b2KIT

Neural Network Visualizer

Build feedforward neural networks layer by layer. Train on simple datasets and watch weights, activations, and loss converge in real time.

Tested tool guide Tested browser tools Checked August 16, 2026

What Neural Network Visualizer does and how it behaves

Trace a feedforward network from its input layer through hidden units to its predictions while training changes the connections. You can assemble layers, run a simple dataset through them, and observe weights, unit activations, and loss as learning progresses. The display connects normally abstract quantities to the network's behavior: activations show the signals produced for particular inputs, while loss summarizes prediction error. The common surprise is that a falling training loss does not prove that the network discovered the intended rule or will predict unseen examples correctly.

How the result is produced

1

Forward computation

Each example moves through the layers in one direction, from input to output. A unit combines values arriving through weighted connections and applies its activation function to produce the value sent onward. The visualization exposes these intermediate activations and weights, allowing you to relate a prediction to particular paths through the network rather than seeing only the final output.

2

Learning by backpropagation

Training first compares the network's predictions with the dataset's targets to obtain a loss. Backpropagation determines how changes to individual weights would affect that loss, after which the weights are adjusted and another training step can run. Watching successive steps reveals whether loss is converging, oscillating, or barely changing, and whether hidden units are developing distinct activation patterns.

Good uses

  • Demonstrating to a class how hidden-layer activations and connection weights change during backpropagation.
  • Comparing shallow and deeper feedforward layouts on the same simple classification or regression dataset.
  • Investigating why a small network's loss stalls by watching inactive units, weakly changing weights, or unstable predictions.

Limits and checks

  • Loss is meaningful only together with the displayed dataset and the tool's chosen loss definition. Values from different tasks or loss functions are not directly comparable.
  • A visually converged training run can still memorize the examples. Without separate validation data, the display does not establish performance on unseen inputs.
  • Individual learned weights are not unique explanations. Different sets of weights can represent similar input-output behavior, especially when hidden units can exchange roles.

Common questions

Does reaching a very small loss mean the network found the correct model?

No. It means the current parameters fit the examples according to the loss being displayed. A network may fit a small dataset while behaving poorly between or beyond those examples. Treat the visualization as evidence about optimization and internal activity, not as proof of generalization, causality, or a uniquely correct network structure.

Why can adding more hidden units make the visualization harder to interpret?

Additional units create more activations and weighted connections, and several units may learn overlapping or interchangeable roles. The network may gain capacity while losing a simple visual explanation. More units also do not guarantee lower loss in every observed training interval, because successful training depends on how the parameters evolve, not only on how many parameters exist.

References and verification

The behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.

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