Playing Your Vanilla Worlds in Horizon Launcher

A launcher that orphaned your old worlds would be a curiosity, not a tool. The build from the Horizon Launcher app keeps saves in the vanilla format, so your library simply moves with you. This guide covers the round trip, the upgrades, and the two habits that keep a shared library safe.

The round trip: Java to Horizon and back

Worlds created in the Java game open in Horizon, and worlds played in Horizon open back in the Java game, because both clients read and write the same save format. Paletted chunk storage, region files and save data are shared ground, verified by the project harnesses like everything else.

That makes the Java client a permanent second opinion: any world that worries you can be checked there in minutes. the content mods guide explains how the modded world exception works, because content mods are the one thing vanilla does not know.

Old worlds upgrade the vanilla way

Worlds from 1.8 through 26.2 upgrade in Horizon the same way the vanilla game upgrades them, superflat worlds included, with old options and hotbar data carried along. An archive world is not a museum piece here; it is a playable save.

Upgrade thoughtfully anyway: open a copy of a truly precious old world first if the original matters historically. The upgrade path is proven, and prudence with irreplaceable things is still free. the versions guide shows how a spare archive build makes even that caution easy.

Two habits for a healthy shared library

First, keep modded worlds labelled with their mod list, since their content depends on definitions vanilla lacks. Second, let one client finish saving before the other opens the same world; the format is shared, but simultaneous cooks spoil any broth.

Follow those two and a library can live in both clients for years, which is precisely the relationship the Horizon project designed for.

Tested on our own Android phones with the current build, like every guide on this site. If a step behaves differently on your device, tell us through the contact page and the guide gets corrected, not defended.