When Horizon won’t start, the cause is usually one of five things: an outdated launcher or graphics driver, a game that isn’t prepared from your Minecraft 26.3 files yet, a missing Java 25 for that preparation, a Vulkan problem on Windows (switch to DirectX 12), or macOS blocking an app that isn’t notarized. Find your message below. If the game does crash, the launcher shows what went wrong in one line, with buttons to open or copy the crash report.
“No version installed yet”
Nothing’s wrong; the launcher just hasn’t installed Horizon. Choose Choose a version, install the newest one on the Versions page, and go back to Play. The full first-run walkthrough is in how to install Horizon.
“Not prepared” or “Minecraft 26.3 was not found”
Horizon builds its game files from your own copy of Minecraft 26.3, once. Sign in with a Microsoft account that owns Java Edition and press Play: with no Minecraft installed, the launcher downloads 26.3 from Mojang for your account and prepares it. If you already have Minecraft somewhere unusual (a Prism or MultiMC instance, a custom folder), use Choose… next to the Minecraft folder on the Play page, then Prepare again. If the launcher can’t find it, it lists where it looked.
“Java 25 is needed”
Preparation runs vanilla’s own data generator, which is Java; the game itself isn’t. Update the launcher first: current versions use the Java the Minecraft launcher downloaded for 26.3, or download that same Java from Mojang. If it still fails (no internet during preparation, for example), install a Java 25 JDK such as Eclipse Temurin 25 and try again.
“Sign in to play”
Play stays locked until an account that owns Java Edition is signed in. Choose Open link, enter the code shown on Microsoft’s page in your browser, and the launcher continues on its own. After that you can also use an offline name.
The game crashes at start, or shows nothing
- Update the launcher and Horizon (the launcher does this on its own when it can, see below).
- Update your graphics drivers. On Linux you need a working Vulkan driver.
- On Windows, open Options → Video Settings → Advanced Graphics → Performance → Graphics API and pick DirectX 12; it applies at the next start. Auto already falls back to DirectX 12 when Vulkan has no working driver, but forcing it helps when Vulkan “works” badly.
- Check you’re on a supported system: no 32-bit builds, no ARM Linux, macOS 12 or later.
macOS: “can’t check the app” or it won’t open
The Mac app isn’t notarized by Apple. On macOS 14 and earlier, right-click Horizon, choose Open, then Open again. On macOS 15 and later, try to open it once, then go to System Settings → Privacy & Security and choose Open Anyway. Also make sure you dragged it into Applications and run it from there, not from the disk image.
The launcher never updates
A launcher can only update itself where it can write. One run from the disk image, a Mac app left in Downloads, or a Windows ZIP opened without extracting finds every update and can’t install it. Launchers 0.2.41 and older only say so in Settings, next to their version (“the update failed: …”); newer ones show Download again in the sidebar. Download the launcher once more, install it properly (drag to Applications on macOS, extract the ZIP on Windows), and it updates itself from then on. Instances, worlds and settings aren’t inside the launcher, so they stay.
It runs, but stutters
Lower the render distance, turn LOD off, or pick the Performance preset. The performance overlay (Video Settings → Advanced Graphics → Overlay) shows what’s slow. More in how to get more FPS in Horizon.
A resource pack or mod broke something
- Resource pack: switch it off on the Resource Packs screen, or move it out of
resourcepacks/. Crash reports list your active packs, which helps spot the culprit. - Content mod: a mod that fails to load shows why, in red, on its row in Options → Mods.
- Native mod: if a build fails, the launcher shows the failing step and error on the instance’s row. Many community mods are pinned to one Nightly; check each mod’s page.
- Shader pack: a pack that fails Horizon’s check is refused, with its problems in chat.
Multiplayer messages
- Realms is greyed out. Expected: Realms doesn’t work yet.
- Can’t join a public server under an offline name. Offline names only join offline-mode servers (
online-mode=false). Sign in with your Microsoft account for normal servers. - Friends can’t reach your shared world. The Play with Friends screen says what it found. If UPnP isn’t allowed, forward TCP 25580; behind CGNAT, use a VPN like Tailscale.
- Running your own server and seeing “no prepared game files” or “registries.json not found next to the resources”? See how to host a Horizon server.
Known issues in the current release
Every game release lists its current known issues in its notes, under “Known issues”; the bullets are removed in the pull request that fixes each one. In the copy of that list we took on 9 November 2026, there were no entries. Read the latest notes on our releases page before assuming your problem is new. If a fresh update broke something that worked yesterday, installing the previous Nightly is a quick workaround, as explained in Nightly or stable?
Where the logs are, and how to report a bug
Everything is in the game folder (~/.local/share/horizon, ~/Library/Application Support/horizon or %APPDATA%\horizon):
logs/latest.log: the current or last run; older runs arelogs/<date>-<number>.log.gz.crash-reports/crash-<date>_<time>-client.txt: the error, your computer and graphics card, render settings, resource packs and the last 50 log lines.
From a terminal, horizon-launcher logs --crash prints the newest crash report and horizon-launcher logs --lines 200 the end of the log.
Report on GitHub issues for horizon-rust/horizon (search first) or in the bugs channel on Horizon’s Discord. Include what you did and expected, your Horizon version (shown on the Play page) and launcher version, your system and graphics card, and the crash report or the end of latest.log. Read logs before you post: they can contain your player name, server addresses and chat. Anything that differs from vanilla 26.3 counts as a bug, so “vanilla does X and Horizon does Y” is the perfect report. Quick answers to other questions are in our FAQ.