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ATLauncher is a popular launcher and modpack platform with hundreds of community-created modpacks. Prism Launcher provides native support for browsing and installing ATLauncher modpacks directly.

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Overview

The ATLauncher integration offers:
  • Direct modpack access - Browse ATLauncher’s complete modpack catalog
  • Optional mod selection - Choose which optional mods to install
  • Public and semi-public packs - Support for both public and code-protected packs
  • Version selection - Install specific modpack versions
  • Share code support - Install packs using share codes
  • Automatic configuration - Handles complex installation rules and dependencies

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Creating an ATLauncher Instance

1

Open the New Instance dialog

Click Add Instance from the main window.
2

Navigate to ATLauncher

Select the ATLauncher tab in the new instance dialog.
3

Browse modpacks

The interface displays available ATLauncher modpacks. Use the search bar to filter by name.
4

Select a modpack

Click on a modpack to view its description and available versions.
5

Choose version

Select your preferred modpack version from the dropdown menu.
6

Configure optional mods (if applicable)

Some modpacks offer optional mods or configurations. A dialog will appear allowing you to customize your installation.
7

Create the instance

Click OK to download and install the modpack.

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Optional Mod Selection

Many ATLauncher modpacks include optional mods that you can choose to install or skip.

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Mod Types

ATLauncher supports various mod types with different installation behaviors:
  • Required mods - Automatically installed, cannot be disabled
  • Optional mods - User choice to install or skip
  • Recommended mods - Suggested by pack author, pre-selected but optional
  • Hidden mods - Only shown if dependencies are met
  • Library mods - Dependencies for other mods

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Mod Dependencies

Optional mods may depend on other mods. The launcher:
  1. Automatically enables required dependencies
  2. Warns if you disable a mod that others depend on
  3. Provides color-coded warnings for compatibility issues
Some mods may have conditional visibility based on other selections. The dialog updates dynamically as you make choices.

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Mod Installation Types

ATLauncher modpacks define specific installation rules for different file types:

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Standard Types

  • Root - Files placed in the instance root directory
  • Forge - Forge mod loader files
  • Jar - Files to be added to the Minecraft jar (legacy)
  • Mods - Standard mods folder
  • Coremods - Core mod directory

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Special Types

  • Resource Packs - Installed to resourcepacks folder
  • Shader Packs - Installed to shaderpacks folder
  • Texture Packs - Legacy texture packs (pre-1.6)
  • Plugins - Server plugins (for MCPC+ packs)

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Archive Types

  • Extract - Archives extracted to specified locations
  • Decomp - Decompressed files
  • Millenaire - Special handling for Millenaire mod
The launcher automatically handles file placement based on the pack’s manifest specifications.

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Share Codes

ATLauncher supports share codes for semi-public and private modpacks.
1

Get a share code

Obtain a share code from the modpack author or community.
2

Enter the code

In the ATLauncher tab, look for the share code input field.
3

Load the pack

Enter the code and the launcher will fetch the modpack information.
4

Install normally

Proceed with installation as you would for any modpack.
Share codes are unique to each pack and may expire. Contact the pack author if a code doesn’t work.

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Version Selection

ATLauncher modpacks often have multiple versions available:

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Version Types

  • Recommended - Pack author’s recommended version
  • Latest - Most recent release
  • Older builds - Previous versions for compatibility or preference
Each version specifies:
  • Compatible Minecraft version
  • Required mod loader version
  • Included mods and their versions

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Technical Details

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Pack Manifest Structure

ATLauncher modpacks use detailed JSON manifests that define: 
{
  "version": "1.0.0",
  "minecraft": "1.20.1",
  "loader": {
    "type": "forge",
    "version": "47.2.0",
    "latest": false,
    "recommended": true
  },
  "mods": [
    {
      "name": "Example Mod",
      "version": "1.0",
      "type": "mods",
      "url": "https://...",
      "md5": "abc123",
      "optional": false,
      "recommended": true,
      "download": "direct"
    }
  ]
}

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Download Types

ATLauncher supports multiple download methods:
  • Direct - Direct download from URL
  • Server - Download from ATLauncher’s servers
  • Browser - Requires manual browser download (rare)

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File Verification

All downloaded files are verified using MD5 checksums to ensure integrity.
If a file fails verification, the launcher will automatically retry the download.

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Configuration Files

ATLauncher modpacks can include custom configuration files:
  • Configs - Mod configuration files with specific settings
  • Keeps - Files to preserve during updates
  • Deletes - Files to remove during installation

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Update Behavior

When updating an ATLauncher pack:
  1. Files marked as “keep” are preserved
  2. Files marked for deletion are removed
  3. New configurations are applied
  4. Optional mods selection is re-prompted if changed

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Sorting Options

The ATLauncher browser provides several sorting methods:
  • Position - Pack author’s preferred ordering
  • Name - Alphabetical
  • Type - Public vs. semi-public packs

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Color-Coded Warnings

The optional mod dialog uses colors to indicate:
  • Red warnings - Critical issues or incompatibilities
  • Yellow warnings - Cautions or performance notes
  • Standard - No warnings
Pay attention to colored warnings when selecting optional mods. They often indicate known issues or conflicts.

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Troubleshooting

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Common Issues

“Failed to load modpack list”
  • Check your internet connection
  • Verify ATLauncher’s API is accessible
  • Try refreshing the page
“Download failed for mod”
  • Some mods may have temporary hosting issues
  • Check if the mod requires manual download
  • Try again later or contact pack author
“Optional mods not showing”
  • Ensure dependencies are selected first
  • Some mods are hidden until requirements are met
  • Check for updates to the modpack
“Share code invalid”
  • Verify the code was entered correctly
  • Check if the code has expired
  • Contact the pack author for a new code

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Custom Main Classes

Some ATLauncher packs specify custom main classes:
The launcher automatically handles custom main classes and extra JVM arguments specified by the pack manifest.

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Source Code Reference

The ATLauncher integration is implemented in:
  • /launcher/modplatform/atlauncher/ATLPackIndex.h - Pack metadata
  • /launcher/modplatform/atlauncher/ATLPackManifest.h - Manifest structures
  • /launcher/modplatform/atlauncher/ATLPackInstallTask.cpp - Installation logic
  • /launcher/modplatform/atlauncher/ATLShareCode.h - Share code handling
  • /launcher/ui/pages/modplatform/atlauncher/AtlPage.cpp - User interface