modrinth.index.json — The Manifest Inside Every .mrpack

What it is

modrinth.index.json is a JSON file at the root of every .mrpack. It describes the modpack — which Minecraft version, which loader, and an exhaustive list of mods with download URLs and hashes.

Example

{
  "formatVersion": 1,
  "game": "minecraft",
  "versionId": "1.2.3",
  "name": "My Modpack",
  "files": [
    {
      "path": "mods/sodium.jar",
      "hashes": {
        "sha1": "...",
        "sha512": "..."
      },
      "downloads": [
        "https://cdn.modrinth.com/data/.../sodium-0.5.jar"
      ],
      "fileSize": 832544
    }
  ],
  "dependencies": {
    "minecraft": "1.20.1",
    "fabric-loader": "0.15.0"
  }
}

Key fields

formatVersion

Currently always 1. Reserved for future Modrinth spec changes.

game

Always "minecraft" today; reserved for other games Modrinth may host.

versionId / name

The author-defined version label and human-readable pack name.

files[]

The "shopping list." Each entry has a target path (where the file goes inside the instance), one or more downloads URLs, a fileSize, and hashes for integrity verification.

dependencies

Minimum Minecraft version and required mod loader version. The converter uses this to log which loader you must install in your target launcher.

Why two hashes (SHA-1 + SHA-512)?

SHA-1 is included for backward compatibility with older tools. SHA-512 is the canonical integrity check. Our converter uses SHA-512 to verify every download.