Yjs in Next.js 16, tRPC, and shadcn/ui

Yjs 13.6.31 in an App Router codebase — the decisions collaborative editing forces and how to settle them, written so an agent applies them while writing or reviewing code. Each rule names the wrong default it corrects; there is no rule for things the model already gets right.

Most of these failures are silent. Yjs converges, the editor keeps working, and the data loss surfaces later as "my change reverted" — so the rules below lead with the evidence of the failure, most of it measured directly against Yjs 13.6.31 rather than asserted.

When to Apply

• Building collaborative editing, presence, or offline sync into a Next.js 16 App Router app
• Choosing shared types for a document model, or reviewing one that loses edits under concurrency
• Deciding where the sync backend runs, or wiring tRPC procedures alongside a Yjs provider
• Persisting Y.Doc state to a database, or compacting stored updates
• Binding a Yjs document to React — provider lifecycle, subscriptions, Strict Mode, SSR
• Wiring Tiptap or shadcn/ui form controls to a live document
• Debugging a document that syncs but duplicates, blanks, or reverts content

This skill does not cover general Next.js App Router patterns (use the nextjs skill), general tRPC usage (trpc), or shadcn/ui component conventions (shadcn) — only where those intersect with a CRDT.

Version Pin