Badness

Badness is a language server, formatter, and linter for LaTeX, built on a lossless concrete syntax tree.

It parses LaTeX once and serves three tools from that tree:

• Formatter (badness format): deterministic, rule-based layout.
• Linter (badness lint): diagnostics with source snippets.
• Language server (badness lsp): both, live in your editor.

The architecture follows rust-analyzer: a generic, error-tolerant, hand-written parser produces a lossless tree, semantics are layered on top as a separate concern, and recomputation is incremental. badness never requires resolving macros or catcodes to succeed—anything it cannot statically recognize degrades to generic nodes rather than a crash. Two properties hold by construction and are enforced as tests: losslessness (the tree reconstructs the input byte-for-byte) and idempotence (formatting an already formatted file changes nothing).

Installation

Badness is available from several sources:

• crates.io: cargo install badness
• npm: npm install -g badness (bundles a prebuilt binary)
• PyPI: uv tool install badness/pipx install badness
• Prebuilt binaries: from the releases page
• VS Code/Open VSX: the Badness extension (also works in Positron and Cursor)
• From source: cargo install --path . in a checkout

The VS Code/Open VSX extension bundles the badness binary and starts the language server automatically when you open a .tex file.

Usage

# Format a file in place (or stdin → stdout with no path)
badness format paper.tex

# Verify formatting without writing—exits non-zero if anything would change
badness format --check paper.tex

# Lint, reporting parse diagnostics
badness lint paper.tex

# Run the language server over stdio
badness lsp

Formatting is configurable via a TOML file named badness.toml. See the documentation for the full reference.

The language server runs over stdio (badness lsp); see the editor setup guide for Neovim and VS Code wiring.

Pre-commit hook

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

repos:
  - repo: https://github.com/jolars/badness-pre-commit
    # badness version
    rev: v0.11.0
    hooks:
      # Lint .tex, .sty, .cls, .dtx, .ins, and .bib files
      - id: badness-lint
      # Format the same files in place
      - id: badness-format

GitHub Actions

badness-action installs badness and runs format and lint checks in CI:

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

Documentation

Full documentation lives at https://badness.dev/ (built with mdBook from docs/).

Contributing

See CONTRIBUTING.md.

License

MIT