Valheim Sim — scout Valheim seeds and test builds in the browser | Mohammad Mahdi Afshar

What it is

Valheim Sim is a browser-based prototype of Valheim's hammer-mode building. You type a world seed, fly over the generated terrain, and build with snapping floors, walls, beams, poles and roofs while a structural-integrity model tells you whether the build would actually stand in the game.

World generation

The world generator is a port of the game's own algorithm, based on the decompiled code documented by kirilloid/valheim: Unity's Mathf.PerlinNoise, UnityEngine.Random (xorshift128), the world generator with rivers and streams, and the zone system's location placement. The project README states that a seed produces the same landmasses, biomes, boss altars, traders and spawn as the current game version, with coordinates matching the game's debug coordinates, and lists its caveats:

major-location placement models only the nine major location types (bosses, traders, spawn), so one can very rarely land one 64 m zone away from where the game would put it;
64-bit floats (the game uses 32-bit) can flip single pixels on biome borders;
minor location types use a lower iteration cap than the game, so the list is an exact prefix of the game's and may miss a few tail instances.

Press M for the world map: bosses, traders, dungeons, settlements and points of interest, grouped, searchable and filterable. Click anywhere to fly there.

Structural integrity

Pieces touching terrain are grounded. Every other piece's stability is its breadth-first distance through touching pieces to the ground, coloured from green to red. Wood supports at most five steps; placement beyond that is refused. Delete a support and everything that loses its path to the ground breaks and falls. Undo and redo are cascade-safe.

Performance

Terrain streams in chunks — a 3×3 grid of detailed 200 m chunks around you with an LRU cache, plus a coarse far-field ring for the horizon. World placement and map rendering run in a Web Worker, trees are instanced, and idle frames skip rendering entirely.

Controls

Left click places (hold to repeat), right click deletes, right-drag orbits, R rotates, 1–5 pick a piece, WASD + QE move, M opens the map, H shows help.

Stack

TypeScript, React, three.js and Vite, deployed as a Cloudflare Worker serving static assets.

Fan-made and unofficial; not affiliated with the developers of Valheim.