# Poly Lint Format

> Reference for poly, the single-binary multi-language linter and formatter — per-language engines, the lint/fmt commands, poly.toml configuration, severity behavior, and the shared CI validation workflow. Load when linting or formatting code, configuring poly.toml, or wiring poly into CI.

- Skill: `kreuzberg-dev/poly-lint-format` (Agent Skill)
- Install (CLI): `npx skillmds@latest add kreuzberg-dev/poly-lint-format`
- Raw SKILL.md: https://api.skillmd.com/api/skills/kreuzberg-dev/poly-lint-format/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Productivity
- Author: kreuzberg-dev (https://skillmd.com/u/kreuzberg-dev)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/kreuzberg-dev/poly-lint-format

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# Poly

Poly is a single-binary multi-language linter and formatter. It bundles language engines (ruff for Python, oxc for JS/TS/JSON, taplo for TOML, rumdl for Markdown) and delegates to native tools (cargo fmt, cargo clippy, golangci-lint, actionlint, shellcheck, shfmt) when present. Most repos need no extra toolchains. Configure via per-repo `poly.toml`.

## Engines by language

| Scope | Engine(s) |
|-------|-----------|
| **Python** | ruff (lint + format), pyrefly (type check) |
| **JS/TS/JSON/CSS** | oxc (lint + format) |
| **TOML** | taplo (lint + format) |
| **Markdown** | rumdl (format) |
| **Rust** | cargo fmt + cargo clippy (via cargo hook) |
| **Go** | golangci-lint |
| **Java** | checkstyle, maven verify |
| **Ruby** | rubocop (format + lint) |
| **C#** | dotnet format |
| **PHP** | php-cs-fixer, phpstan |
| **Elixir** | mix format, mix credo |
| **R** | styler, lintr |
| **C/C++** | clang-format, cppcheck |
| **Shell** | shfmt, shellcheck |
| **Git** | gitfluff (commit message linting), ai-rulez-generate |
| **GH Actions** | actionlint |
| **Helm/K8s** | helm-lint, kubeconform |

## Commands

- Lint: `poly lint .`
- Check formatting (dry-run): `poly fmt --check .`
- Apply formatting: `poly fmt --fix .`
- Apply lint autofixes: `poly lint --fix .`

## Configuration

Per-repo `poly.toml` defines linting and formatting rules:

- `[discovery]` — exclude globs
- `[lint.<lang>.<tool>]` — select/ignore rules, settings like `pydocstyle_convention`, `line_length`
- `[per-file-ignores]` — file-specific exemptions
- `[fmt.<lang>.<tool>]` — formatter options
- `[hooks.builtin]` — git hook configuration

Cache directory `.polylint/` is gitignored.

## Severity

`poly lint` exits non-zero only on error-severity findings. Warnings are reported but do not fail CI.

## CI

Run linting and formatting validation in CI via the shared reusable workflow:

```yaml
uses: xberg-io/actions/.github/workflows/reusable-validate.yml@v1
```

This workflow runs `poly fmt --check .` then `poly lint .` with optional inputs `setup-rust` and `setup-python`.

Always run `poly fmt --check .` and `poly lint .` after making changes to verify compliance.