Basilisk for VS Code

The open-source Pylance replacement for VS Code.
Complete language server: diagnostics, autocomplete, hover, go-to-definition,
refactoring, debugging, profiling. Strict by default. Built in Rust.

Website  •  Quick Start  •  Rules  •  GitHub

What Basilisk does

Basilisk is a complete Python language server and VS Code extension that replaces Pylance and Pyright. It is not just a type checker — it provides autocomplete, go-to-definition, hover, code actions, refactoring, integrated debugging, and profiling. All fully open source.

Other type checkers default to permissive and hope you opt into strictness. Basilisk starts strict and stays strict. If your code isn't typed, it's an error.

error[BSK-E0001]: Missing parameter type annotation for `name`
  --> greet.py:1:10
   |
 1 | def greet(name):
   |           ^^^^
   |
   = help: Add a type annotation: `name: <type>`

error[BSK-E0002]: Missing return type annotation
  --> greet.py:1:1
   |
 1 | def greet(name):
   | ^^^^^^^^^^^^^^^^

Fix it once. Ship it typed forever:

def greet(name: str) -> str:
    return "Hello " + name

Features

Real-time diagnostics

Errors appear inline as you type — powered by the Basilisk LSP server with sub-10ms incremental analysis via the Salsa framework (same tech as rust-analyzer).

Autocomplete, hover, go-to-definition

Full language intelligence — completions, hover documentation, go-to-definition, find references, rename symbol.

Code actions and refactoring

Extract function/variable, rename, move symbol, inline, organize imports — all built into the LSP.

Integrated debugging

Press F5 to debug Python. Basilisk spawns debugpy and brokers the DAP connection — breakpoints, stepping, variable inspection, watch expressions. No separate debug extension needed.

Integrated profiling

Profile Python code with py-spy directly from the editor. View heatmaps and identify bottlenecks without leaving VS Code.

Activity panel

The Basilisk sidebar provides three panels accessible from the activity bar:

Module Explorer — Browse your workspace's Python module tree. Each module shows its top-level symbols (functions, classes, variables) with type annotation status. Right-click to copy import paths. Toggle between tree and flat views. Filtered by glob patterns.

Type Health — Workspace-wide type coverage dashboard. Shows annotated vs unannotated symbol counts, error/warning tallies, and per-module coverage percentages with color-coded progress bars. Sort by worst-first, best-first, or alphabetical.

Basilisk Info — Feature status toggles (type checking, inlay hints, Ruff, debugger, test explorer, uv), quick actions (restart server, organize imports), and server info (version, binary path, analysis mode).

All panels update automatically when files change (debounced 300ms). The Module Explorer and Type Health panels appear when a workspace is open; the Info panel is always visible.

Inlay hints

See inferred types and parameter names directly in your editor:

• Parameter names at call sites
• Variable types for unannotated locals

Ruff integration

Built-in support for Ruff formatting and import organization. One extension, two tools.

Single binary, zero dependencies

Basilisk ships as one Rust binary. No Python runtime, no Node.js, no pip, no npm. Install it and go.

Diagnostic rules

All rules are on by default. There is no way to relax them globally.

Annotation rules

Type correctness

How it compares

Extension settings

Commands

Requirements

Install the Basilisk binary:

cargo install basilisk

Rust 1.87+ required for building from source.

Part of Basilisk

This is the VS Code extension for the Basilisk project. Basilisk also supports Neovim and Zed.

License

MIT or Apache-2.0, at your option.

Built by NIMBLESITE PTY LTD.