Documentation
Cronus UI compared
Cronus UI next to shadcn/ui, HeroUI, and Aceternity. It speaks the shadcn registry spec — it is not a fork. The layer above is the product: live theming, compose, a mechanical contract, and npm plus copy-in.
Side by side
Facts about distribution, theming, generation, ownership, AI, accessibility gates, and the registry protocol. No download counts.
| Dimension | Cronus UI | shadcn/ui | HeroUI | Aceternity |
|---|---|---|---|---|
| Distribution | npm package (@cronus-ui/ui) and copy-in via the CLI | Copy-in | Installed package | Copy-in (some via shadcn CLI namespace) |
| Live theming | 5 themes × light/dark, plus looks (default / brutalist / glass); CSS variables, no re-render | Utility classes you restyle | Built-in look | Tailwind / Motion, not a token runtime |
| Product generation | compose saas, store, landing + landing-* flavors; additive mail/chat/finance; upgrade without losing edits. Looks stay OSS. | You assemble | No | Marketing templates and sections, not a composed app |
| Source ownership | CLI copy-in + 3-way upgrade, incl. composed pages | Copy-in | Package lock-in | Copy-in, no 3-way upgrade |
| AI | AI Kit + MCP (hosted HTTP catalog at /mcp, stdio writes) that composes apps, adds pages, installs, and themes | Official MCP | MCP + llms.txt | Copy-prompt on components, not compose/add-page/theme |
| A11y gates | axe on catalog routes, contrast across 10 theme × mode combos, mechanical contract | Radix primitives | React Aria | Marketing-first, no CI contract |
| Registry protocol | Speaks the shadcn spec at /r/* | Is the spec | Separate | Some items via @aceternity on the shadcn CLI; separate library |
The registry is served at /r/<name>.json with the index at /r/registry.json, so a shadcn-compatible CLI can install Cronus items without forking either tool.
Where each wins
None of the four is better in every way. Pick the layer you actually need.
shadcn/ui
Wins the ecosystem and the default path for coding agents. If the job is “add a dialog the way every agent already knows,” shadcn is that protocol.
HeroUI
Wins beauty out of the box. An installed look, React Aria primitives, and a distinctive visual default with no token work required.
Aceternity
Wins motion and landing-page effects. Copy-paste React + Tailwind + Motion marketing sections — not a live token runtime, and not compose of a multi-page app.
Cronus UI
Wins theme-as-system, compose, a mechanical contract, and dual distribution. Not a shadcn fork — it speaks the spec, then layers a live theme, product generation, and 3-way upgrade of source and composed pages.