Windows Compatibility

This page currently documents Windows (Windows 11 AMD64) only. Real-machine compatibility testing for macOS and Linux has not started yet and is omitted until verified.

Loader × Minecraft Version Matrix (Windows)

The matrix below summarizes real-machine compatibility across Minecraft version ranges and the five built-in runtime environments on Windows 11:

Verified Version Highlights

• Vanilla: End-to-end verified on 1.21.11, with isolated legacy asset paths ready for historical releases (1.6.4–1.12.2).
• Fabric: Verified on 1.16.5 (0.18.5, Java 8 direct -cp), 1.20.1 (0.15.10), 1.21.1 (0.16.7), 26.3 (0.19.5), and 26.4-snapshot-8 (0.20.1).
• Quilt: Verified on 1.20.1 (0.26.0), 1.21.1 (0.29.2, bundled mixinextras handled), 26.1 (0.30.0-beta.7), and 26.3 (0.30.2); 1.14 – 1.16.5 shares the Java 8 -cp fix.
• Forge: Verified across 1.6.4 (standalone 9.11.1.1345), 1.7.10, 1.8.9 (11.15.1.1902), 1.12.2 (14.23.5.2859), 1.16.5 (36.2.42), 1.18.2 (40.2.21), 1.20.1 (47.4.29), 1.21.1 (52.1.10), 1.21.5 (55.1.0), 26.1 (62.0.9), and 26.3 (66.1.8).

Automatic Java & Mirror Fallback Behavior

Under Settings → Download, the default download source is Auto (SourceAuto), combining official endpoints with safe mirror fallback while keeping strict integrity checks intact:

• Automatic Java installation (Windows): Tested end-to-end on Windows 11 for Eclipse Temurin 8 / 17 / 21 / 25 (including TUNA mirror fallback with SHA-256 verification) and Azul Zulu 8 / 17 / 21 (automatic fallback with 100-byte catalog size-rounding tolerance and full SHA-256 verification).
• Fixed-artifact & catalog mirrors: Supports BMCLAPI (for Forge, NeoForge, Fabric, and Minecraft version catalogs and /maven artifacts), Fabric-meta mirror fallback, and Aliyun Maven Central for immutable binary artifacts, with fast failover when an alternate candidate is available and no user rate limit is set.
• Strict verification policy: mcl never trusts .sha1 sidecar files from unofficial mirrors and never self-hashes unverified bytes. For legacy Forge (1.8.9), when official maven.minecraftforge.net .sha1 lookups time out, mcl only falls back to SHA-1-verified installer checksums or to official repo.maven.apache.org/maven2/ .sha1 metadata for non-Forge Maven Central dependencies.

Known Boundaries & Notes

NeoForge in networks without direct access to maven.neoforged.net

• With mirror fallback enabled, NeoForge (1.20.1, 1.20.4, 26.1, 26.3) version listing and modpack file downloads succeed.
• However, resolving NeoForge installer checksums and unpinned library metadata still requires reaching official .sha1 sidecars on maven.neoforged.net. On restricted networks without a proxy (where public mirrors do not serve trusted .sha1 sidecars), mcl refuses to bypass digest verification and reports a loader connectivity error. Install NeoForge over a direct connection or working proxy.

Legacy version & mod quirks observed on Windows

• Third-party Forge 1.6.4 modpacks: Standalone Forge 1.6.4 (9.11.1.1345) installs and opens a visible game window cleanly, whereas certain 2013 modpacks contain legacy mods (such as old CodeChickenCorePlugin) that crash during startup trying to fetch defunct remote libraries.
• Forge 1.12.2 with fullscreen:true: Some 1.12.2 packs shipped with fullscreen:true in options.txt may exit on an unattended first startup during menu initialization and launch cleanly on retry.

Explicitly Unsupported Scope

• Unsupported community loaders: Only Vanilla, Fabric, Quilt, Forge, and NeoForge are supported; legacy or unbundled loaders such as Legacy-Fabric, Babric, Ornithe, and LiteLoader are outside scope.
• Non-allowlisted download hosts: External archive links outside the allowlisted official repositories are rejected.
• Agents & third-party authentication: -javaagent: flags, skin/cape patching agents, authlib-injector, and third-party auth providers are explicitly rejected.