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Open Neural Network Exchange (ONNX) is an open ecosystem that empowers AI developers to choose the right tools as their project evolves. ONNX provides an open source format for AI models, both deep learning and traditional ML. It defines an extensible computation graph model, as well as definitions of built-in operators and standard data types. Currently we focus on the capabilities needed for inferencing (scoring).

ONNX is widely supported and can be found in many frameworks, tools, and hardware. Enabling interoperability between different frameworks and streamlining the path from research to production helps increase the speed of innovation in the AI community. We invite the community to join us and further evolve ONNX.


Learn about the ONNX spec

Programming utilities for working with ONNX Graphs


ONNX is a community project. We encourage you to join the effort and contribute feedback, ideas, and code. You can participate in the SIGs and Working Groups to shape the future of ONNX.

Check out our contribution guide to get started.

If you think some operator should be added to ONNX specification, please read this document.


We encourage you to open Issues, or use Slack for more real-time discussion

Follow Us

Stay up to date with the latest ONNX news. [Facebook] [Twitter]



A binary build of ONNX is available from Conda, in conda-forge:

conda install -c conda-forge onnx


If you have installed onnx on your machine, please

pip uninstall onnx
first before the following process of build from source.

Linux and MacOS

You will need an install of Protobuf and NumPy to build ONNX. One easy way to get these dependencies is via Anaconda:

# Use conda-forge protobuf, as default doesn't come with protoc
conda install -c conda-forge protobuf numpy

You can then install ONNX from PyPi (Note: Set environment variable

for onnx-ml):
pip install onnx

Alternatively, you can also build and install ONNX locally from source code:

git clone
cd onnx
git submodule update --init --recursive
python install

Note: When installing in a non-Anaconda environment, make sure to install the Protobuf compiler before running the pip installation of onnx. For example, on Ubuntu:

sudo apt-get install protobuf-compiler libprotoc-dev
pip install onnx


If you are building ONNX from source on Windows, it is recommended that you also build Protobuf locally as a static library. The version distributed with conda-forge is a DLL, but ONNX expects it to be a static library.

Note that the instructions in this README assume you are using Visual Studio. It is recommended that you run all the commands from a shell started from "Developer Command Prompt for VS 2019" and keep the build system generator for cmake (e.g., cmake -G "Visual Studio 16 2019") consistent.

Build Protobuf and ONNX on Windows

Step 1: Build Protobuf locally ``` git clone cd protobuf git checkout v3.11.3 cd cmake

Explicitly set -DprotobufMSVCSTATIC_RUNTIME=OFF to make sure protobuf does not statically link to runtime library


For example:

cmake -G "Visual Studio 16 2019" -A x64 -DprotobufMSVCSTATICRUNTIME=OFF -DprotobufBUILDTESTS=OFF -DprotobufBUILDEXAMPLES=OFF -DCMAKEINSTALL_PREFIX=..\install

msbuild protobuf.sln /m /p:Configuration=Release msbuild INSTALL.vcxproj /p:Configuration=Release ```

Step 2: Build ONNX ```


git clone cd onnx git submodule update --init --recursive

Set environment variables to find protobuf and turn off static linking of ONNX to runtime library.

Even better option is to add it to user\system PATH so this step can be performed only once.

For more details check

set PATH=\bin;\include;\libs;%PATH% set USEMSVCSTATIC_RUNTIME=0

use the static installed protobuf


Optional: Set environment variable
for onnx-ml

Build ONNX

python install ```

If you would prefer to use Protobuf from conda-forge instead of building Protobuf from source, you can use the following instructions.

Build ONNX on Windows with Anaconda

# Use conda-forge protobuf
conda install -c conda-forge numpy libprotobuf=3.11.3 protobuf


git clone cd onnx git submodule update --init --recursive

Set environment variable for ONNX to use protobuf shared lib


Build ONNX

Optional: Set environment variable ONNX_ML=1 for onnx-ml

python install

Build ONNX on ARM 64

If you are building ONNX on an ARM 64 device, please make sure to install the dependencies appropriately.

pip install cython protobuf numpy
sudo apt-get install libprotobuf-dev protobuf-compiler
pip install onnx

Verify Installation

After installation, run

python -c "import onnx"

to verify it works.

Common Errors

Environment variables:

(should be 1 or 0, not ON or OFF)

CMake variables:



is ON then
must be OFF and
must be 0. If
is OFF then
must be ON and
can be 1 or 0.

Note that the

import onnx
command does not work from the source checkout directory; in this case you'll see
ModuleNotFoundError: No module named 'onnx.onnx_cpp2py_export'
. Change into another directory to fix this error.

Building ONNX on Ubuntu works well, but on CentOS/RHEL and other ManyLinux systems, you might need to open the CMakeLists file and replace all instances of


If you want to build ONNX on Debug mode, remember to set the environment variable

. For debug versions of the dependencies, you need to open the CMakeLists file and append a letter
at the end of the package name lines. For example,
NAMES protobuf-lite
would become
NAMES protobuf-lited

You can also use the onnx-dev docker image for a Linux-based installation without having to worry about dependency versioning.


ONNX uses pytest as test driver. In order to run tests, you will first need to install pytest:

pip install pytest nbval

After installing pytest, use the following command to run tests.



Check out the contributor guide for instructions.


Apache License v2.0

Code of Conduct

ONNX Open Source Code of Conduct

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