About
Package upgrades an agent suggests: old and new version, the kind of release with a warning for majors, what changed, license and size, and the install command to copy.
Built with React and Tailwind. Copy the prompt and paste it into Claude Code, Cursor or Lovable: your agent adds Package Info to your project and fits it to your theme.
Code
How Package Info is used: the demo's code. The component's own source comes with a free account.
Usage.tsx
"use client"
import * as React from "react"
import { PackageInfo } from "@/components/ui/package-info"
const FIT_CSS = "html,body{overflow:hidden}[data-fit-small] [data-fit-hide]{display:none!important}"
/**
* 21st shows a demo in a small frame: about 674 by 421 on a component page, 358 by 224 on a
* phone and 245 by 139 on a profile card. A demo taller than its frame gets scrollbars, which
* render white on dark pages. FitFrame fills the frame exactly instead.
*
* - "scale": the content shrinks until it fits, centered. For visuals such as orbs.
* - "crop": the content stays at full size from the top and fades out at the bottom. For text
* that streams in, where a changing scale would make the page breathe.
*
* `minWidth` lays out a wide demo (a table, a two column panel) at that width and scales it down
* to the frame, instead of letting it collapse to a narrow layout. The frame centers it, so it
* shrinks evenly on both sides.
*
* Anything marked `data-fit-hide` (state buttons, the chatcn.dev line) drops out in frames
* shorter than `hideBelow`, so a profile card shows the visual alone.
*/
function FitFrame({
children,
mode = "scale",
hideBelow = 360,
minWidth,
}: {
children: React.ReactNode
mode?: "scale" | "crop"
hideBelow?: number
minWidth?: string
}) {
const content = React.useRef<HTMLDivElement>(null)
const [cropped, setCropped] = React.useState(false)
React.useLayoutEffect(() => {
const el = content.current
if (!el) return
const measure = () => {
const vw = window.innerWidth
const vh = window.innerHeight
el.toggleAttribute("data-fit-small", vh < hideBelow)
// Layout sizes ignore the transform, so measuring never feeds back.
const w = Math.max(el.offsetWidth, el.scrollWidth)
const h = Math.max(el.offsetHeight, el.scrollHeight)
const scale = mode === "scale" ? Math.min(1, vw / w, vh / h) : 1
el.style.transform = scale < 1 ? `scale(${scale})` : ""
setCropped(mode === "crop" && h > vh + 1)
}
measure()
const observer = new ResizeObserver(measure)
observer.observe(el)
// Content that changes inside a fixed width box (a headline that cycles words) never resizes
// the box itself, so changes below it measure again on the next frame.
let frame = 0
const mutations = new MutationObserver(() => {
cancelAnimationFrame(frame)
frame = requestAnimationFrame(measure)
})
mutations.observe(el, { subtree: true, childList: true, characterData: true })
window.addEventListener("resize", measure)
return () => {
observer.disconnect()
mutations.disconnect()
cancelAnimationFrame(frame)
window.removeEventListener("resize", measure)
}
}, [mode, hideBelow])
const fade = "linear-gradient(to bottom, #000 calc(100% - 40px), transparent)"
return (
<div
className="flex w-full justify-center overflow-hidden"
style={{
height: "100dvh",
alignItems: mode === "crop" ? "flex-start" : "center",
maskImage: cropped ? fade : undefined,
WebkitMaskImage: cropped ? fade : undefined,
}}
>
<style>{FIT_CSS}</style>
<div
ref={content}
className="w-full shrink-0"
style={{ transformOrigin: mode === "crop" ? "top center" : "center", minWidth }}
>
{children}
</div>
</div>
)
}
/** An agent upgrades the schema library across a major version and says what came with it. */
function PackageInfoDemo() {
return (
<div className="flex w-full max-w-lg flex-col gap-3">
<PackageInfo
name="zod"
previousVersion="3.24.2"
version="4.1.5"
description="TypeScript first schema validation. Version 4 changes error formatting and how unknown keys are stripped."
dependencies={[{ name: "@zod/core", version: "0.11.6", change: "added" }]}
license="MIT"
size={13_900}
href="https://www.npmjs.com/package/zod"
command="pnpm add zod@4.1.5"
/>
<PackageInfo
name="date-fns"
previousVersion="4.1.0"
version="4.1.1"
description="Fixes the week number at year boundaries."
license="MIT"
size={17_200}
command="pnpm add date-fns@4.1.1"
/>
</div>
)
}
/** The line under each 21st demo that points back to the kit. */
function MoreOn({ slug, children }: { slug: string; children: React.ReactNode }) {
return (
<p data-fit-hide className="text-[0.75rem]/[1rem] text-(color:--chatcn-fg-faint) text-center text-balance">
{children}{" "}
<a
href={`https://chatcn.dev/docs/components/${slug}`}
target="_blank"
rel="noopener"
className="text-(color:--chatcn-fg-subtle) hover:text-(color:--chatcn-fg) underline underline-offset-2"
>
chatcn.dev
</a>
</p>
)
}
/** The kit's own example, framed for the 21st preview. */
export default function PackageInfoPreview() {
return (
<FitFrame minWidth="38rem">
<div className="flex w-full flex-col items-center justify-center gap-4 p-6">
<div className="flex w-full max-w-2xl justify-center">
<PackageInfoDemo />
</div>
<MoreOn slug="package-info">Package upgrades with breaking change notes. On</MoreOn>
</div>
</FitFrame>
)
}








