A fast FDTD solver

electromagnetics, fdtd, pydantic, python, simulation, xarray
pip install tidy3d-beta==1.4.1



Notebooks tests Documentation Status PyPI version shields.io

Tidy3D is a software product from Flexcompute that enables large scale electromagnetic simulation using the finite-difference time-domain (FDTD) method.

This repository stores the python interface for Tidy3d.

This code allows you to:

  • Programmatically define FDTD simulations.
  • Submit and magange simulations running on Flexcompute's servers.
  • Download and postprocess the results from the simulations.

You can find a detailed documentation and API reference here. The source code for our documentation is here.


Signing up for tidy3d

Note that while this front end package is open source, to run simulations on Flexcompute servers requires an account with credits. You can sign up for an account here. After that, you can install the front end with the instructions below, or visit this page in our documentation for more details.

Installing the front end

To install the Tidy3D Python API locally, the following instructions should work for most users.

pip install --user tidy3d
tidy3d configure --apikey=XXX

Where XXX is your API key, which can be copied from your account page in the web interface.

In a hosted jupyter notebook environment (eg google colab), it may be more convenient to install and configure via the following lines at the top of the notebook.

!pip install tidy3d
import tidy3d.web as web

If those commands did not work, advanced installation instructions are below, which should help solve the issue.

Advanced Installation Instructions

Some users might require more a specialized installation, which we cover below.

Using pip (recommended)

The easiest way to install the tidy3d python interface is through pip.

pip install tidy3d

This will install the latest stable version.

To get a specific version x.y.z, including the "pre-release" versions, you may specify the version in the command as:

pip install tidy3d==x.y.z

Installing from source

Alternatively, for development purposes, eg. developing your own features, you may download and install the package from source as:

git clone https://github.com/flexcompute/tidy3d.git
cd tidy3d
pip install -e .

Configuring and authentication

With the front end installed, it must now be configured with your account information, which is done via an "API key".

You can find your API key in the web interface. After signing in and navigating to the account page by clicking the "Account Center" icon on the left-hand side. Then, click on the "API key" tab on the right hand side of the menu and copy your API key.

Note: We refer to your API specific API key value as XXX below.

To link your API key with Tidy3D, you may use one of three following options:

Command line (recommended)

The easiest way is through the command line via the tidy3d configure command. Run:

tidy3d configure

and then enter your API key XXX when prompted.

Note that Windows users must run the following instead (ideally in an anaconda prompt):

pip install pipx
pipx run tidy3d configure

You can also specify your API key directly as an option to this command using the api-key argument, for example:

tidy3d configure --apikey=XXX


Alternatively, you can manually set up the config file where Tidy3D looks for the API key. The API key must be in a file called .tidy3d/config located in your home directory, containing the following

apikey = "XXX"

You can manually set up your file like this, or do it through the command line line:

echo 'apikey = "XXX"' > ~/.tidy3d/config

Note the quotes around XXX.

Note that Windows users will most likely need to place the .tidy3d/config file in their C:\Users\username\ directory (where username is your username).

Environment Variable

Lastly, you may set the API key as an environment variable named SIMCLOUD_APIKEY.

This can be set up using


Note the quotes around XXX.

Testing the installation and authentication

Front end package

You can verify the front end installation worked by running:

python -c "import tidy3d as td; print(td.__version__)"

and it should print out the version number, for example:



To test the authentication, you may try importing the web interface via.

python -c "import tidy3d.web"

It should pass without any errors if the API key is set up correctly.

To get started, our documentation has a lot of examples for inspiration.

Issues / Feedback / Bug Reporting

Your feedback helps us immensely!

If you find bugs, file an Issue. For more general discussions, questions, comments, anything else, open a topic in the Discussions Tab.