Data version

A data version, also known as a world version, is a positive integer used in world save data to denote a specific version.

Usage
Upon selecting and loading a singleplayer world, the game will check if the client has a data version newer or older than the selected world. If it does, the game will then prompt the user whether they want to back up their world before playing it if the world is older, or warn them that their world map become corrupted if the world is newer.

Versioning
Every version of Java Edition since 15w32a, including minor releases and snapshots, has its own data version. The version takes the form of an ever-increasing positive integer, unlike client versions which have different parts of the version separated by periods ( . ). Data versions are necessary because client versions usually cannot be directly compared since they use different formats (i.e., "1.14" and "19w02a" cannot be compared). Data versions may skip numbers between major releases.

Storage location
The data version is stored in two places inside the level.dat file of a world save: in the root compound named  and also in the  compound named.
 * level.dat
 * : Information about the level.dat file.
 * : An integer displaying the data version.
 * : Versioning information about when the world was last saved.
 * : An integer displaying the data version.

Each Minecraft build also specifies its current data version in the version.json file, found in the root directory of the client and official server jars.
 * version.json
 * : The data version of this build.