libcst
A concrete syntax tree with AST-like properties for Python 3.0 through 3.15 programs.
Decision gist · record as of 2026-08-14
Yes. libcst is actively maintained, has no known vulnerabilities, and is widely used (top 1000 on PyPI with ~52M monthly downloads). Install friction is moderate due to the native extension, but binary wheels cover common platforms. Choose it if you need to parse and modify Python code while preserving formatting; skip it if you only need syntax analysis and don't care about whitespace or comments.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.9 or later; if a binary wheel is unavailable for your platform, you need a Rust toolchain (cargo) to build the native parser extension.
- Medium install friction due to a native Rust extension; binary wheels are provided for Linux/Windows x86/x64 and macOS x64/arm64, but systems without a matching wheel require a Rust toolchain.
- The package is actively maintained with a recent release and no known vulnerabilities.
License · maintenance · safety
permissive license (permissive) — Permissive multi-license: MIT for all contributions, with dual MIT/PSF licensing for files derived from Python's standard library and Apache 2.0 for dataclasses-derived code. No restrictions on commercial or proprietary use.
last release 2026-07-29 (16 days) · last repo commit 2026-08-11 · 1,935 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 51,948,301 downloads/mo, #566 on PyPI
Alternatives
Verify before relying
import libcst as cst
from libcst.tool import dump
code = "1 + 2"
tree = cst.parse_expression(code)
print(dump(tree))- Performance characteristics and scalability limits for parsing very large codebases or deeply nested expressions.
- Memory overhead compared to the standard ast module for typical use cases.
- Specific version support claim for Python 3.15 (marked as supported but may be in pre-release).
What it is and what it does
libcst is a lossless parser that converts Python source code into a concrete syntax tree (CST) while preserving every formatting detail—comments, whitespace, parentheses, and line breaks. Unlike Python's built-in ast module, which discards formatting information, libcst reconstructs the original source exactly, making it ideal for tools that need to modify code and write it back without losing style or comments.
The library is designed for building automated refactoring tools (codemods) and linters that must understand code structure while respecting the developer's formatting choices. It depends on pyyaml, pyyaml-ft, and typing-extensions, and ships with a native Rust parser for performance. It supports Python 3.9 through 3.15 and is actively maintained by Meta.
Use it for
- Build automated refactoring tools that rewrite Python code while preserving comments and formatting.
- Implement linters that analyze code structure and report issues without losing the original source layout.
- Create code migration scripts that transform legacy Python to modern syntax while maintaining readability.
- Develop IDE plugins or language servers that need to understand and modify Python source with fidelity.
- Write code generation or templating tools that must integrate generated code into existing files cleanly.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
libcst is actively maintained, has no known vulnerabilities, and is widely used (top 1000 on PyPI with ~52M monthly downloads). Install friction is moderate due to the native extension, but binary wheels cover common platforms. Choose it if you need to parse and modify Python code while preserving formatting; skip it if you only need syntax analysis and don't care about whitespace or comments.
Install
libcst on PyPI
Before you install
Medium install friction due to a native Rust extension; binary wheels are provided for Linux/Windows x86/x64 and macOS x64/arm64, but systems without a matching wheel require a Rust toolchain. The package is actively maintained with a recent release and no known vulnerabilities.
Requires Python 3.9 or later; if a binary wheel is unavailable for your platform, you need a Rust toolchain (cargo) to build the native parser extension.
License in practice
Permissive multi-license: MIT for all contributions, with dual MIT/PSF licensing for files derived from Python's standard library and Apache 2.0 for dataclasses-derived code. No restrictions on commercial or proprietary use.
Quickstart
import libcst as cst
from libcst.tool import dump
code = "1 + 2"
tree = cst.parse_expression(code)
print(dump(tree))Verify before relying
- Performance characteristics and scalability limits for parsing very large codebases or deeply nested expressions.
- Memory overhead compared to the standard ast module for typical use cases.
- Specific version support claim for Python 3.15 (marked as supported but may be in pre-release).
Package facts
| License | permissive license permissive |
| Python support | Supports the current Python release >=3.9 |
| Install friction | Medium. Platform-specific wheel |
| Runtime dependencies | 3 packagespyyamlpyyaml-fttyping-extensions |
| Maintenance | Actively maintained 16 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 51,948,301 / month, #566 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | License :: OSI Approved :: MIT LicenseProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: 3.15Programming Language :: Python :: 3.9Programming Language :: Python :: Free ThreadingTopic :: Software Development :: LibrariesTyping :: Typed |
Evidence: libcst-1.9.0-cp310-cp310-macosx_11_0_arm64.whl; libcst-1.9.0-cp310-cp310-manylinux_2_28_aarch64.whl; libcst-1.9.0-cp310-cp310-manylinux_2_28_x86_64.whl; libcst-1.9.0-cp310-cp310-musllinux_1_2_aarch64.whl; libcst-1.9.0-cp310-cp310-musllinux_1_2_x86_64.whl; libcst-1.9.0-cp310-cp310-win_amd64.whl; libcst-1.9.0-cp310-cp310-win_arm64.whl; libcst-1.9.0-cp311-cp311-macosx_11_0_arm64.whl; libcst-1.9.0-cp311-cp311-manylinux_2_28_aarch64.whl; libcst-1.9.0-cp311-cp311-manylinux_2_28_x86_64.whl; libcst-1.9.0-cp311-cp311-musllinux_1_2_aarch64.whl; libcst-1.9.0-cp311-cp311-musllinux_1_2_x86_64.whl; libcst-1.9.0-cp311-cp311-win_amd64.whl; libcst-1.9.0-cp311-cp311-win_arm64.whl; libcst-1.9.0-cp312-cp312-macosx_11_0_arm64.whl; libcst-1.9.0-cp312-cp312-manylinux_2_28_aarch64.whl; libcst-1.9.0-cp312-cp312-manylinux_2_28_x86_64.whl; libcst-1.9.0-cp312-cp312-musllinux_1_2_aarch64.whl; libcst-1.9.0-cp312-cp312-musllinux_1_2_x86_64.whl; libcst-1.9.0-cp312-cp312-win_amd64.whl
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