What Local-First Software Actually Means
The local-first movement promises apps that work offline, respect your data, and sync effortlessly. Here is what that actually requires to build.
Theo Nakamura
Software Engineer
The phrase "local-first" gets used in a lot of ways. Sometimes it means "works offline." Sometimes it means "your data stays on your device." It is worth being precise, because the implications for how you build software are significant.
The canonical definition comes from a 2019 paper by Martin Kleppmann and colleagues at Ink & Switch: local-first software prioritizes the local copy of your data over any server copy, while still enabling real-time collaboration. The server, in this model, is a convenience — not an authority.
Why This Matters Now
Most software today is cloud-first by default. Your documents live on Google's servers. Your notes live on Notion's servers. This works beautifully when you have an internet connection and when those companies continue to exist.
Neither of those conditions is guaranteed.
The Technical Challenges Are Real
The core challenge is conflict resolution: what happens when you edit a document on your laptop while someone else edits the same document on their phone, and neither device has internet access?
This is where CRDTs — Conflict-free Replicated Data Types — enter the picture. They are data structures designed to merge automatically without conflicts, no matter the order in which changes arrive.
What a Local-First Stack Looks Like
A local database on the device — SQLite is the common choice for mobile and desktop. A sync layer that handles conflict resolution. A server that stores a copy for backup and sharing — a peer, not a master.
The Trade-offs Nobody Advertises
Local-first is not free. You give up the simplicity of a single source of truth. You take on the complexity of eventual consistency. The point is not that local-first is always better — it is a genuine alternative with genuine advantages.