Just download MCUpdater from mcupdater.com! To add modpacks, press the “+” in the top-left corner and insert the .XML modpack definition URL provided by the modpack creator. To update a modpack, press “Update”; keep in mind launching Minecraft does not automatically update the modpack.

• Publicly accessible HTTP web server,
• Familiarity with the terminal or command line, mostly! No GUIs here, sorry.

1. Prepare your modpack directory (config/, mods/, …)
2. Download MCU-FastPack-latest.jar
3. Run the following command:

   java -jar MCU-FastPack-latest.jar --path MODPACK_PATH --baseURL HTTP_WEB_SERVER_URL --mc MC_VERSION --out XML_FILE

   , where:

   • MODPACK_PATH is the location of the modpack files created in the first step,
   • HTTP_WEB_SERVER_URL is the upload location URL (for instance, http://example.com/modpack/),
   • MC_VERSION is the Minecraft version (for instance, 18w50a),
   • XML_FILE is the output XML filename. You will edit and upload this in later steps.
4. Visit https://fabricmc.net/use, select the desired Fabric loader versions and click “copy MCUpdater import url”.
5. Open the XML file in your favourite editor of choice and perform two changes (example provided below):
   1. Add the following entry below <Server…>: <Import url=“COPIED_URL”>fabric</Import>, where COPIED_URL is the MCUpdater import URL from the previous step,
   2. Add the following attribute to the <Server> element: mainClass=“net.fabricmc.loader.launch.knot.KnotClient”.
6. Upload the modpack files created in the first step as to make them visible beneath HTTP_WEB_SERVER_URL,
7. Upload the XML file to your HTTP web server URL - the location and filename does not matter other than for linking users. If you want to update the modpack later, just replace that XML file in the same location!

You're done! You now have an MCUpdater Fabric modpack.

A full guide is provided here.