Browsercraft: Java Minecraft in the browser

Original Article ↗ Hacker News Discussion ↗

Return of Java in the Browser / Applet Nostalgia

  • Many note the “full circle” feel: Minecraft originally shipped as a Java applet, and now Java Minecraft is back in the browser, though via WASM instead of plugins.
  • Some argue it’s not truly “full circle” because this uses built‑in browser capabilities instead of a sideloaded runtime/extension.
  • Several reminisce about Java applets: both frustration (slow, clunky reputation) and praise (fast enough when written carefully and kept lean).

Security: JVM vs Browser/WASM Sandboxes

  • Commenters recall the original JVM SecurityManager and permission model; some think the sandbox was conceptually solid but too complex, others recall it being easy to bypass.
  • WASM’s sandbox is seen as a security improvement, though people caution that adding rich APIs (e.g., codecs) tends to erode sandbox guarantees over time.

Legality and Piracy Debate

  • Strong disagreement over whether this is “playing Minecraft for free” illegally or just running a publicly available legacy client.
  • One side: overall effect is offering paid content for free, arguably violating EULA/DMCA by bypassing account checks.
  • Other side: the JAR is hosted by Mojang, linked from the official wiki, and run unmodified; no authentication is circumvented, so claims of “prison time” are dismissed as FUD.
  • Whether any “free trial” or access control is being misused is described as unclear.

Performance and Browser Tech

  • Reports of ~20 FPS even on strong hardware lead some to call this evidence of browser regression and heavy layering (Java → WASM/WebGL → GPU).
  • Others note vanilla Minecraft itself performs poorly natively, often needing performance mods; recent native versions have fixed long‑standing FPS bugs.
  • Suggestions include moving the JVM to a Web Worker and better exploiting WASM features; some complain WASM’s memory model still blocks near‑native performance.

CheerpJ Technology & Roadmap

  • The demo runs the unmodified Minecraft JAR on CheerpJ, a WebAssembly-based JVM supporting Java 8/11, with Java 17 planned.
  • JavaFX isn’t supported yet due to its heavy native C++ use; similar techniques to those used for LWJGL are planned.
  • Small-business self‑hosting licenses are slated for CheerpJ 4.0 (mid‑2025).

Comparisons and Alternatives

  • Eaglercraft is highlighted as a more advanced browser Minecraft (up to 1.8.9, with multiplayer), built via TeaVM (Java→JS/WASM).
  • Some dream of fully modded, sandboxed Minecraft in the browser to revive the “golden age” of Java modding without install friction.

Mobile, UX, and Miscellany

  • Demo runs on phones, but performance and especially input (“mouse look” vs touch) are still problematic; better mobile UX is a stated future goal.
  • Various anecdotes underscore Minecraft’s longevity across generations, library and school-firewall nostalgia, and kids turning the game into chaotic combat or destruction.