Arity

Arity is a language server, formatter, and linter for the R programming language, built on a lossless, incremental parser. It provides a fast, deterministic development experience that integrates with popular code editors and IDEs.

• Formatter: deterministic, rule-based formatting based on the tidyverse style guide, with idempotent output and support for roxygen and DESCRIPTION (.dcf) files.
• Linter: project-aware linting, with correctness, readability, and performance rules, many with safe autofixes.
• Language server: formatting, diagnostics with quick fixes, hover, completion, signature help, go-to-definition and references, rename, document and workspace symbols, semantic tokens, folding, and call hierarchy.

Installation

Arity is available from several sources:

• CRAN: install.packages("arity") in R (formatter bindings; see R package usage)
• crates.io: cargo install arity
• Homebrew: brew install jolars/tap/arity
• npm: npm install -g arity-cli (bundles a prebuilt binary)
• PyPI: uv tool install arity/pipx install arity
• mise/Aqua: see the installation guide
• Prebuilt binaries: from the releases page
• VS Code/Open VSX: the Arity extension (also works in Positron)
• Arch Linux: paru -S arity-bin (or another AUR helper; packages: arity-bin, arity)
• NixOS: the arity package is available in nixpkgs

Install Script

The installer scripts pick the right release artifact for your platform and install to a user-local directory by default. They download the matching Arity CLI release asset and verify its checksum. If you prefer, download and inspect the script before running it.

For macOS and Linux:

curl --proto '=https' --tlsv1.2 -sSf https://arity.cc/install | sh

For Windows PowerShell:

powershell -NoProfile -ExecutionPolicy Bypass -Command "irm https://arity.cc/install.ps1 | iex"

Set ARITY_INSTALL_DIR to change the destination, ARITY_TAG to pin a version, ARITY_LIBC (gnu or musl) to override the detected libc on Linux, and ARITY_VERIFY_CHECKSUM=false to skip checksum verification.

Usage

# Format in place
arity format file.R

# Verify formatting without writing
arity format --check src/

# Lint a project directory
arity lint src/

# Fix lint findings in place
arity lint --fix file.R

arity lint reads from stdin when given - (or when piped with no paths), and exits non-zero when it reports any findings.

Configuration

Configure Arity with arity.toml, which is discovered by walking up from each file's directory to the repository root. Run arity init to scaffold a commented starter file. See the configuration reference for every key.

Editor Integration

arity lsp starts a stdio-based language server offering formatting, diagnostics with quick fixes, hover, completion, signature help, go-to-definition and references, rename, document and workspace symbols, semantic tokens, folding, and call hierarchy.

The Arity extension for VS Code/Open VSX (and Positron) bundles the binary and starts the server automatically. For Neovim, Helix, and other editors, see the editor setup guide.

In RStudio, the development R package provides a Format with arity addin for selections and unsaved documents. The CRAN package supports formatting saved files from the console. See RStudio setup for installation and configuration.

Pre-Commit Hook

arity-pre-commit provides pre-commit hooks for linting and formatting. It installs a prebuilt binary wheel from PyPI, so no Rust toolchain or R installation is required:

repos:
  - repo: https://github.com/jolars/arity-pre-commit
    rev: v0.25.0
    hooks:
      - id: arity-lint
      - id: arity-format

See the integration guide for file coverage, optional fixes, and updates.

GitHub Actions

arity-action installs Arity and runs format and lint checks in CI:

jobs:
  arity:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v6
      - uses: jolars/arity-action@v1

Crates

The parsing and formatting engines are published as standalone crates for use in other tools: arity-parser (lossless CST parser, typed AST wrappers, incremental reparser) and arity-formatter (the formatter, with optional serde/schemars support for embedders). Both are versioned independently of the CLI.

Acknowledgements

The core architecture of Arity is entirely based on rust-analyzer, using salsa for incremental computation and rowan for lossless syntax trees. Arity also owes a great debt to air, on which it is heavily inspired and from which it has borrowed tests, rules, and formatting style. It is also inspired by jarl and has borrowed rules from it as well as some of its architecture.

Documentation

Full documentation lives at arity.cc:

• Getting started
• Editor setup
• Configuration
• CLI reference
• Lint rules