Node WebSocket API Development

I’m finalising a mobile app built on the MERN stack and now need a specialist to take charge of the backend layer—specifically the Node.js / Express portion. My immediate priority is API development, but not the classic REST approach; I need real-time WebSocket APIs that keep client devices in constant sync without polling.

Here is what I’m after:
• Design and implement scalable WebSocket endpoints in Express
• Integrate the sockets cleanly with my existing MongoDB models
• Write clear connection, reconnection and error-handling logic
• Provide concise documentation and sample calls so my React-Native front end can consume the feed instantly
• Deliver lightweight unit tests or Postman/Insomnia collections to prove everything works

Acceptance criteria:
1. A running Express server exposing the requested WebSocket channels
2. Messages broadcast successfully to multiple connected clients with no data loss
3. Source code clean, commented and pushed to my private Git repository
4. Setup instructions that let me reproduce the environment in one go (npm install && npm start)

I have the UI/UX side largely covered, so your focus will remain on the backend plumbing, though I’m open to your suggestions if you spot any architectural gaps. If you’ve built chat, live dashboards or similar real-time features before, this should feel familiar. Let me know your timeline and any prerequisites you’ll need from me so we can get moving quickly.