Import & Export

Last updated on

Supported Formats

Polymerium supports four modpack formats for both import and export:

Importing a Modpack

1. Click the + button to create a new instance.

2. Choose Import from file.

3. Select the modpack archive.

4. Polymerium auto-detects the format and imports:

   • The metadata is parsed and written to your instance's profile.json.
   • Pack files (configs, resources) are extracted to import/.
   • Online package references are resolved when the instance is deployed; offline pack files are read from the archive.

5. Deploy and play.

Updating a modpack? If the instance was created from an import, you can re-import a newer version of the same pack. Polymerium replaces import/ with the new files while leaving persist/ untouched — files you've moved there are preserved.

How Imported Packages Are Grouped

Packages associated with an online modpack form a modpack group on the Setup page. That group participates in the same priority and override mechanism as recipe groups and collections. A local CurseForge or Modrinth archive without an online source association instead places its package references in a collection named after the modpack; Trident imports can retain groups carried in the archive.

You can keep the modpack's package entries while adding overlapping projects through other groups or as loose packages. See Package Groups & Override Order for which entry is deployed. Configuration files supplied in Pack Source (import/) follow the separate directory layering rules.

Exporting an Instance

1. Select an instance.
2. Open the instance menu and choose Export.
3. Choose Trident or an external format, then review the format-specific options and pack metadata.
4. Review source association, offline mode, and excluded tags where available, then save the modpack archive. Pack Source files are included in the export.

What Gets Exported

Format-Specific Notes

• Trident Portable Instance (TPI) is Polymerium's native modpack format. Online exports retain package grouping, tags, deployment rules, selected instance overrides, imported native patches, and attachments. It does not carry the whole instance.
• CurseForge / Modrinth formats are widely compatible but lose Polymerium-specific features like tags and rules.
• MultiMC format is the most basic — just the mod list and configs. Instances imported as folders keep their local component definitions: those become native patches, which is how GTNH and Cleanroom instances keep a working launch plan.

Online vs. Offline Formats

Not all modpack formats work the same way under the hood:

• CurseForge and Modrinth formats are online — they contain references (package URLs) to mods hosted on those platforms, not the actual mod files. When you import one, the launcher resolves those references and downloads the mods.

  This means a CurseForge modpack should ideally only reference CurseForge mods, and a Modrinth modpack should only reference Modrinth mods. If you mix sources, the modpack won't pass platform review when publishing.

• MultiMC exports bundle files for offline use. Files supplied by a pack still need a suitable Minecraft version and loader when the instance is deployed.

• TPI is neither purely online nor offline. By default it stores online references (Prefs) and resolves mods at deploy time, but can optionally bundle mod files in offline mode. See the Trident Portable Instance section below for details.

Keep this in mind when choosing a format for publishing your modpack.

Trident Portable Instance

Trident Portable Instance (TPI) is Polymerium's own modpack format. Online exports retain more of the profile's package and deployment metadata than external formats, alongside the Pack Source files. It is not a snapshot or a full backup of the instance: Local Data (persist/), the Run Directory (build/), user patches, and account credentials do not travel with the pack.

What's Inside

A TPI .zip archive contains the index and options files, plus optional content when present:

Rich Metadata

In online mode, TPI preserves declarations that external formats cannot represent:

• Per-mod enable/disable state — not just which mods are included, but which are active
• Tags — user-defined labels for categorization
• Deployment rules — per-mod overrides for destination path, skipping, or normalization
• Instance overrides — JVM arguments, window size, server address, deploy strategy
• Package groups and order — collections and their saved order travel with online exports; local recipe groups become collections. If source information is excluded, online modpack groups also become collections instead of losing their grouping.
• Native patches — the imported patch layer travels with its assets, disabled entries and order; user patches stay local and never travel

TPI preserves these modpack declarations, not the complete local instance or its personal data.

Online by Default, Offline When Needed

TPI is a hybrid format:

• Online mode (default): Packages remain Pref references (for example, pref://modrinth/aC3cM3Vq@9I21YYxf). Deployment resolves and downloads their files. The source information option controls whether the original online modpack association travels; it does not remove Pack Source files.
• Offline mode (optional): Bundles the enabled packages' resolved files into the archive and removes their package references from the exported profile. It is not a backup of Local Data or every file in the Run Directory.

Online mode keeps archives smaller and leaves package download to deployment. The trident.index.json remains human-readable in either mode.

Instance Attachments

TPI can include instance-level attachments. If present in the instance home, the icon, README.md, CHANGELOG.md, and LICENSE.txt are exported (the license appears as LICENSE in the archive). These describe the instance itself rather than the game and remain separate from Pack Source files.

Ideal as Instance Templates

You can use TPI as a modpack template: import its profile declarations and included Pack Source files to create another instance. Check its Java runtime, account, and any local data separately before playing.

Recipes: Reference-Only Lists

Alongside the modpack formats above, Polymerium has a lightweight, reference-only format: recipes. A recipe is a named list of package references with optional tags and notes — no files, no configuration, and no Minecraft version or loader. Use it to share a curated mod selection and apply it when setting up an instance. See Recipes →.

Migrating From Another Launcher

If you're coming from another launcher, check the migration guide:

• Migrate from Other Launchers →