Announcing EML 2.7: Custom loaders

We are releasing a major update to both EML AdminTool and EML Lib. This update brings native, automated support for custom version.json and assetIndex.json manifests, fundamentally improving how custom loaders and highly modified modpacks are distributed.

The challenge with custom manifests

When working with specific loaders (Forge, NeoForge, Fabric, Quilt) or experimental modpacks, administrators often need to modify the core game manifest. Previously, distributing a modified assetIndex or injecting custom libraries outside of standard Maven repositories was difficult. Any misconfiguration in the JSON structure or ID collisions could lead to missing textures, silent crashes, or 404 download errors.

What’s new in EML AdminTool

Open the Change loader modal. Start by selecting your desired base loader (the one you customized). Then toggle “Customize the selected version” and click Next. You can now upload your custom files.

The AdminTool backend has been heavily upgraded to parse, validate, and securely rewrite custom game manifests on the fly:

• Dynamic URL rewriting: Administrators can now upload a custom version.json. By setting target URLs to eml://upload, the EML AdminTool automatically replaces them with absolute, secure paths pointing to your server.
• Asset index synchronization: The system automatically processes custom assetIndex.json files. It recalculates the SHA-1 hash and file size, and silently synchronizes the assetIndex.id and assets properties. This prevents file collisions with Vanilla Minecraft installations in the player’s folder.
• Automated file routing: The system maps the uploaded custom libraries and correctly moves them to the appropriate endpoint directories.

Updates to EML Lib

To support these backend capabilities, EML Lib’s download and launch engine has been deeply updated:

• Single download process: When selecting a modded version (whether it’s a custom or a standard loader), EML Lib now downloads everything in a single pass, instead of separate passes for Vanilla and modded files.
• Smart URL detection: The library now intelligently distinguishes between standard Maven repository mirrors and direct file URLs, so that EML AdminTool can safely rewrite them to point to your server when using custom version.json files.

Ready to update?

Upgrading to v2.7.0 is simple:

1. Update the EML AdminTool via the settings page.

2. Update your launcher project by running npm i eml-lib@latest.

Read the docs for more information on how to use the new features.