Why polylint

polylint replaces a per-language stack — a linter and formatter per ecosystem, each with its own config, report format and install step, glued together by a hook framework — with one binary and one poly.toml.

Compared with what you may use now

If you use…	What changes	Trade-off
ruff, oxlint, biome, mago, … individually	The same engines — ruff, oxc, biome and mago are linked as libraries, not reimplemented — behind one config, one report format, one cache and one exit-code contract. No per-ecosystem toolchain for the built-in engines.	polylint pins each engine to its own release; a new upstream version arrives with a polylint release.
pre-commit or lefthook	poly hooks runs from poly.toml, checks a snapshot of the staged index rather than the worktree, and needs no Python environment. poly migrate converts .pre-commit-config.yaml and lefthook.yml.	Hooks from arbitrary repositories run as commands polylint shells out to, as they would under those frameworks.
MegaLinter or Super-Linter	No Docker image: a native binary fast enough for local runs and git hooks as well as CI, with a content-hash cache and per-line findings parsed from each tool’s report.	They wrap more linters; polylint covers the long tail with tree-sitter formatting and an opt-in catalog with file-level verdicts.
dprint	polylint lints as well as formats.	dprint’s plugin model is open to third-party formatters; polylint’s engine set is curated.

What it guarantees

• One contract. Exit 0 is clean, 1 is findings, 2 is “verified less than it claims” — a file an engine failed on, a skip budget exceeded, a missing component.
• Coverage is counted. A file nothing could check is named with its reason, and --deny-skips makes that a failure, so a run that checked nothing cannot pass as clean.
• Pinned engines. Components are signed, verified against a lock embedded in the binary, and versioned with polylint. What varies by machine — host tools and recipe tools — is listed in Toolchains, runtimes and recipes.
• Agents use the same surface. poly mcp exposes lint, format, config and component tools with structured output, so an agent does not parse terminal text.

When it is not the right tool

• You need a specific linter polylint has no engine or recipe for, with per-line findings. A catalog tool runs it, but reports one verdict per file.
• Your CI image cannot run a native binary or reach a component mirror, and you cannot use the bundled Linux musl build.