---
id: arpeggio
version: "2.0.3"
license: MIT
license_treatment: permissive
maintenance: active
---

# Arpeggio — Packrat parser interpreter

License: permissive · Maintenance: active · Downloads: 2.1M/mo

## What it is and what it does

Arpeggio is a parser library that implements Packrat parsing using Parsing Expression Grammars (PEG). It uses recursive descent with memoization to parse input according to user-defined grammar rules. The library is designed for developers who need to build parsers for domain-specific languages, configuration formats, or other structured text without writing hand-coded parsing logic.

The package has no runtime dependencies and is marked as Production/Stable. It supports Python 3.6 through 3.10 and has been actively maintained since its first release in 2014-08-16. The documentation notes that textX provides a higher-level interface to Arpeggio if you need a more convenient API for language definition.

Use it for:

- Build a parser for a custom configuration file format or domain-specific language
- Parse structured text data where you want to define grammar rules declaratively rather than write parsing code
- Create an interpreter or compiler frontend that needs to consume and validate input against a formal grammar
- Extract and transform data from text files with complex, nested structures

## Worth the install?

AI-flagged interpretation of the facts above — verify before relying.

Arpeggio is a recursive descent parser with memoization that implements PEG (Packrat) grammars, letting you define and parse custom languages or structured text formats.

Yes. Arpeggio is a stable, actively maintained parser library with no dependencies and permissive licensing. Install it if you need to build a parser for a custom grammar or language; if you want a higher-level interface for language definition, consider textX instead.

## Install

pip install arpeggio
uv add arpeggio
poetry add arpeggio

## Installing Arpeggio

Before you install: Low install friction with no runtime dependencies. Active maintenance with a recent release in 2025-09-12 and last commit on 2026-08-02; the repository is not archived and has 288 stars.

License in practice: MIT license is permissive, allowing use in commercial and proprietary projects with minimal restrictions beyond attribution.

Quickstart:

pip install arpeggio

from arpeggio import ParsingExpression, ZeroOrMore, OneOrMore, Optional
from arpeggio import PTNodeVisitor, visit_parse_tree

# Define a simple grammar and parse input
grammar = OneOrMore(ParsingExpression(...))
parse_tree = grammar.parse(input_string)

Verify before relying:

- Whether Arpeggio handles left-recursive grammars or has known limitations with certain PEG patterns
- Performance characteristics when parsing large inputs or deeply nested structures
- Whether the package includes built-in error recovery or reporting mechanisms

## Package facts

- License: MIT (permissive)
- Python support: unspecified
- Install friction: low
- Maintenance: active
- Downloads: 2.1M/month (top 5,000 on PyPI)
- Known vulnerabilities: none known

## Tags

PEG parser, recursive descent parser, packrat parser, grammar-based parsing, language parser library, text parsing, DSL parser, parsing, peg-grammar, compiler-tools

[View on SkillFed](https://skillfed.io/packages/arpeggio) · [View on PyPI](https://pypi.org/project/arpeggio/)