition-all](https://void-design.vercel.app/rules/smooth/transition-all)
- `will-change-overuse` will-change is applied too broadly — [smooth/will-change-overuse](https://void-design.vercel.app/rules/smooth/will-change-overuse)

Detected by `void smooth` and `void audit`. Explain it in a terminal: `void rules smooth/scroll-jank`