About
Environment variables an agent needs: masked secrets with reveal and copy, required keys that are missing flagged with what to do, descriptions per key, and the file they come from.
Built with React and Tailwind. Copy the prompt and paste it into Claude Code, Cursor or Lovable: your agent adds Environment Variables to your project and fits it to your theme.
Code
How Environment Variables 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 { EnvironmentVariables } from "@/components/ui/environment-variables"
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>
)
}
function EnvironmentVariablesDemo() {
return (
<div className="w-full max-w-2xl">
<EnvironmentVariables
source=".env.local"
peek
variables={[
{
key: "DATABASE_URL",
value: "postgres://checkout:x8Vq2mLr@db.internal:5432/checkout",
required: true,
description: "Primary Postgres",
},
{ key: "STRIPE_SECRET_KEY", value: "sk_test_51NqZ7kLbW3cRfE9h2YtD4f2a", required: true },
{
key: "STRIPE_WEBHOOK_SECRET",
required: true,
description: "From stripe listen, starts with whsec_",
},
{ key: "RESEND_API_KEY", required: true, description: "Receipt emails" },
{ key: "NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY", value: "pk_test_51NqZ7kLbW3cRfE9hQm0pXa" },
{ key: "NEXT_PUBLIC_SITE_URL", value: "http://localhost:3000" },
{ key: "SENTRY_DSN", description: "Optional. Errors only go to the console without it" },
]}
/>
</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 EnvironmentVariablesPreview() {
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">
<EnvironmentVariablesDemo />
</div>
<MoreOn slug="environment-variables">Env vars with masking, missing keys and copy. On</MoreOn>
</div>
</FitFrame>
)
}








