Flap

Flap is a javaagent allowing for pre-launch cross-intermediary remapping of mods.

Installation

Flap is currently shipped by the native Ornithe Installer by default. It is not included by the java-based installer as of 2026-03-14.

Supported Intermediaries

Flap supports the following intermediary variants out of the box:

• Official (Upstream Fabric)
• LegacyFabric (Version 1 & Version 2)
• Babric (Old Format & New Format)
• Ornithe (Version 1 & Version 2)
• Antiquity (obfuscated)

Configuration

Should Flap not detect a mod's variant correctly it is possible to override it.

Config File

Flap will read a config file at config/flap/mod_variants.json

Example:

{
  "modid": "ORNITHE_V2"
}

JVM Properties

Flap will also check system properties at flap.intermediary_variant_fallback.modid.

Example:

-Dflap.intermediary_variant_fallback.modid=ORNITHE_V2