Basilisk is an open-source Python language server and type checker focused on full compliance with Python's typing specification. It is distinguished by achieving a 100% conformance score on the official python/typing suite, passing all 141 tests with no false positives or missed required errors. The tool is designed for Python developers seeking precise type checking, language server features, and integrated debugging, all within a single environment.
Developed in Rust, Basilisk offers a complete development environment that includes a type checker, language server, debugger, and profiler. Its language server protocol (LSP) implementation supports features such as autocomplete, go-to-definition, hover, refactoring, diagnostics, and integrated debugging. The platform is compatible with popular editors, providing official extensions for VS Code, Cursor, Zed, and Neovim, with JetBrains support planned. Basilisk is strict by default but also offers eight opt-in strictness rules that make type annotations mandatory at various code points; these rules can be enabled per file or path through the editor or a configuration file, and each comes with quick-fix options for rapid adoption.
Performance is a key aspect, with Basilisk posting an 11 ms median cold full-file check in benchmarks, which is the lowest among all measured Python type checkers. Incremental re-checks are supported, analyzing only edited files and their importers for efficient workflow. The tool also provides a suite of quick fixes and refactoring capabilities, such as extracting, inlining, changing signatures, and moving symbols, with many diagnostics offering one-keystroke corrections.
Basilisk is distributed under the MIT License, ensuring that it remains fully open source and free from proprietary lock-in. It does not require a runtime dependency, and every release is benchmarked and graded against the latest official python/typing suite to ensure continued conformance. This makes Basilisk a suitable choice for developers and teams who prioritize standards compliance, performance, and an integrated Python development experience.
basilisk-python sits in PulseGate's Developer Tools category. It focuses on ensuring Python code correctness and type safety through strict static analysis. It is built as an open-source project for python developers. basilisk-python is open source under the MIT license. The product ships for the web and the command line.
Nimblesite builds and maintains basilisk-python, and the product first shipped in 2026. Development happens publicly on GitHub with 93 commits in the last 90 days. PulseGate's similarity index finds few close equivalents — basilisk-python occupies a relatively distinct niche. Key capabilities include type checking, LSP support, and strict mode.
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