Tailcat for Minecraft

Tailscale published Tailcat for Minecraft, an unofficial, mostly AI-generated Fabric 1.21.1 client mod prototype that shares an integrated Minecraft world over Tailcat's userspace WireGuard, magicsock direct NAT traversal and DERP fallback without a TUN interface or a Tailscale installation. The mod splits responsibilities so Java owns Minecraft UI and process lifecycle while a bundled Go helper handles all networking and encryption, and it restricts sharing to virtual TCP port 25565 with join listeners bound only to 127.0.0.1 and capped concurrent streams. Tailscale states it is not an officially supported product and that the company has no plans to distribute it; the repository is provided for demonstration and amusement only.

Warning This is a quick, mostly AI-generated prototype demonstrating one way to use Tailcat. It is not an officially supported Tailscale product, and Tailscale has no plans to distribute it. This repository is provided for demonstration and amusement only. A Fabric 1.21.1 client mod that shares an integrated Minecraft world through Tailcat https://github.com/tailscale/tailcat 's standard userspace WireGuard, magicsock direct NAT traversal, and DERP fallback. It creates no TUN interface and requires no Tailscale installation. Java owns Minecraft UI/process lifecycle; the bundled Go helper owns all networking and encryption. tailcatmcdemo.mp4 Requirements are JDK 21, curl , and tar . The helper uses the public Tailcat Go module https://github.com/tailscale/tailcat . The native build script downloads the required Tailscale Go toolchain: scripts/build-natives.sh ./gradlew :mod:build The normal JAR is written to mod/build/libs/ . For Java-only development, set MCLINK HELPER to a locally built helper path. The native build produces and checksums Windows, macOS Intel and Apple Silicon , and Linux helpers. The host pauses a single-player game and clicks Share with Tailcat , then copies the mcl1 ... invitation. The other player opens Multiplayer, clicks Connect with Tailcat , pastes it, and connects. Opening remote sharing publishes the integrated server using Minecraft's normal LAN behavior if it is not already published. The versioned invitation wraps an ephemeral Tailcat connection token. Possession of that unguessable token authorizes access for the lifetime of the sharing session. The helper allows only virtual TCP port 25565, binds join listeners only to 127.0.0.1 , and caps concurrent streams. To test with one Minecraft account, launch only the host with the explicitly development-only offline-auth switch: MCLINK DEV OFFLINE AUTH=1 ./gradlew :mod:runClient Launch the second client from another terminal with an isolated game directory and a different offline username: mkdir -p mod/run-client2 ./gradlew :mod:runClient --args='--gameDir ../run-client2 --username Client2' The switch is ignored outside Fabric's development environment and the server's original online-mode setting is restored when Tailcat sharing stops. Never use this bypass for real remote sharing. The build is unsigned by default. Public release artifacts must Authenticode- sign both Windows executables, sign/notarize the two macOS executables, replace the packaged files, regenerate checksums.json , generate complete third-party notices, and then build the final JAR. Test separate machines and direct/DERP paths as listed in the project brief. Generate the dependency notices from the locked Go module graph for example, with go-licenses report ./... . Tailcat and Tailscale are BSD-3-Clause licensed; Fabric Loader/API are runtime dependencies rather than embedded mod contents, and Minecraft remains subject to Mojang's terms.