UI libraries
The React-component-library landscape post-shadcn — the map for “which kit, and why now.”
The shadcn inversion (the load-bearing fact)
shadcn/ui changed the distribution model, not the components: copy-and-own — no npm dependency, the source lands in your repo. npx shadcn add made component libraries registries instead of packages. Consequences that define the whole 2025–26 generation:
- Owning the source = styling is yours to break; Tailwind tokens and primitives (Radix UI, now also Base UI) became the compat layer, not the framework
- Registries compose: any kit can ship as a shadcn registry (install via
npx shadcn add @vendor/component) - The differentiator moved to what’s on top: more primitives, real dashboard compositions (not isolated demos), docs, and — the 2026 layer — agent fluency
The field
- shadcn/ui — the substrate; primitives + the registry protocol everyone targets
- reui (OSS) (keenthemes, 3.6k★ MIT; captured 2026-10-08 via shuxer’s cron-jobs-for-ReUI teaser, 371❤) — “design-forward shadcn platform with MCP fluency for agents”: 24 in-house primitives base shadcn lacks (Data Grid on TanStack Table v9 + Virtual, Event Calendar, Gantt, Kanban, Cascader, Tree, Timeline…), 1,175 free registry components across 83 categories shown in realistic dashboard layouts, dual Radix/Base UI builds, all Shadcn-Create themes (Vega/Nova/Maia/Lyra/Mira). The agent layer is the tell: free MCP server + agent skill — “connect any coding agent (Claude, Codex, Cursor, v0, Lovable, Replit, OpenCode, VS Code, Zed) to the ReUI registry for live search, real component APIs and one-command installs” — plus agent-shaped components (Code Block “for AI chat and streaming agent output,” Marker for “agent run logs, inline status lines”). Pro/Ultimate unlock blocks/templates on the same foundation.
- The adjacent moves the same week: v0/Lovable-class generators consuming registries directly; Excalidraw shipping an official CLI “for humans and agents” — UI kits are becoming agent-accessible products (registry + MCP + docs-as-API), the frontend chapter of Agent-accessible product.
Selection heuristics
- Count the primitives you actually need (data grid / calendar / gantt are the expensive ones — ReUI’s 24 exist because base shadcn lacks them)
- Registry compatibility beats npm packages — copy-and-own or walk away
- Docs quality = component quality in this ecosystem; realistic-layout docs (ReUI’s stance) predict production fit better than isolated demos
- Agent fluency is now a feature column: MCP server, agent skill, streaming/AI-chat-shaped components
- License tier usually splits free components from composed blocks — the free tier staying MIT is the health signal
Vault kin
- Agent-accessible product — registries + MCP + docs-as-API as the frontend chapter
- CLIs for agents — the same JSON-default/agent-first surface, GUI side
- Concepts visualization — the render/annotate loop that consumes these kits’ output