konform

Multi-rule Python linter and language server — fast, configurable, and CI-ready.

Work in progress. konform is under active development. Rules, configuration keys, CLI flags, and the LSP surface may change at any time, including in backwards-incompatible ways, until a 1.0 release.

Rules

KIS001 — Module-only imports

Checks that every from X import Y only imports a sub-module, not an object (function, class, or constant), following the Google Python Style Guide §2.2.

# Bad — KIS001: `join` is a function, not a module
from os.path import join

# Good
import os.path
from os import path       # `path` is a module

This rule is sometimes fixable: konform rewrites the import automatically when it's safe to do so. It leaves the violation for you to fix by hand when the new import's name is already bound elsewhere in the file -- either as a local variable, or by a different import that would then overlap with it (two from X import Y statements silently bound to the same name but pointing at different modules).

KIS002 — Unnecessary import alias

Flags from X import Y as Z when the alias Z buys nothing -- Y isn't bound to anything else in the module, so the alias only adds a layer of indirection.

# Bad — KIS002: `bar_baz` isn't needed, nothing else is named `baz`
from foo.bar import baz as bar_baz

# Good
from foo.bar import baz

The alias is left alone when it's actually doing something: renaming away a collision with a local name or another import, a leading-underscore "don't re-export this" marker, a self-alias (import x as x, which is Ruff's PLC0414 territory), or a relative import (from . import x as y, which has no stable module identity to key a collision check on). Plain import X as Z statements are out of scope too -- dropping the alias there changes what gets bound, unlike from X import Y as Z.

This rule is sometimes fixable: konform drops the alias and renames every use of it back to the original name. It leaves the violation for you to fix by hand when the alias is shadowed somewhere, or bound to more than one import in the file.

The fix is marked unsafe -- konform can't rule out other, dynamic references to the alias by name, so it's only applied with --unsafe-fixes (see Usage below).

KPT — User-defined pattern rules

Load regex patterns from konform_patterns.toml (auto-discovered next to pyproject.toml) or inline in pyproject.toml:

[[tool.konform.KPT.rules]]
id      = "KPT001"
message = "Use the project logger instead of bare print()."
pattern = '^\s*print\s*\('
files   = ["src/**/*.py"]
level   = "warning"

Installation

pip install konform

Wheels ship a pre-compiled Rust binary — no Rust installation needed at runtime.

Usage

# Lint all Python files under src/
konform check src/

# Lint and apply auto-fixes in one pass
konform check --fix src/

# Also apply fixes marked unsafe (e.g. KIS002)
konform check --fix --unsafe-fixes src/

# Apply fixes only (no lint report)
konform check --fix src/

# Show a unified diff of what format would change
konform check --diff src/

# Output violations as JSON (e.g. for tooling)
konform check --output-format json src/

# Suppress hints and summary (violations only)
konform check -q src/

# No output — just exit 1 on violations
konform check -s src/

# List all rules
konform rule --list

# Explain a rule
konform rule --explain KIS001

# Clear the local cache
konform clean

When some reported violations are fixable only via --unsafe-fixes (e.g. KIS002), the summary breaks safe and unsafe-only counts out separately, and the suggested fix command is adjusted accordingly.

Configuration

Add a [tool.konform] section to pyproject.toml (or a standalone konform.toml):

[tool.konform]
cache-dir = ".konform_cache"
workers   = 0         # 0 = os.cpu_count()
src       = [".", "src"]   # search roots for KIS001's module-existence probe;
                            # see "Module search roots" below.

[tool.konform.lint]
select = []        # [] = all rules; prefix match: "KIS" = all KIS* rules
ignore = []
level  = "error"   # "warning" | "error"

# ── KIS001 — import style ──────────────────────────────────────────────────
[tool.konform.lint.module-only-imports]
exceptions = [
    "__future__", "typing", "typing_extensions", "collections.abc",
    "mycompany.compat",
]
level = "error"
unresolved-level = "warning"   # "warning" (default) | "error" | "off"
                                # Used when a package isn't installed in this
                                # environment, so KIS001 can't tell whether the
                                # imported name is a module or not.

# ── KIS002 — unnecessary import alias ──────────────────────────────────────
[tool.konform.lint.unnecessary-import-alias]
level = "warning"

# ── KPT001 — user-defined patterns ─────────────────────────────────────────
[tool.konform.lint.user-defined-patterns]
level = "warning"
# Optional: load patterns from an external file instead of inline rules.
# rules_file = "konform_patterns.toml"

[[tool.konform.lint.user-defined-patterns.rules]]
id      = "KPT001"
message = "Use the project logger instead of bare print()."
pattern = '^\s*print\s*\('
files   = ["src/**/*.py"]
level   = "warning"

# Sub-rules are attached to this rule entry. This inline form makes the
# parent/child relation explicit and avoids table-order confusion.
sub_rules = [
  {
    pattern = ['print\(.*password', 'print\(.*secret'],
    message = "Never print credentials.",
    help = "Use redaction helpers before logging.",
  },
]

Each rule's settings live in its own table, keyed by a stable config name (shown by konform rule --list) rather than by rule code — so renaming a rule code (with noqa-aliases covering old suppression comments) never forces you to also rewrite your config.

When using [[tool.konform.lint.user-defined-patterns.rules.sub_rules]], TOML binds each sub-rule to the most recently declared [[tool.konform.lint.user-defined-patterns.rules]] entry.

Pattern files

Patterns can also live in a standalone konform_patterns.toml placed next to pyproject.toml. konform auto-discovers it (no config key needed):

# konform_patterns.toml
[[rules]]
id      = "KPT002"
message = "Remove breakpoint() — debugging artefact."
pattern = '^\s*breakpoint\s*\(\s*\)'
level   = "error"

Module search roots

KIS001 needs to know whether an imported name is a real module (import os.path) or just an attribute of one (from os.path import join). It answers this by searching the filesystem, starting from your Python environment's sys.path plus a configurable set of extra roots -- this matters for local packages that aren't installed (e.g. a src/ layout, or code laid out some other way).

The extra roots are resolved the same way as Ruff's src setting, including its precedence:

1. [tool.konform] src = [...], if set.
2. Otherwise, [tool.ruff] src = [...], if your project already configures Ruff for a non-standard layout.
3. Otherwise, the default [".", "src"] (covers both flat and src layouts out of the box).

Each entry is resolved relative to the directory containing pyproject.toml / konform.toml. For example, if your package lives under lib/:

[tool.konform]
src = ["lib"]

Suppressing violations

from os.path import join   # noqa: KIS001   ← exact rule
from os.path import join   # noqa: KIS       ← whole category
from os.path import join   # noqa             ← everything on this line

Aliasing noqa codes

When a rule code changes (e.g. a rule is renamed, or a project migrates from another linter's codes), old # noqa comments would otherwise stop working. Define aliases in your config so they keep suppressing the renamed/canonical rule:

# pyproject.toml
[tool.konform.lint.noqa-aliases]
IS001 = "KIS001"
IS    = "KIS"

from os.path import join   # noqa: IS001   ← suppresses KIS001 via alias

Upgrading from an older config format

When konform's config shape changes (as it did in 0.3.0, moving rule selection/settings under [tool.konform.lint]), it auto-migrates an outdated pyproject.toml / konform.toml the first time you run any konform command: the file is rewritten in place (comments and other [tool.*] sections are preserved) and a summary of what changed is printed to stderr. No action is needed beyond re-running konform once.

Language Server (LSP)

konform ships a built-in LSP server that shares the same rule engine as the CLI — no second process, no stale results.

konform server   # starts the LSP over stdin/stdout

Code actions mirror the CLI's fix-safety split: a per-violation quickfix is offered for every fixable diagnostic (including unsafe ones, e.g. KIS002 — editing a single open document is an explicit, reviewable action), plus two document-wide "fix all" actions: Fix all auto-fixable problems (safe fixes only, source.fixAll.konform) and Fix all problems (including unsafe fixes) (source.fixAll.konform.unsafe), the latter only offered when it would change something beyond the safe-only pass.

Neovim (nvim-lspconfig)

vim.api.nvim_create_autocmd("FileType", {
  pattern = "python",
  callback = function()
    vim.lsp.start({
      name = "konform",
      cmd  = { "konform", "server" },
      root_dir = vim.fs.dirname(
        vim.fs.find({ "pyproject.toml", "konform.toml" }, { upward = true })[1]
      ),
    })
  end,
})

VS Code (settings.json)

Add via the generic None ls or any client that supports a custom LSP command:

{
  "nls.server": {
    "command": ["konform", "server"]
  }
}

Zed

Install the zed-konform extension (see extensions/zed-extension/README.md) and Zed will auto-install the konform binary for you — no manual setup required. To override the binary path or pass extra arguments, set:

{
  "lsp": {
    "konform": {
      "binary": {
        "path": "konform",
        "arguments": ["server"]
      }
    }
  }
}

Development

# Compile the Rust binary and install it in the dev venv (required before tests)
hatch run develop

# Run tests with coverage
hatch test -c

# Build release wheels for all platforms
hatch run maturin:build-all

CLI reference

konform check  [OPTIONS] <PATHS>…    Lint files (default subcommand)
konform check --fix-only [OPTIONS] <PATHS>…  Apply all auto-fixes in-place, exit 0
konform server                       Start the LSP server (stdin/stdout)
konform rule   --list                List all rules
konform rule   --explain <CODE>      Show full rule documentation
konform clean  [--config PATH]       Delete the cache directory
konform version                      Print konform's version

Global options (available on all subcommands):
  --color auto|always|never          Colour output control
  --isolated                         Ignore all config files
  -v / --verbose                     Extra output
  -q / --quiet                       Violations only (no summary/hints)
  -s / --silent                      No output; exit code only

Acknowledgements

konform exists because Ruff doesn't (yet) cover rules like KIS001/KIS002 — konform was built to fill that gap, and Ruff's design was a direct inspiration for how konform is configured, how it reports violations, and how it resolves src search roots.

konform is also built on top of several excellent open-source projects, especially:

• ruff_python_parser, ruff_python_ast, and ruff_text_size — Ruff's own Python parser and AST, published standalone on crates.io.

Thanks to all the maintainers of all used open-source projects.