ApiExample.java

UpdatesFetcher.instance()
  .updateFor("modid") // returns an optional or maybe a future
  .ifPresent(update -> {
    System.out.println(update.url());
  });

fabric.mod.jsonc

{
  // ...
  "updates": "https://raw.githubusercontent.com/user/repo/master/modid.updates.json"
  // ...
}

modid.updates.json

{
  "schemaVersion": 1,
  "latest": {
    "release": "1.0.1",
    "snapshot": "1.1.0-pre1"
  },
  "versions": [
    {
      "id": "1.1.0-pre1",
      "type": "snapshot",
      "url": "https://github.com/user/repo/releases/tag/1.1.0-pre1"
    },
    {
      "id": "1.0.1",
      "type": "release",
      "url": "https://github.com/user/repo/releases/tag/1.0.1"
    },
    {
      "id": "1.0.0",
      "type": "release",
      "url": "https://github.com/user/repo/releases/tag/1.0.0"
    },
    {
      "id": "1.0.0-pre1",
      "type": "snapshot",
      "url": "https://github.com/user/repo/releases/tag/1.0.0-pre1"
    }
  ]
}