cn

cn is a new engine for Tailwind class merging and conflict resolution. It replaces tailwind-merge and clsx. Same APIs. Full parity. And it is 30× faster.

import { cn } from "cn"

// conditional joining (like clsx) + conflict resolution (like tailwind-merge)
cn("px-2 py-1", isActive && "bg-blue-500", { "text-white": isActive })

cn has zero dependencies and is framework-agnostic: it works with React, Vue, Svelte, Solid, Astro, or plain server templates, and runs in browsers, Node, Bun, Deno, and edge runtimes. It works in any Tailwind CSS project. You don't need shadcn/ui.

cn is built and maintained by aidenybai and shadcn.

Can I use this today?

Yes. You can replace tailwind-merge and clsx with cn today. It's a drop-in replacement.

Here's a command to migrate:

npx shadcn@latest migrate cn

Install

npm i cn

New project

Import it and go. Nothing to configure:

import { cn } from "cn"

export function Button({
  className,
  active,
  ...props
}: React.ComponentProps<"button"> & { active?: boolean }) {
  return (
    <button
      className={cn(
        "rounded-md px-4 py-2 text-sm",
        active && "bg-primary",
        className
      )}
      {...props}
    />
  )
}

Existing shadcn/ui project

Using the shadcn CLI

npx shadcn@latest migrate cn

Manually

Your components already import cn from @/lib/utils. Replace the wrapper with the one from cn.

// lib/utils.ts
- import { clsx, type ClassValue } from "clsx";
- import { twMerge } from "tailwind-merge";

- export function cn(...inputs: ClassValue[]) {
-   return twMerge(clsx(inputs));
- }
+ export { cn } from "cn";

Then remove clsx and tailwind-merge from your dependencies. If other packages still import them, alias them to cn so your bundle only carries one implementation.

How much faster?

The following benchmarks compare cn against clsx + tailwind-merge, which is what most projects run today.

We ran each library through every workload in its own isolated process with its own warmup, and kept the best of 5 runs.

To see the results for yourself, run pnpm bench. The methodology is in docs/how-it-works.md.

scenario	clsx + tailwind-merge	cn	faster
the call your components make most¹	320 ns	10 ns	30×
same classes as last render (cache hit)	14 ns	7 ns	1.9×
typical component strings, warm	13 ns	7 ns	1.9×
thousands of recurring strings (a real repo's working set)	2.4 µs	14 ns	172×
cold render, many arbitrary values	3.4 µs	1.1 µs	3.0×
cold render, SSR-style unique strings	2.3 µs	360 ns	6.4×
very first call (page load)	3.2 ms	0.4 ms	7×

¹ cn(base, variant, condition && extra) with stable class strings. This is the shape almost every component call has. cn learns repeated call sequences, so a render loop's calls verify by identity and skip the work entirely.

Real repositories

The rows above are synthetic. pnpm bench:corpus replays every cn() call harvested from 58 open source codebases (144,265 calls) through each library, one isolated process per library and repository, and prints the per-repository table. Geometric mean across the 58 repositories: cn is 37× faster than clsx + tailwind-merge.

cn ships the least JavaScript to parse in every setup, 26 KB minified.

If you want an even smaller bundle with the same performance, see cn build.

Custom themes

cn/config accepts the same { extend, override, prefix } shape, under the same name:

// before
import { extendTailwindMerge } from "tailwind-merge"

const twMerge = extendTailwindMerge({
  extend: { classGroups: { "font-size": [{ text: ["hero"] }] } },
})

// after
import { createCn } from "cn/config"

const cn = createCn({
  extend: { classGroups: { "font-size": [{ text: ["hero"] }] } },
})

Custom validator functions work as-is. fromTheme, validators, mergeConfigs, and defaultConfig are exported from cn/config. Tailwind v4 prefixes are supported: createCn({ prefix: "tw" }).

Coming from tailwind-merge

cn produces the same output as tailwind-merge for every input. We verify this with 356,000 differential tests.

Every export maps to the same name or a familiar one:

tailwind-merge	cn
twMerge(...)	twMerge(...) from "cn", identical
twJoin(...)	twJoin(...) from "cn", identical
extendTailwindMerge(ext)	same name, from "cn/config"
createTailwindMerge(fn)	createTwMerge(fn) from "cn/config"
getDefaultConfig()	defaultConfig() from "cn/config"
fromTheme, validators	same names, from "cn/config"
mergeConfigs	same name, from "cn/config"
experimentalParseClassName	not supported

Gotchas

• cn supports Tailwind CSS v4, like tailwind-merge v3. On Tailwind v3, stay with tailwind-merge v2.
• Classes that merely look like Tailwind utilities (text-2xs) are treated as Tailwind utilities. Same behavior and guidance as tailwind-merge's docs.
• With cn build, dynamically constructed class names ("p-" + size) can't be detected. Same rule as Tailwind itself. Use --safelist.
• The CLI needs Node 20+.

API

• cn: cn(...inputs), twMerge(...), twJoin(...), clsx(...)
• cn/config: createCn(ext?), extendTailwindMerge(ext?), createTwMerge(ext?), fromTheme, validators, defaultConfig(), mergeConfigs(base, ext)
• cn/engine: createCn(tables, ...), createEngine(tables, ...) for build-time compiled tables
• cn/lite: clsx(...), strings-only join (clsx/lite parity)
• cn/build: build(options), the library behind the CLI, for custom pipelines and bundler plugins
• CLI: npx cn build --help

Credits

• cn's merge engine, compiler, and table format are original work.
• The package's conflict-resolution semantics intentionally match those of tailwind-merge by Dany Castillo (MIT licensed), and the default tables it ships are compiled from tailwind-merge's default configuration.
• The clsx-compatible join layer implements the argument semantics of clsx by Luke Edwards (MIT licensed).
• The argument-identity cache for repeated variadic calls re-implements an optimization pioneered by cnfast by Aiden Bai (MIT licensed).

Thank you to all three authors.