lark

a modern parsing library

lark Permissive license MIT Active ★ 5,954 v1.3.1 released 2025-10-27

Install

lark on PyPI

pip

pip install lark

uv

uv add lark

poetry

poetry add lark

Package facts

License	MIT (permissive)
Python support	supports the current Python release (>=3.8)
Install friction	low — pure-Python wheel
Runtime dependencies	none
Maintenance	actively maintained — 290 days since the last release
Last repo commit	2026-08-13
First released	2020-10-13
Popularity	one of the top 1,000 most-downloaded packages on PyPI (30-day window, as of 2026-08-13)
Known vulnerabilities	none known (OSV.dev, checked 2026-08-13)

Evidence: lark-1.3.1-py3-none-any.whl

Keywords: Earley, LALR, parser, parsing, ast

Development Status :: 5 - Production/StableIntended Audience :: DevelopersLicense :: OSI Approved :: MIT LicenseProgramming Language :: Python :: 3Topic :: Software Development :: Libraries :: Python ModulesTopic :: Text Processing :: GeneralTopic :: Text Processing :: Linguistic

About lark

from the package's own PyPI description — quoted content, verbatim

Lark is a modern general-purpose parsing library for Python. With Lark, you can parse any context-free grammar, efficiently, with very little code. Main Features: - Builds a parse-tree (AST) automagically, based on the structure of the grammar - Earley parser - Can parse all context-free grammars - Full support for ambiguous grammars - LALR(1) parser - Fast and light, competitive with PLY - Can generate a stand-alone parser - CYK parser, for highly ambiguous grammars - EBNF grammar - Unicode fully supported - Automatic line & column tracking - Standard library of terminals (strings, numbers, names, etc.) - Import grammars from Nearley.js - Extensive test suite - And much more! Since version 1.2, only Python versions 3.8 and up are supported.

Read as markdown · JSON record · Source repository · Homepage

AI interpretation — verify before relying

AI-generated interpretation of the package facts above; every digit, version, license, or vulnerability id it cites is grounded in the facts already shown on this page

Lark is a parsing library that builds abstract syntax trees from context-free grammars using Earley, LALR(1), or CYK parsers, supporting ambiguous grammars and EBNF syntax with full Unicode support.

Lark has zero runtime dependencies and ships as a pure Python wheel, making installation frictionless. The project is actively maintained with a recent release (290 days ago) and strong community engagement (5954 GitHub stars).

Lark is licensed under MIT (permissive), allowing free use, modification, and distribution in both open-source and commercial projects with minimal restrictions.

Usage

pip install lark==1.3.1

from lark import Lark

grammar = r'''
    start: "hello" NAME
    NAME: /\w+/
'''
parser = Lark(grammar)
tree = parser.parse("hello world")
print(tree.pretty())

Requires Python 3.8 or higher; only Python 3.8+ versions are supported as of version 1.2.

Verdict: Lark is a production-ready, actively maintained parsing library with no dependencies, permissive licensing, and zero known vulnerabilities. It is well-suited for projects requiring flexible grammar-based parsing with minimal installation overhead.

Needs verification

Performance characteristics relative to other parsing libraries in real-world use cases
Completeness of documentation and community support resources beyond the GitHub repository

context-free grammar parserparse tree AST generatorEarley LALR parser libraryambiguous grammar parsingEBNF parser pythonstandalone parser generationlinguistic parsing library