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Chunkis

Chunkis is a Fabric mod for Minecraft 1.21.11 that makes CIS (Chunk Information Storage) the authoritative persistence format for Chunkis-owned chunks.

It does not try to be a general world editor or backup system. Its job is to capture a complete enough chunk snapshot, store it safely, restore it without turning restoration into new gameplay edits, and send the restored server chunk through vanilla networking.

What happens to one changed chunk

1. Fabric mixins record mutations in a ChunkDelta attached to the live WorldChunk.
2. GlobalChunkTracker records only deltas that have an explicit Chunkis ownership claim.
3. The save path captures an authoritative snapshot and writes it to chunkis/regions/r.<x>.<z>.cis.
4. On the next load, Chunkis supplies a persisted base or synthetic load NBT to vanilla deserialization.
5. ChunkRestorer writes the saved blocks, block entities, metadata, and eligible entities into the live chunk.
6. Vanilla ChunkDataS2CPacket delivers that restored chunk to both singleplayer and remote clients.

Current storage contract

• CIS format version: 11.
• A v11 block payload is authoritative: an omitted block position restores as air.
• Sparse replay data without either a persisted vanilla base or a full block baseline is rejected rather than saved unsafely.
• Existing vanilla MCA data is imported before integrated-server startup; successful source-region retirement creates a verified .backup first.

Start here

• Architecture — module boundaries and the complete runtime flow.
• System Overview — operational behavior at save, load, client delivery, and shutdown.
• Storage Format — exact files, region layout, compression, and corruption behavior.
• Delta and Ownership Model — when a delta is authoritative and allowed to suppress vanilla writes.
• Load and Restore Pipeline — how an on-disk delta becomes a live WorldChunk.
• Migration and Versioning — CIS upgrades and vanilla MCA import rules.
• Debugging — commands and investigation workflow.
• Developer Guide — entry points, checks, and change rules.

Build

./gradlew build
./gradlew test
./gradlew runGameTest

On Windows, use gradlew.bat.

Source: Chunkis on GitHub