// the find
cBournhonesque/lightyear
A networking library to make multiplayer games for the Bevy game engine
Lightyear is a server-authoritative networking library for Bevy that handles the hard parts of multiplayer: client-side prediction with rollback, snapshot interpolation, lag compensation, and interest management. It targets Rust game developers building real-time multiplayer games who don't want to implement QUIC transport, tick synchronization, and input buffering from scratch. WASM support via WebTransport is a genuine differentiator.
The prediction/rollback system is first-class — you opt in per-component with a one-line change, and the library handles the tick history, correction blending, and re-simulation automatically. Transport layer is genuinely pluggable: UDP, WebTransport, WebSocket, Steam, and an in-process crossbeam channel for testing, all behind the same abstraction. The workspace is well-decomposed into focused crates (connection, replication, inputs, IO) rather than one monolith, which keeps compile times manageable and makes it possible to understand one subsystem without reading everything. Bandwidth management with priority-based send ordering is included — most game netcode libraries leave this to you.
The book is marked WIP and it shows: advanced topics like interest management and authority transfer have sparse prose, and you will end up reading source code and examples rather than docs. Bevy version coupling is tight — each minor Bevy release requires a new Lightyear version, and the ecosystem is still at 0.x, so breaking changes land frequently; adopting this mid-project means planning for upgrade churn. The Steam transport is a separate community-adjacent concern and the SteamWorks SDK integration adds a non-trivial native dependency that makes CI and cross-platform builds messier. Deterministic replication support is there but the simulation determinism requirement is entirely on you — floats, third-party physics, and any non-deterministic Bevy system will silently break it with no guardrails.