Introduction

Sekai takes chunk-level deduplicated snapshots of Minecraft Java region files (.mca) and rebuilds the world from any snapshot quickly. It is built for frequent hot-recovery — rewinding a live server after griefing or a bad update — rather than long-term archival.

Identical chunk payloads are stored once and shared across snapshots via content-addressed storage, so an unchanged backup costs roughly one metadata row instead of a full world copy. Rollback reproduces the exact bytes captured for the snapshot, atomically and verbatim.

Sekai ships two things:

• the sekai CLI documented in this guide,
• a reusable Rust library (sekai-app over sekai-core) for server-management software. The library API is documented with rustdoc (cargo doc); this book covers operating the CLI only.

Design background lives in ARCHITECTURE.md: layering, the two-layer hashing model, and the MVCC/GC data model. The machine-readable output contract lives in docs/json.md.