# Limitations

xlwings Lite is based on [Pyodide](https://pyodide.org), and comes with the following limitations:

- Packages that depend on the `multiprocessing` or `threading` modules aren’t currently supported.
- Some packages may need to be built specifically for Pyodide if they aren’t available yet and if they aren’t pure Python packages, see [Creating a Pyodide package](https://pyodide.org/en/stable/development/new-packages.html). For a list of “complex” packages that are available for Pyodide, see [Packages built in Pyodide](https://pyodide.org/en/stable/usage/packages-in-pyodide.html).
- Web APIs: Often, you’ll run into CORS issues as the server needs to explicitly allow access via headers. GitHub works though so you can access files from there. Otherwise, you could use a CORS proxy (preferably owned by you) to work around this issue if you have no control over the web server, see [Web API Requests](web-requests.md)
- TCP/IP connections: TCP/IP connections aren’t supported, which means that you can’t directly connect to databases like PostgreSQL. SQLite, however, is supported, see [Databases](databases.md).
- Pyodide currently has a memory limit of 2GB.
- There is currently no debugger.

See the [Pyodide docs](https://pyodide.org/en/stable/usage/wasm-constraints.html) for further details.