Poly

One binary. ~30 languages. No toolchain to install.

poly lints and formats whole repositories in seconds: curated Rust backends for the languages that matter, a tree-sitter fallback for everything else, and a Claude/Codex plugin plus an MCP server so agents can drive it directly instead of shelling out.

Lint + format · one poly.toml · pure Rust, zero deps · blake3 cache + rayon parallelism · git hooks & commit checks · MCP + Claude/Codex plugin

[](https://github.com/Goldziher/poly/actions/workflows/ci.yaml) [](LICENSE) [](https://goldziher.github.io/poly)

[Install](#installation) · [What You Get](#what-you-get) · [What Runs Out of the Box](#what-runs-out-of-the-box) · [AI Agents & MCP](#ai-agents--mcp) · [Performance](#performance) · Docs · [Contributing](#contributing)

---

What You Get

| Capability | What it does | |---|---| | Fast on real repos | Lints Django in 0.82s and home-assistant's 25,000 files in 3.5s, cold cache; see [Performance](#performance). | | One binary, no toolchain | ~30 languages with native Rust backends (ruff, oxc, biome, mago, taplo, rumdl, sqruff, malva, markup_fmt, rubyfmt, …) plus a tree-sitter tier for everything else. No Node, Python, or Ruby needed. | | Built for agents | A Claude/Codex plugin and a stdio MCP server ship in the box — an agent calls poly's tools directly instead of shelling out and parsing text. See [AI Agents & MCP](#ai-agents--mcp). | | One config | poly.toml drives linting, formatting, git hooks, and commit-message policy. | | Cache + parallelism | A blake3 content-hash cache skips unchanged work; rayon parallelizes the rest across cores. | | Git hooks & commit checks | poly hooks install wires lint, format, and Conventional-Commit checks into git — no external hook framework. | | Two lint tiers on every language | A code-quality metrics engine and a built-in 26-rule ast-grep pack (13 rules on by default) run on top of the backends above, at warning severity so they never redden an unconfigured CI. | | Simple distribution | Prebuilt binaries via a shell/PowerShell installer, a GitHub Action, Homebrew, Scoop, npm, and PyPI. |

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Installation

Quick install

curl -fsSL https://raw.githubusercontent.com/Goldziher/poly/main/install.sh | sh

Windows PowerShell:

irm https://raw.githubusercontent.com/Goldziher/poly/main/install.ps1 | iex

Both detect the platform, download the matching release archive, and verify it against sha256sums.txt. Set POLY_VERSION=0.23.1 to pin an exact release.

GitHub Actions

- uses: Goldziher/poly@v0
  with:
    version: v0.23.1 # omit for the latest release

Forwards to install.sh and caches the installed binary by version and platform. See [ACTION_USAGE.md](ACTION_USAGE.md) for the full input/output reference.

Package managers

brew install Goldziher/tap/poly

scoop bucket add goldziher https://github.com/Goldziher/scoop-bucket
scoop install poly

Homebrew's tap is a single rolling formula with no versioned alias yet — treat it as a get-latest channel and use the installer script or the GitHub Action where a pinned version matters. cargo binstall --git https://github.com/Goldziher/poly poly-cli also works, resolving the same GitHub release archives.

npm and PyPI

npm i -g @goldziher/polylint
pip install polylint

Both install the same prebuilt poly binary. The package is named polylint (the unscoped poly name belongs to unrelated projects on both registries), but the executable is poly on every channel — polylint also works everywhere as an alias for the same binary. Full per-platform detail in [docs/INSTALL-PACKAGES.md](docs/INSTALL-PACKAGES.md).

As an agent plugin

poly ships its own Claude/Codex plugin, registering poly mcp as a stdio server plus 5 skills and 2 slash commands (/poly-check, /poly-fix):

/plugin marketplace add Goldziher/poly
/plugin install poly@poly

Codex: add the Goldziher/poly marketplace through your client's plugin manager (manifest at .codex-plugin/plugin.json). The plugin assumes poly is already on PATH — it does not bundle the binary — and its version tracks the poly binary version lock-step. See [AI Agents & MCP](#ai-agents--mcp).

As an MCP server

Any MCP-capable client can run poly directly:

{
  "mcpServers": {
    "poly": { "command": "poly", "args": ["mcp"] }
  }
}

---

Quickstart

$ poly lint
./app.py
  warning  ruff  T201  5:5  `print` found
  warning  ruff  ANN201  4:5  Missing return type annotation for public function `main`
  error  ruff  F401  1:8  `os` imported but unused

3 issues found.
  2 files linted
  1 issue fixable with the `--fix` option

$ poly fmt --check
would reformat ./src/main.rs

1 file will change.
  2 files checked

$ poly fmt --fix
reformatted ./src/main.rs

1 file reformatted.
  2 files checked

$ poly hooks install
✓ Installed 2 git hooks in .git/hooks
  › commit-msg
  › pre-commit

poly fmt is a dry run by default (CI-friendly); add --fix to write changes, and poly lint --fix to apply lint autofixes. poly hooks install wires the git hooks once — lint, format, and commit checks then run on every git commit.

Exit codes are a contract: 0 is clean, 2 means the run verified less than it claims, and 1 means findings — which for poly fmt --fix reports that files were rewritten, so a script running it in fix mode should treat 1 as success. Add -q to trim the per-file detail on a large repository; the summary keeps every count and reason.

---

Demos

Real recordings, not mockups — vhs runs each command live, so the timings on screen are the timings you get. Tapes are in [docs/media/tapes/](docs/media/tapes/).

Kubernetes: 31,303 files, one binary, no Go toolchain.

Django is not a Python repo — it is Python, JavaScript, CSS, HTML, TOML, YAML and Markdown. One tool, one config, one pass.

Every report has a machine-readable form. --format toon is compact enough to hand to an agent without burning its context; --format json is there when you want a document to parse.

And an agent can skip the terminal entirely. poly mcp speaks MCP over stdio and advertises the same eleven tools the CLI exposes.

---

How It Works

poly discovers files once (respecting .gitignore), plans the engine list once per language, and runs the per-file work in parallel on a rayon pool. Every backend — a linked-in Rust crate, the tree-sitter tier, or a wrapped CLI — returns the same Diagnostic and FormatOutput shapes, so reporting, caching, and MCP output stay uniform.

flowchart LR
  A["paths"]
  B["discovergitignore aware"]
  C["plan enginesper language"]
  D["rayon file loop"]
  E["blake3 cache"]
  F["lint / formatreports"]
  A --> B --> C --> D
  D |hit / miss| E
  D --> F

The default path needs no Python, Node, Go, or JVM — the backends are Rust crates compiled into the binary, and a language without a dedicated backend falls through to a tree-sitter generic tier that is still pure Rust. The result cache is keyed by file bytes, engine name, engine version, and resolved engine config, so a tool upgrade or a config change invalidates exactly the entries it affects. --debug prints per-file engine timing and cache hit/miss data.

---

What Runs Out of the Box

poly is useful with an empty poly.toml. This is what a run with no configuration actually does; anything opt-in is marked as such.

| Backend | What it enables by default | |---|---| | ruff (Python) | 22 selector groups: ruff's own F, E4, E7, E9, plus W6, I, UP, B, ANN, SIM, C4, RET, FURB, PERF, TRY, BLE, S110, C90, PLR, T20, TC, PTH, RUF, ARG. E1/E2/E3/W1/W2/W3 stay off because the formatter owns them, and seven noisy members are turned back off: B008, RUF100, ANN002, ANN003, ARG002, PLR2004, TRY003. Line length 120, docstring code formatted at width 120. | | oxlint (JS/TS) | oxlint's own default is correctness only. poly adds suspicious, pedantic, complexity, typescript/no-explicit-any, typescript/no-non-null-assertion and no-console, all at warning. restriction, style and nursery stay off; no-underscore-dangle, max-lines-per-function, max-lines and max-classes-per-file are turned back off. | | mago (PHP) | PHP 8.4, with six maintainability metrics downgraded from error to warning: cyclomatic-complexity (15), excessive-parameter-list (5), too-many-methods (10), too-many-properties (10), too-many-enum-cases (20), kan-defect (1). | | rumdl (Markdown) | Five rumdl-proprietary stylistic rules disabled, plus four more for MDX. Line length 120. | | biome (CSS/SCSS, GraphQL) | The correctness and suspicious rule groups. Accessibility, style, complexity, performance and security are opt-in. |

Three tiers that run on every language

• typos — spell-checks identifiers, comments and strings. Always on; it has no enable key.
• The code-quality engine — tree-sitter metric rules, listed below.
• The built-in ast-grep pack — 26 rules across C#, Elixir, Go, Java, Kotlin, Python, Ruby, Rust and Swift. **13

are on by default**; the other 13 ship severity: off and are one config line away. Your own rules under [rules] dirs sit above the pack — a rule with the same id replaces the built-in one outright.

A fourth cross-cutting engine, uncomment (comment removal), is off by default.

| Quality rule | Default | |---|---| | file-too-long | 1000 lines | | function-too-long | 80 lines | | type-too-long | 300 lines | | too-many-parameters | 6 | | nesting-too-deep | 4 | | cyclomatic-complexity | 20 | | lazy-ignore | on | | magic-number | opt-in — allows −1, 0, 1, 2, 10, 100 | | law-of-demeter | opt-in — chain depth 3 |

The quality engine never duplicates a backend rule: where ruff or oxlint already covers a metric, it defers. It counts as lint coverage only for languages whose control flow it can model — Python, Rust, Go, JavaScript, JSX, TypeScript, TSX, Java, Kotlin, C, C++, C# and Ruby — while other languages still get the line-count rules.

Everything these three tiers report is warning severity, and warnings alone do not fail a run, so turning poly on does not redden an unconfigured CI.

Native toolchain CLIs

gofmt, rustfmt and shellcheck run automatically when found on PATH; shellcheck is the only one of the three that lints. zig fmt, shfmt, google-java-format, ktfmt, styler (R), swift-format, dart format and gleam format are opt-in. When a tool is absent the language falls through to the tree-sitter tier, so the zero-dependency promise holds either way.

---

Backend Coverage

| Language | Backend | Lint | Format | |---|---|---:|---:| | Python | ruff | yes | yes | | JavaScript / TypeScript / JSX / TSX / JSON | oxc | yes | yes | | TOML | taplo | yes | yes | | YAML | saphyr + prettyyaml | yes | yes | | Markdown / MDX | rumdl | yes | yes | | SQL | sqruff | yes | yes | | CSS / SCSS | malva + biome | yes | yes | | Less | malva | no | yes | | GraphQL | graphql + biome | yes | yes | | PHP | mago | yes | yes | | HCL / Terraform | hcl | yes | yes | | HTML / Vue / Svelte / Astro / XML | markupfmt | no | yes | | Dockerfile | dockerfile | yes | no | | .env | dotenv | yes | no | | INI | ini | yes | no | | Ruby | rubyfmt | no | yes | | Nix | alejandra | no | yes | | Go | gofmt, automatic when installed | no | yes | | Rust | rustfmt, automatic when installed | no | yes | | Shell | shellcheck automatic, shfmt opt-in | yes | opt-in | | Zig / Java / Kotlin / R / Swift / Dart / Gleam | first-party CLI, opt-in | no | opt-in | | Everything else identified | tree-sitter generic tier | no | best effort |

The Lint column is the language's own backend; the three cross-cutting tiers add findings on top, including where that column says no. Beyond this table, an opt-in catalog of 348 tools across 175 languages covers the long tail. Full per-language reference: Backends.

---

AI Agents & MCP

poly ships its agent integration in the box rather than expecting one to be bolted on.

/plugin marketplace add Goldziher/poly
/plugin install poly@poly

That installs 5 skills and 2 slash commands (/poly-check, /poly-fix) that teach an agent poly's tiered backend model and when to reach for lint vs. format vs. hooks. Codex clients add the same marketplace through their own plugin manager.

poly mcp is a stdio MCP server exposing eleven tools that mirror the CLI 1:1 — lint, format_check, rules, config_show, cache_stats and version (read-only), lint_fix, format_write and cache_clean (mutating), and workspace_lint / workspace_lint_fix. The last two run the multi-minute whole-project phase (cargo clippy, cargo-sort, cargo-machete, cargo-deny) and are exposed as async Tasks: the call returns a handle the client polls with tasks/get, falling back to a synchronous result for clients that do not declare the capability.

Every result carries a poly identity block (version, build id, channel, executable, pid) and separates three per-file outcomes — checked, skipped (poly declined the file) and errored (poly failed on a file it accepted). isError is set whenever anything errored, so an agent can gate on it before trusting the payload.

Full parameter reference: [.ai-rulez/skills/poly-mcp/SKILL.md](.ai-rulez/skills/poly-mcp/SKILL.md).

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Performance

Release build, Apple Silicon, cold cache (--no-cache), best of three runs on an idle machine. poly lint --no-workspace and poly fmt --check over the whole repository, counting the files poly actually inspected. These are poly's own numbers — not a comparison against ruff, oxlint, biome or anything else; no such benchmark was run.

| Project | poly lint | Findings | Peak RSS | poly fmt --check | |---|---|---|---|---| | Django | 3,113 files in 0.82s | 66,839 | 0.21 GB | 5,539 files in 0.30s | | home-assistant | 25,443 files in 3.5s | 376,829 | 0.48 GB | 25,559 files in 1.2s | | Kubernetes | 21,657 files in 6.8s | 41,576 | 0.40 GB | 21,824 files in 12.9s | | prettier | 7,057 files in 1.9s | 19,373 | 0.40 GB | 7,450 files in 0.44s | | TypeScript | 32,606 files in 13.3s | 179,586 | 0.52 GB | 40,012 files in 4.0s |

Kubernetes is the one repository where formatting costs more than linting: its Go files go through gofmt, the one backend that is a subprocess rather than a linked-in crate, and ~20,000 process spawns dominate the run.

The blake3 cache and rayon parallelism (see [How It Works](#how-it-works)) are what keep repeat runs fast — Django re-lints in 0.71s warm against 0.82s cold: a cache hit skips the engine entirely, and everything else is split across cores.

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Documentation

A single poly.toml drives linting, formatting, git hooks, and commit-message policy; poly.local.toml layers local overrides on top, nested files cascade in a monorepo, and poly config show prints the effective merged result. Unknown keys, unknown sections and wrongly-typed values are reported as warnings, never silently ignored.

• Quickstart — install, first run, first config.
• Configuration — every key, rule selection, inline

suppression, monorepo cascading, shared and remote config.

• Hooks — poly hooks install, builtin hooks, staged isolation,

timeouts, concurrency, caching.

• CLI reference — every subcommand and flag, and the exit-code

contract.

• [Backends](https://goldzihe

…

Source & license

This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Goldziher
• Source: Goldziher/poly
• License: MIT
• Homepage: https://goldziher.github.io/poly

Install and usage instructions live in the source repository linked above.