https://keras.io/api/layers/

Keras layers API

Layers are the basic building blocks of neural networks in Keras. A layer consists of a tensor-in tensor-out computation function (the layer's call method) and some state, held in TensorFlow variables (the layer's weights).

A Layer instance is callable, much like a function:

import keras
from keras import layers

layer = layers.Dense(32, activation='relu')
inputs = keras.random.uniform(shape=(10, 20))
outputs = layer(inputs)
# Unlike a function, though, layers maintain a state, updated when the layer receives data during training, and stored in layer.weights:

>>> layer.weights
[,
 ]
Creating custom layers

While Keras offers a wide range of built-in layers, they don't cover ever possible use case. Creating custom layers is very common, and very easy.

See the guide Making new layers and models via subclassing for an extensive overview, and refer to the documentation for the base Layer class.