FAQ (Frequently Asked Questions)

This page contains answers to the most popular questions from the community.

How do I know if the ONNX model I have will run with Windows ML?

The easiest way to check if your model will run with Windows ML is by using the WinML Model Runner tool. Alternatively, you can check ONNX versions and Windows builds for more information on all supported ONNX versions for a given Windows release.

How do I convert a model of a different format to ONNX?

You can use WinMLTools to convert models of several different formats, such as Apple CoreML and scikit-learn, to ONNX.

I am getting errors when trying to export and/or convert my model to ONNX that say my model has "unsupported operators." What should I do?

Some operators in the native training framework might not be currently supported by an ONNX version. First, we recommend you check supported ONNX versions for your target Windows build, and try to convert your model to the max supported version. Later versions of ONNX include support for a larger set of operators compared to previous versions.

If you continue to run into issues, we recommend working with your data science team to try and avoid the unsupported operators. One of the approaches we recommend is to change the model's architecture in the source framework and attempt to convert/export the model to the target ONNX version. Note that you don't need to retrain the model yet—you can attempt to convert the architecture and, if successful, then you can move on to full retraining of your model.

Why can't I load a model?

There are several reasons why you might have trouble loading a model, but one of the most common ones when developing on UWP is due to file access restrictions. By default, UWP applications can only access certain parts of the file system, and require user permission or extra capabilities in order to access other locations. See File access permissions for more information.

Which version of WinMLTools should I use?

We always recommend you download and install the latest version of the winmltools package. This will ensure you can create ONNX models that target the latest versions of Windows.

Can I use onnxmltools instead of winmltools?

Yes, you can, but you will need to make sure you install the correct version of onnxmltools in order to target ONNX v1.2.2, which is the minimum ONNX version supported by Windows ML. If you are unsure of which version to install, we recommend installing the latest version of winmltools instead. This will ensure you will be able to target the ONNX version supported by Windows.

Which version of Visual Studio should I use in order to get automatic code generation (mlgen)?

The minimum recommended version of Visual Studio with support for mlgen is 15.8.7. In Windows 10, version 1903 and later, mlgen is no longer included in the SDK, so you'll need to download and install the extension. There is one for Visual Studio 2017 and one for Visual Studio 2019.

I get an error message when trying to run mlgen and no code is generated. What could possibly be happening?

The two most common errors when trying to execute mlgen are:

  • Required attribute 'consumed_inputs' is missing: If you run into this error message, then most likely you are trying to run an ONNX v1.2 model with a version of the Windows 10 SDK older than 17763; we recommend that you check your SDK version and update it to version 17763 or later.
  • Type Error: Type (map(string,tensor(float))) of output arg (loss) of node (ZipMap) does not match the expected type...: If you run into this error, then most likely your ONNX model is an older version than the one accepted by WinML starting with build 17763. We recommend that you update your converter package to the latest available version and reconvert your model to the 1.2 version of ONNX.

What does WinML run on by default?

If you don't specify a device to run on with LearningModelDeviceKind, or if you use LearningModelDeviceKind.Default, the system will decide which device will evaluate the model. This is usually the CPU. To make WinML run on the GPU, specify one of the following values when creating the LearningModelDevice:

  • LearningModelDeviceKind.DirectX
  • LearningModelDeviceKind.DirectXHighPerformance
  • LearningModelDeviceKind.DirectXMinPower


Use the following resources for help with Windows ML:

  • To ask or answer technical questions about Windows ML, please use the windows-machine-learning tag on Stack Overflow.
  • To report a bug, please file an issue on our GitHub.