Building Signal: Lessons from Real-Time

Signal started as an internal tool — a place for our small team to share asynchronous updates without the noise of Slack. It grew into something we wanted to share with the world.

Building real-time features is deceptively complex. WebSocket connections, conflict resolution, optimistic updates — each layer adds new failure modes. This case study documents our journey, the mistakes we made, and the patterns that finally worked.

The biggest lesson: real-time isn't about speed, it's about trust. Users need to trust that what they see is accurate. Speed is a means to that end, not the end itself.