Minecraft JAR Reverse Engineering

Core Rule

Prefer upstream source when available. Reverse engineer only what is necessary for the specific question.

Workflow

1. Hash the JAR.
2. Read manifest and mod metadata.
3. Extract:
   • mod ID;
   • version;
   • loader constraints;
   • Minecraft range;
   • dependencies.
4. Inspect mixin configs.
5. Map packages/classes relevant to the observed failure.
6. Decompile only targeted classes when needed.
7. Compare symbols/calls against dependency/API versions.
8. Search upstream source/release history for matching code.
9. Identify the smallest patchable incompatibility.
10. Rebuild only when toolchain and licensing/source conditions permit.
11. Re-test the original failure.

Watch For

• removed methods/classes;
• descriptor/signature changes;
• mappings mismatch;
• mixin targets moved;
• dependency range too strict/loose;
• metadata-only incompatibility;
• client-only references on server path.

Output

• JAR identity;
• relevant metadata;
• failing class/symbol;
• compatibility finding;
• patch feasibility;
• safest next step.