JupyterLab Language Server Protocol (LSP)

5.3.0 · active · verified Fri Apr 17

jupyterlab-lsp integrates Language Server Protocol (LSP) features directly into JupyterLab, providing coding assistance like autocompletion, hover documentation, linting, and refactoring. As of version 5.3.0, it supports JupyterLab 4.x and is actively maintained with regular updates focusing on compatibility and new LSP features.

Common errors

```
Language Server not found: python
```
cause The Python language server (e.g., `python-lsp-server`) is not installed or not discoverable by `jupyterlab-lsp`.

fix Install the `python-lsp-server` package in the same environment as JupyterLab: `pip install 'python-lsp-server[all]'`.
```
Uncaught (in promise) Error: 404 Not Found
```
cause This error often indicates a problem with the JupyterLab server extension not being loaded correctly, an outdated frontend build, or an incorrect path for server components.

fix First, try rebuilding JupyterLab assets: `jupyter lab build`. If the issue persists, verify that `jupyterlab-lsp` is enabled (`jupyter labextension list` and `jupyter server extension list`) and restart your JupyterLab server. Clear your browser cache.
```
ModuleNotFoundError: No module named 'jupyterlab_lsp'
```
cause The `jupyterlab-lsp` Python package is not installed in the active Python environment where JupyterLab is running.

fix Install the package: `pip install jupyterlab-lsp`.

Warnings

breaking Major versions of `jupyterlab-lsp` are tightly coupled to major versions of `JupyterLab`. For example, `jupyterlab-lsp` 4.x is for `JupyterLab` 4.x, and `jupyterlab-lsp` 3.x is for `JupyterLab` 3.x. Installing an incompatible version can lead to errors or the extension not loading.
Fix: Ensure your `jupyterlab-lsp` version matches your `JupyterLab` major version. Upgrade both simultaneously or check the compatibility matrix on the official GitHub page.
gotcha After installing `jupyterlab-lsp`, users often expect immediate coding assistance for all languages. However, `jupyterlab-lsp` itself only provides the framework; each language (e.g., Python, R, TypeScript) requires its own specific language server to be installed separately.
Fix: Install the appropriate language server for your desired language. For Python, `pip install 'python-lsp-server[all]'` is commonly used. For other languages, consult the `jupyterlab-lsp` documentation.
gotcha Sometimes, after installing or upgrading `jupyterlab-lsp` or other JupyterLab extensions, the frontend assets might become stale or cached incorrectly, leading to features not appearing or errors in the browser console.
Fix: Try running `jupyter lab build` in your terminal to rebuild the frontend assets. Additionally, clear your browser cache (Ctrl+Shift+R or Cmd+Shift+R) and restart your JupyterLab server.

Install

pip install jupyterlab-lsp Install core extension
pip install 'python-lsp-server[all]' Install Python language server (recommended for Python users)

Quickstart

This Python code, when opened in a `.py` file or a notebook within JupyterLab (after `jupyterlab-lsp` and `python-lsp-server` are installed), will demonstrate LSP features. You'll see type hints, signature help, hover documentation, and autocompletion provided by the extension.

# hello_lsp.py
import os

def greet(name: str) -> str:
    """
    Returns a greeting message.
    Hover over 'greet' for documentation.
    Type 'greet(' to see signature help.
    """
    message = f"Hello, {name}!"
    # Type 'message.' to trigger autocompletion provided by LSP
    return message.upper()

if __name__ == '__main__':
    user_name = os.environ.get('USER_NAME', 'World')
    print(greet(user_name))

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