FAQ
Is Retromod safe?
Retromod is open source, runs inside Minecraft, and is offline by default. Runtime transforms stay inside the selected game directory, and original mod jars are kept in retromod-input/processed/, mods/retromod-backups/, or the game-directory retromod-backups/ health-recovery folder. The standalone CLI can also read and write paths you explicitly give it.
It does rewrite third-party bytecode. Use mods from sources you trust, back up important worlds yourself, and test save-affecting mods in a copied instance first. Retromod’s jar backup is not a world backup and it does not sandbox a mod after launch.
Does it need internet access?
No. Normal transformation, caching, and verification are local. The native-version lookup is off by default and only queries Modrinth after check_for_native_versions or -Dretromod.checkForNativeVersions=true opts in. CLI archive download and archive preload use loader Maven repositories only after a prompt, unless you explicitly pass --yes.
Which versions work?
Retromod runs on Minecraft 1.20 through 26.2. Source support depends on the loader:
- Fabric: 1.14.4+
- Quilt: 1.18.2+
- NeoForge: 1.20.1+
- Forge: 1.12.2+
Coverage before 1.16.5 is experimental.
These are source-version floors, not host artifacts. Published host jars cover Fabric, Quilt, and Forge 1.20 through 26.2, plus NeoForge 1.20.1 through 26.2. Quilt uses the shared Fabric artifact.
Pre-26.1 Fabric hosts use targeted intermediary bridges instead of the full intermediary-to-Mojang remap. Common old text, entity, material, identifier, model, and entity-type migrations are covered, but redesigned APIs can still require a manual port.
Does it work on servers?
Yes. Install Retromod on every side that loads transformed code. Clients do not need it for a genuinely server-only mod.
Paper, Spigot, Bukkit, and Purpur plugins are not supported. Retromod targets Fabric, Quilt, NeoForge, and Forge mods.
Does it work with modpacks?
Yes. Keep old Fabric and Quilt mods in retromod-input/ so Retromod can process them before the loader’s version check. For repeatable distribution, prepare the pack with the CLI.
What happens to dependencies?
Retromod relaxes stale version ranges when it knows the dependency can be bridged. It does not invent a missing library. Install required dependencies unless Retromod provides a documented polyfill.
Can I run an old Forge mod on NeoForge?
Sometimes. Retromod bridges selected common 1.20.1 Forge metadata, registration, event-bus, networking, and removed-class paths. It is not a complete Forge runtime. Mods with deep registry lifecycle, packet delivery, data generation, rendering, or other Forge internals are still safer on a matching Forge host.
Can Retromod repair Mixins automatically?
For a narrow, proven subset. At game launch Retromod indexes the installed Minecraft classes. The CLI gets the same target facts from --mc-jar <target.jar>. It can repair unique parameter-addition changes, selected zero-capture or exact-prefix handlers, and MixinExtras value modifiers that capture every old target argument. It can also move a one-target, accessor-only Mixin when every accessor has an exact owner-scoped redirect to the same destination field.
It refuses mixed-purpose Mixins, unmatched companion accessors, ambiguous overloads or owners, constructors, conflicting field moves, descriptor changes, partial captures, reordered or removed parameters, return-type changes, semantic local captures, and unsafe annotations. A moved setter receives @Mutable only when its shim explicitly marks that exact destination.
The accessor owner move accepts remap = false only because an exact shim redirect proves both owners. Other automatic signature repairs refuse every relevant remap = false scope.
Curated adapters cover a few semantic migrations. Other save, worldgen, renderer, or networking changes still need a real bridge and feature testing.
Should Minecraft 26.2 use OpenGL or Vulkan?
Use OpenGL for translated mods. Old rendering code often assumes OpenGL, while Vulkan is the new default. Retromod selects OpenGL automatically unless you already chose a backend.
Does it work with OptiFine, Sodium, Iris, or Create?
Simple integrations may work, but renderer replacements and deep coremods are the hardest category and often cannot be translated. Check Mods That Can’t Be Translated and the compatibility database.
What does a modified-build warning mean?
The running classes do not match the embedded release hash. That can be a legitimate local build or fork. Compare the jar’s SHA-256 with the value on the official download page if the change was unexpected. See Authenticity.
Where are my files written?
Runtime inputs and originals use retromod-input/, retromod-input/processed/, mods/retromod-backups/, and the game-directory retromod-backups/ health-recovery folder. Staged resource packs use retromod-input/resourcepacks/, then successful output moves to resourcepacks/. Staged data packs use retromod-input/datapacks/, with successful output in retromod-output/datapacks/ for you to copy into a world. Successful pack sources move into the matching input folder’s processed/ subfolder.
Generated reports use config/retromod/verify-reports/. The normal AOT cache is config/retromod/aot-cache/. Full AOT state uses retromod-cache/full-aot/. API archives use config/retromod/api-archive/. CLI transform output defaults to a sibling jar, batch uses an input-folder retromod-output/, and aot uses the normal AOT cache unless you choose --output. The CLI initializes the standard input and backup folders in its current working directory.
Can I use Retromod commercially?
Yes. Retromod uses the MIT license. You still need to follow the licenses of Minecraft, the loader, and every mod in your pack.
Can I contribute?
Yes. Mapping fixes and focused redirects are good first changes. See Contributing.