Questions
Is it free?
Yes. SpawnLoft is open source under the MIT licence, and the desktop app is a free download. There is no paid tier, no account and nothing to unlock. If it earns its keep, there is a Sponsor button.
Can my friends join?
Anyone on your home network can join straight away with your PC's local address and the server's port. Anyone outside it needs a way in, and that is the one thing SpawnLoft deliberately does not do for you. Opening a port on your router, or running a tunnel such as playit.gg, is a decision about exposing your machine to the internet, and it should be yours. See Security. A Share screen that lays those options out honestly is on the roadmap.
Does it work on Mac or Linux?
The desktop app is Windows only for now. The command line underneath runs anywhere Node does, apart from the scheduler, which speaks to Windows Task Scheduler. Other platforms are on the roadmap.
Do I need to install Java?
Yes, and it is the one thing SpawnLoft cannot do for you, because a Minecraft server is a Java program. Current Minecraft needs Java 25; 1.21 runs on 21, and older versions on 17. The app checks for Java on first run and links the download if it is missing. Each server picks the Java it needs from what is installed, so a 1.20 server and a current one can run side by side.
Which servers can it run?
Paper, Purpur, Folia, Advanced Slime Paper, vanilla, Spigot, CraftBukkit, Fabric and NeoForge, or a whole modpack from Modrinth. The server software page has the details, including which ones load plugins and which load mods.
Can I use a server I already have?
Yes. Add one I already have points SpawnLoft at the folder. Nothing is moved or rewritten; the ports and RCON password are read from its own server.properties. Removing it from SpawnLoft later leaves the folder exactly where it was.
Does closing the window stop my server?
No. Servers are detached processes that do not belong to the window. Close it, sign back in tomorrow, and they are still running with their consoles intact.
Where is my data?
In folders on your disk. Servers, worlds, backups and the jar store live in the data folder, which Settings can move. Nothing is uploaded anywhere.
Windows says "Windows protected your PC"
The installer is signed, but SmartScreen judges by reputation, and a new publisher earns that through real installs. Click More info, then Run anyway. It goes away on its own as the reputation builds.
Is it safe to leave the panel open?
The panel only answers the machine it runs on, and refuses requests from any page that is not itself, port included. There is no way to bind it to another address. See Security for exactly what leaves the machine, which is two things, both on a click.
Something broke. Where do I report it?
Feedback → Something broke in the panel opens a GitHub issue with the version, Java, server status and panel log already filled in. For a server that will not start, the troubleshooting page covers the failures SpawnLoft recognises.