Vivarium MCP server

Vivarium

A small world that evolves on its own.

Vivarium is a living terrarium in a web page. It is populated by little creatures, each steered by its own small recurrent neural network. Nobody tells them how to behave. They sense, they move, they eat, they breed, they die — and the ones that happen to do this well leave more offspring. Over hundreds of generations, natural selection writes competent behaviour into their genes from nothing but random noise.

There is no scripted AI here. Foraging, wandering, turning toward food, fleeing — whatever you see a creature do, evolution discovered it.

Open index.html in a browser and watch.

Run it

It's a single static page with zero dependencies and no build step.

• Easiest: double-click index.html (it runs straight from file://).
• Or serve it (nicer for some browsers):

python -m http.server

then open .

That's it. The simulation starts immediately.

What you're looking at

lineages spread across the world and slowly drift apart in colour.

• Creatures are little oriented swimmers.
• Their fill colour is a heritable hue — so you can literally see family

carnivore, amber an omnivore.

• Their rim runs green → red with diet: green is a herbivore, red a

and flashes red when they bite.

• Brightness tracks how well-fed they are; a snout points the way they face

cluster into patchy "meadows".

• Green dots are plants — the base of the food web. They grow over time and

age, generation, offspring) and a live diagram of its neural net, lit up as signals flow from senses → mind → muscles in real time.

• Click any creature to open the inspector: its genome (size, diet, vision,

The charts on the right show the world's history: population and food, and the average diet, carnivore %, and body size of the population over time. Watching those lines move is watching evolution happen.

The rules of the world

Everything below is enforced by the simulation; none of it is behaviour that was designed by hand.

Senses. Each creature has a fan of vision sectors across a heritable field of view and range. Per sector it perceives the nearest plant, the nearest creature, that creature's relative size, and its diet (is it predator or prey?). It also feels its own energy, speed, age, and an internal oscillator.

Mind. Those senses feed a fixed-topology recurrent neural network (the brain). The recurrence gives it short-term memory. Its three outputs are turn, thrust, and bite. The network's weights are genetic.

Body & metabolism. Size, diet, colour, and vision are genes too. Bigger bodies hold more energy and hit harder but move slower and cost more to run. Just existing burns energy; moving burns more. Run out and you die.

Eating. Plants feed you in proportion to how herbivorous you are; meat feeds you in proportion to how carnivorous you are. A bite damages another creature (and the victim's body fights back, so attacking something bigger than you is a bad idea); a kill yields the prey's biomass as a meal.

Reproduction. Asexual. Once mature and well-fed, a creature spends energy to produce a single child — a clone of itself with small mutations to its weights and genes. That is the only source of variation, and the engine of all change.

Death. Starvation, predation, or old age.

Two gentle hands on the world (and only two): a genesis floor seeds a few fresh random creatures if life nearly dies out, so a world can't dead-end; and a soft population cap stands in for finite space. Everything else is selection.

What evolves

Shortened. The full README is on GitHub.