Run trained Keras models in the browser, with GPU support


Run trained Keras models in your browser, GPU-powered using WebGL. Models are serialized directly from the Keras JSON-format configuration file and associated HDF5 weights.

Interactive Demos

  • Basic Convnet for MNIST

  • Convolutional Variational Autoencoder, trained on MNIST

  • 50-layer Residual Network, trained on ImageNet

  • Inception V3, trained on ImageNet

  • Bidirectional LSTM for IMDB sentiment classification


  • Eliminate need for backend infrastructure or API calls

  • Offload computation entirely to client browsers

  • Interactive apps


See demos/src/ for source code of real examples.

  1. Works for both Model and Sequential:
  model = Sequential()
  model = Model(input=..., output=...)

Once trained, save the weights and export model architecture config:

  with open('model.json', 'w') as f:

See jupyter notebooks of demos for details: demos/notebooks/.

  1. Run the encoder script on the HDF5 weights file:
  $ python /path/to/model.hdf5

This will produce 2 files in the same folder as the HDF5 weights: model_weights.buf and model_metadata.json.

  1. The 3 files required for Keras.js are:

    • the model file: model.json

    • the weights file: model_weights.buf

    • the weights metadata file: model_metadata.json

  2. GPU support is powered by weblas. Include the Keras.js and Weblas libraries:

  <script src="lib/weblas.js"></script>
  <script src="dist/keras.js"></script>
  1. Create new model

On instantiation, data is loaded over XHR (same-domain or CORS required), and layers are initialized as directed acyclic graph. Class method ready() returns a Promise which resolves when these steps are complete. Then, use perdict() to run data through the model, which also returns a Promise.

  const model = new KerasJS.Model({
    filepaths: {
      model: 'url/path/to/model.json',
      weights: 'url/path/to/model_weights.buf',
      metadata: 'url/path/to/model_metadata.json'
    gpu: true

  model.ready().then(() => {

    // input data object keyed by names of the input layers
    // or `input` for Sequential models
    // values are the flattened Float32Array data
    // (input tensor shapes are specified in the model config)
    const inputData = {
      'input_1': new Float32Array(data)

    // make predictions
    // outputData is an object keyed by names of the output layers
    // or `output` for Sequential models
    model.predict(inputData).then(outputData => {
      // e.g.,
      // outputData['fc1000']

Available layers

  • advanced activations: LeakyReLU, PReLU, ELU, ParametricSoftplus, ThresholdedReLU, SReLU

  • convolutional: Convolution1D, Convolution2D, AtrousConvolution2D, SeparableConvolution2D, Deconvolution2D, Convolution3D, UpSampling1D, UpSampling2D, UpSampling3D, ZeroPadding1D, ZeroPadding2D, ZeroPadding3D

  • core: Dense, Activation, Dropout, SpatialDropout2D, SpatialDropout3D, Flatten, Reshape, Permute, RepeatVector, Merge, Highway, MaxoutDense

  • embeddings: Embedding

  • normalization: BatchNormalization

  • pooling: MaxPooling1D, MaxPooling2D, MaxPooling3D, AveragePooling1D, AveragePooling2D, AveragePooling3D, GlobalMaxPooling1D, GlobalAveragePooling1D, GlobalMaxPooling2D, GlobalAveragePooling2D

  • recurrent: SimpleRNN, LSTM, GRU

  • wrappers: Bidirectional, TimeDistributed

Layers not yet implemented

Lambda cannot be implemented directly at this point, but will eventually create a mechanism for defining computational logic through JavaScript.

  • core: Lambda

  • convolutional: Cropping1D, Cropping2D, Cropping3D

  • locally-connected: LocallyConnected1D, LocallyConnected2D

  • noise: GaussianNoise, GaussianDropout


WebWorkers and their limitations

Kera.js can be run in a WebWorker separate from the main thread. Because Keras.js performs a lot of synchronous computations, this can prevent the UI from being affected. However, one of the biggest limitations of WebWorkers is the lack of <canvas> (and thus WebGL) access. So the benefits gained by running Keras.js in a separate thread are offset by the necessity of running it in CPU-mode only. In other words, one can run Keras.js in GPU mode only on the main thread.


In GPU mode, tensor objects are encoded as WebGL textures prior to computations. The size of these tensors are limited by gl.getParameter(gl.MAX_TEXTURE_SIZE), which differs by hardware/platform. See here for typical expected values. The may be an issue in convolution layers after im2col. For example, in the Inception V3 network demo, im2col in the 1st convolutional layer creates a 22201 x 27 matrix, and 21609 x 288 matrices in the 2nd and 3rd convolutional layers. The size along the first dimension exceeds most MAX_TEXTURE_SIZE, 16384, and therefore must be split. Matrix mutiplications are performed with the weights for each split tensor and then combined. In this case, a weblasTensorsSplit property is available on the Tensor object when createWeblasTensor() is called (see src/Tensor.js). See src/layers/convolutional/Convolution2D.js for an example of its usage.

Development / Testing

There are extensive tests for each implemented layer. See notebooks/ for jupyter notebooks generating the data for all these tests.

$ npm install

To run all tests run npm run server and simply go to http://localhost:3000/test/. All tests will automatically run. Open up your browser devtools for additional test data info.

For development, run:

$ npm run watch

Editing of any file in src/ will trigger webpack to update dist/keras.js.

To create a production UMD webpack build, output to dist/keras.js, run:

$ npm run build



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