Neural Sim is a free, browser-based neural network visualization built by MagicPill Labs. It lets you configure a network's layer count, layer width, and activation functions, then watch signals propagate through it in real time. Nothing is uploaded and no account is required — the simulation runs entirely in your browser.
Hover over the canvas to inject signals. Use the control panel to customize the network.
Go to AppWhat Neural Sim shows
A neural network is a stack of layers, each holding a set of nodes. A signal entering the network is multiplied by the weights on each connection, summed at every node, and passed through an activation function that decides how much of it continues forward. Neural Sim animates that path directly: you inject a signal, and you watch which nodes light up, how strongly, and how far the signal carries before it decays.
How to use it
- Set the number of layers and how many nodes each layer holds.
- Pick an activation function to change how signals decay or saturate between layers.
- Hover over the canvas to inject a signal at that point in the network.
- Adjust the colour scheme to make weak and strong activations easier to tell apart.
What it is not
Neural Sim does not train a model, load a dataset, or produce predictions. It is a tool for building intuition about network shape and signal flow — useful for teaching, for explaining an architecture to a non-technical stakeholder, or for anyone who has read about activation functions and wants to see one behave. For evaluating real models, MagicPill Labs builds SparkEval.
Who built it
Neural Sim is a free App Lab microapp from MagicPill Labs, an AI-native software development studio in Ridgefield, Washington. It runs entirely in the browser: nothing is uploaded, and no account is required. If you need a custom tool like this built for your own team, start with a free intro call.