Turn a modded server you've already set up into shareable packs, and build a one-click installer that sets the whole pack up for your friends without them touching a single file.
The Modpack Builder takes a modded server you've already got running and turns it into something you can hand to other people. You point it at a server, it works out which mods belong where, and it gives you back ready to share packs. There are three things it can produce, a server pack for whoever's hosting, a client pack for players, and a one-click installer that sets everything up for them. You can build any mix of the three in one go.
You'll find it on the main screen under Build Modpack.
There are two ways in. If you've already got a modded server in MC Server Manager, just pick it from the list and the builder reads its mods and config straight off disk. If you're starting a pack from scratch and don't have a server yet, make a Modpack Project instead. A project is a blank workspace you can drop jars into, or browse mods into, and it runs through exactly the same build process as a real server.
Either way, click Resolve mods and the builder scans them.
Only modded Java servers can become a pack, that's Forge, Fabric, NeoForge and Quilt. Vanilla and Bedrock servers don't have mods to bundle, so they won't show up in the list.
Some mods only belong on the client, like a minimap or a sound pack. Some only belong on the server. A lot belong on both. Getting this wrong is the usual reason a pack breaks, so for every mod the builder checks a few things, the mod's own metadata, the Modrinth database, and what its dependencies need, then it picks a side.
When it can't be sure, it puts the mod on both sides so nothing goes missing, a mod that's in the wrong place but still there is much safer than one that's left out. The mods it does sort to a single side are the ones it flags for a look, since those are the ones left out of one of the packs.
If it does get one wrong, just change the side on that mod's row. The builder remembers the correction and applies it everywhere that mod turns up from then on, even after the mod updates to a newer version, so you only ever fix a mod once. A banner tells you how many mods are worth a look. You don't have to clear it, the build works fine on the safe defaults, it's just there if you want to double check.
If you're building from a Modpack Project, click Browse mods to add more. It searches CurseForge and Modrinth together and locks the version to your pack's Minecraft version, so you can't accidentally grab a build that won't load. For a pack based on an existing server, add or remove mods on the server's own Mods tab first, then Resolve again.
Tick whichever you want before you hit build. They all land in a Modpacks folder on your Desktop.
Server pack. A zip for whoever's hosting. It bundles the server-side mods, your config and your server.properties, plus a start script that installs the right loader on first run and then launches the server. They unzip it and run start.bat or start.sh, no manual loader setup needed.
Client pack. A zip for players. It's self-contained, the actual mod jars plus config, so anyone can drop it into a game directory and play. No CurseForge app or extra tools needed.
One-click installer. The easiest option for players, and the one worth its own section below.
This is the one to use when the people you're sharing with aren't technical. Instead of a zip they have to install by hand, they get an installer they just run.
Tick Build one-click installer and you get a single file to share. Your friend extracts it and runs the exe, and it does the rest. It sets up the right Forge version, picks a sensible amount of RAM for their PC, and adds a profile for the pack to the official Minecraft launcher. When it's finished they open the launcher, pick the pack from the profile dropdown, and press Play.
When you tick it, you also choose how the pack is delivered. Self-contained packs the whole modpack inside the installer, so you send that one file and it needs nothing else. Hosted (cloud) uploads the pack to your MC Server Manager cloud storage and the installer only carries a link to it, which is what lets the pack update itself later (covered just below). Hosted needs cloud storage on your account, which comes free with Relay Pro, so if you don't have it the option stays hidden and you just use Self-contained.
Ticking the installer turns the separate client pack off, since the installer already bundles it in. If you want both, the installer for most people and a plain zip for anyone who'd rather not run an exe, just tick the client pack back on.
If they've installed the pack before, it asks whether to keep their current video settings and controls or reset them to the pack's defaults. Keeping is the default, so re-running it never wipes their tweaks.
A few things worth knowing:
Send each person the file that fits them, the installer or the client pack for players, the server pack for whoever's hosting.
How you update depends on which installer you built. A Self-contained installer has the pack baked in, so to push a new version you build it again and send the new file (re-running the old one just repairs that same version). A Hosted (cloud) installer is the easy one: the pack lives in your cloud storage at a fixed link, so when you rebuild the pack your players just run the same installer they already have and it pulls the new version automatically, with no resending files. That's the one to reach for if you change mods often.
No. The client pack, the server pack and the one-click installer are all standalone. The only thing the one-click installer relies on is the official Minecraft launcher, which most players already have.
Forge, Fabric, NeoForge and Quilt can all export client and server packs. The one-click installer is Forge only at the moment, with the others planned.
Yes, if you build a Hosted (cloud) installer. The pack lives in your cloud storage at a fixed link, so after you rebuild it your players just run the same installer again and it pulls the latest version, you don't resend anything. A Self-contained installer has the pack baked in, so for that one you rebuild and share the new file. Hosted needs cloud storage, which comes with Relay Pro.
Yes. Make a Modpack Project, drop your jars in or browse mods into it, and build from that. It's the same process, you just don't need a running server to start.
Make sure they've installed and opened the official Minecraft launcher at least once before running the installer. The installer adds a profile to it, so the launcher has to exist first. After that they should see the pack's profile in the dropdown.
A Modpacks folder on your Desktop by default. You can point the output somewhere else in the builder before you build.