MDFM - Mod Downloader From Modrinth (Forge 1.20.1)

A mod that, before reaching the main menu, checks whether any "external" mods are missing from the mods/ folder and, if so, shows a mandatory screen asking for confirmation to download them from Modrinth.

Client-side only

This mod is client-only. It only acts inside FMLClientSetupEvent (which Forge never fires on a dedicated server) and every screen/GUI class it touches doesn't even exist in the dedicated server jar. The constructor also registers a DisplayTest extension point telling Forge's client/server handshake to ignore this mod's presence, so players won't see an "incompatible mod list" warning when joining a server that doesn't have it installed (including vanilla servers). You do not need to add this mod to your server's mods/ folder.

How to integrate it into your project

These files are meant to be copied into an existing Forge 1.20.1 project (MDK / ForgeGradle) that you already have set up, like the ones you usually work with:

1. Copy the src/main/java/com/danielhackerxd/modpackdownloader/ folder into your src/main/java/ (or adapt the package to your own convention, changing the package declaration in every class — this is independent of the mod id below).
2. Copy the contents of META-INF/mods.toml into your project's mods.toml, or merge it in if you already have other mods in the same jar (you can have several [[mods]] blocks in the same mods.toml). The mod id is mdfm.
3. Copy assets/mdfm/lang/ and pack.mcmeta into your src/main/resources/. If your project already has its own pack.mcmeta, don't overwrite it — just make sure its pack_format is 15 (or otherwise compatible with 1.20.1) and add the assets/mdfm/lang/ folder alongside your existing assets.
4. No extra dependencies are needed: it only uses Gson and java.net.http.HttpClient, which already ship with Minecraft/Forge.
5. Build with your usual gradlew build.

Usage flow

1. First launch after installing the mod (no mods.json yet): no warning is shown. Only config/mdfm/mods.json (a sample template) and config/mdfm/README.txt are generated.
2. You, as the pack author, edit mods.json with the real mods (see the format below) and distribute the modpack with that file already filled in.
3. On the end player's side: when the game opens, if any of the listed files is missing from mods/, the warning screen appears BEFORE the main menu, blocking the game (Esc does not close it).
   • All checkboxes start checked.
   • If the player unchecks one, the Next button becomes disabled (greyed out); trying to press it (or unchecking one after Next was already active) shows an explanation of why they can't continue.
   • Pressing Next with everything checked downloads the mods into mods/.
   • On success, the player is asked to restart the game (the new jars can't be hot-loaded; Forge only loads them on launch).
   • If any download fails, a warning is shown along with a Retry button. Downloads also automatically retry a few times with a short backoff if Modrinth responds with a rate limit (HTTP 429), before giving up.
4. Subsequent launches: as soon as every listed file already exists in mods/, the screen no longer appears.

Supported links (automatic resolution)

You don't need to manually dig up the direct CDN link: you can paste a normal Modrinth version page URL as-is, e.g. https://modrinth.com/mod/entityculling/version/MloBcsQQ. The mod calls Modrinth's public API (api.modrinth.com) to resolve it into the real CDN download link. No API key or account is needed — Modrinth's public API has no such requirement.

Any other link (one that's already a direct .jar link, e.g. cdn.modrinth.com/..., from your own server, etc) is used as-is, with no resolution.

If Modrinth changes the structure of their pages or their API in the future, this automatic resolution could stop working and the regular expression in ModDownloader.MODRINTH_VERSION_PAGE would need to be updated.

config/mdfm/mods.json format

[
  {
    "name": "Paraglider",
    "url": "https://modrinth.com/mod/paraglider/version/AbCdEfGh",
    "fileName": "paraglider-1.20.1.jar"
  },
  {
    "name": "Entity Culling",
    "url": "https://cdn.modrinth.com/data/XXXXXXXX/versions/YYYYYYYY/entityculling-forge-1.10.5-mc1.20.1.jar",
    "fileName": "entityculling-forge-1.10.5-mc1.20.1.jar"
  }
]

• url can be a normal Modrinth version page link, or an already-direct .jar link.
• fileName is the name it will be saved as inside mods/. It must match exactly so the "already installed" check works correctly on later launches.

Important notes

• This mod assumes the links are stable and publicly accessible. If Modrinth changes their download URLs over time, you'll need to update mods.json.
• There is no signature/checksum verification beyond confirming the downloaded file starts with a valid ZIP signature (PK\x03\x04), which only confirms it's a valid archive, not that it's the right one. If you want extra safety, an expected sha1/sha256 field could be added to mods.json and checked against the downloaded file's hash before moving it into mods/ — let me know if you'd like that added.
• The "already installed" check is based only on the file name in mods/. If the player deletes or renames the file, it will be asked for again.
• This version only supports Modrinth. CurseForge links are not recognized or resolved.

License & Use

All Rights Reserved