Real-time collaborative editing has become a standard feature in modern web applications. Yjs provides a robust CRDT (Conflict-free Replicated Data Type) implementation that handles the complex synchronization logic, while Next.js 15 offers the perfect foundation for building performant full-stack applications. This combination enables developers to create production-ready collaborative editors with minimal infrastructure complexity.

Yjs implements CRDTs to enable conflict-free merging of concurrent edits from multiple users. Unlike operational transformation (OT), which requires a central server to resolve conflicts, CRDTs allow each client to independently merge changes without coordination. This architecture provides better offline support and reduces server load.

The library works by tracking changes at a granular level—individual character insertions, deletions, and formatting changes. When multiple users edit the same document simultaneously, Yjs automatically resolves conflicts using its CRDT algorithms. The result is eventual consistency across all connected clients without requiring complex server-side logic.

Next.js 15 introduces several improvements for real-time applications, including enhanced Server Actions and improved WebSocket support. The architecture requires both client-side collaborative editing and server-side state synchronization.

For the WebSocket server, Next.js custom server setup works well with the y-websocket provider:

Building the Collaborative Editor Component

ProseMirror provides a solid foundation for rich text editing. The integration with Yjs happens through the y-prosemirror binding, which synchronizes ProseMirror's document state with Yjs's shared type.

Implementing Persistence with Server Actions

Next.js 15 Server Actions provide a clean way to persist document snapshots. While Yjs handles real-time synchronization, periodic snapshots ensure data durability and faster initial loads for new clients.

The WebSocket server can be enhanced to load initial state and periodically save snapshots:

Handling Offline Support and Conflict Resolution

One significant advantage of Yjs is built-in offline support. The library automatically queues changes made while disconnected and merges them when connection resumes. However, developers should implement proper UI feedback for offline states.

The y-indexeddb provider enables local persistence:

For applications requiring strict ordering or validation, consider implementing a middleware layer that validates changes before broadcasting. This adds latency but prevents invalid states:

Yjs performs well for documents up to several thousand concurrent operations. For larger documents, consider implementing document sharding—splitting content into multiple Yjs documents based on logical sections.

Memory usage scales with document history. The garbage collection option (gc: true) removes tombstones from deleted content, but this prevents clients from syncing if they've been offline for extended periods. The trade-off depends on the application's requirements:

- Enable GC for applications where users rarely work offline for extended periods

- Disable GC for applications requiring full history preservation or frequent offline work

WebSocket connection limits become relevant at scale. A single Node.js process handles approximately 10,000-15,000 concurrent WebSocket connections. Beyond this threshold, implement horizontal scaling with a message broker like Redis:

The combination of Next.js 15 and Yjs provides a robust foundation for collaborative editing. The CRDT approach eliminates complex server-side conflict resolution while maintaining strong consistency guarantees. For production deployments, implement proper monitoring for WebSocket connections, document size metrics, and sync latency to identify bottlenecks early.

Tutorials

Building Real-Time Collab Editors with Next.js 15 & Yjs