If you have ever opened a Minecraft world folder, you have seen files ending in .mca — names like r.0.0.mca inside a folder called region. Those files are where a Java Edition world actually keeps its terrain. This page explains what an .mca file is, how the files in a world folder fit together, and why tools like MCA Selector work the way they do.
The short answer
An .mca file is a region file in Minecraft’s Anvil storage format (the extension is short for “Minecraft Anvil”). One region file holds a grid of 32 × 32 chunks — an area of 512 × 512 blocks — including the blocks, heightmaps and chunk-level data for that part of the world. The coordinates in the file name tell you which region of the world it covers: r.0.0.mca is the region at region coordinates 0, 0. Region coordinates are chunk coordinates divided by 32.
One world, three kinds of region files
Chunk data is not all stored in one place. A Java Edition world folder keeps three sibling folders of .mca files, and a complete backup or copy of a world needs all three:
region— the terrain itself: blocks, biomes, structures and the chunk data MCA Selector renders as its top-down map.entities— entity data for the same chunks (mobs, item frames, dropped items and similar), stored in its own set of region files with matching coordinates.poi— points-of-interest data for the same chunks, such as the blocks villagers and other game systems track.
Each dimension keeps its own set of these folders. This is also why MCA Selector asks you to open the world folder itself — the folder that directly contains region or poi — and reports “No Dimensions found” when you point it one level too high or too deep.
Where level.dat fits in
Not everything lives in .mca files. The world folder also holds level.dat, the world’s central data file, which stores world-level information rather than terrain — things like world settings and player data. The division of labour is simple: level.dat describes the world, the .mca files contain the world. Editing tools reflect that split: MCA Selector operates on the region, poi and entities files, while a raw NBT editor such as NBTExplorer is the tool you would open level.dat itself with (see MCA Selector vs NBTExplorer).
Why the game must be closed while you edit
MCA Selector is an external tool: it reads and writes the .mca files directly on disk, outside the game. Minecraft and a running server also write to those same files. If the world is open in the game while you edit it, the game can overwrite your changes — or your changes can land in a world the game then saves over. Always close the world (and stop the server) before opening it in MCA Selector. This is also why there is no save button to forget: deletions and NBT changes are written to the .mca files immediately, as explained in why MCA Selector changes “don’t save”.
.mca is Java Edition only
The Anvil .mca format belongs to Minecraft Java Edition. Bedrock Edition stores its worlds in a LevelDB database instead, which is a completely different format — there are no region, poi or entities .mca folders in a Bedrock world. That is why MCA Selector cannot open Bedrock saves, and why the author has stated there are no plans to add Bedrock support. The full story, and what Bedrock players can use instead, is in does MCA Selector work with Bedrock?
Working with .mca files, safely
- Back up the whole world folder first — region, poi, entities and level.dat together. Deletions in MCA Selector are instant and cannot be undone. Our world backup workflow shows the local + cloud routine.
- Close the world in Minecraft and stop any server using it before editing.
- Keep the three folders together when copying or moving a world — terrain without its matching entities and poi files is an incomplete save.
Download MCA Selector 2.9
To view, select and edit the chunks inside your world’s .mca files, get the current release from the MCA Selector download page — the Windows installer, the cross-platform .jar, the macOS .dmg and the Linux .deb / .rpm packages, with SHA-256 hashes for verification. New to the tool? Start with how to use MCA Selector.
One last backup reminder: keep the copy of your world you made before editing until you have loaded the edited world in Minecraft and confirmed it looks right. Deletions and NBT changes in MCA Selector are permanent once applied.
Related guides
Go deeper on the formats and the workflows around them: