smellcheck 0.2.5

Python code smell detector -- 82 refactoring patterns, 55 AST checks, zero dependencies

smellcheck

Python Code Smell Detector & Refactoring Guide
82 refactoring patterns · 55 automated AST checks · zero dependencies

smellcheck is a Python code smell detector and refactoring catalog. It works as a pip-installable CLI, GitHub Action, pre-commit hook, or Agent Skills plugin for AI coding assistants.

No dependencies. Pure Python stdlib (ast, pathlib, json). Runs anywhere Python 3.10+ runs.

Installation

pip

pip install smellcheck

smellcheck src/
smellcheck myfile.py --format json
smellcheck src/ --min-severity warning --fail-on warning

GitHub Action

- uses: cheickmec/smellcheck@v1
  with:
    paths: 'src/'
    fail-on: 'error'       # exit 1 on error-level findings (default)
    min-severity: 'info'   # display all findings (default)
    format: 'github'       # GitHub annotations (default)

pre-commit

repos:
  - repo: https://github.com/cheickmec/smellcheck
    rev: v0.2.0
    hooks:
      - id: smellcheck
        args: ['--fail-on', 'warning']

Agent Skills (Claude Code, Codex CLI, Cursor, Copilot, Roo Code, Gemini CLI)

Any tool supporting the Agent Skills standard can install directly:

# Claude Code
/plugin marketplace add cheickmec/smellcheck
/plugin install python-refactoring@smellcheck

# OpenAI Codex CLI
$skill-installer install cheickmec/smellcheck

# Cursor
# Import from GitHub URL in skills settings

# Or install from a local clone
git clone https://github.com/cheickmec/smellcheck.git
# Point your tool to plugins/python-refactoring/skills/python-refactoring/

Manual setup for other tools

For tools without Agent Skills support (Aider, Windsurf, Continue.dev, Amazon Q), copy the relevant files into your project's instruction directory:

• Copy SKILL.md content into your tool's instruction file (.cursorrules, CONVENTIONS.md, .windsurf/rules/, etc.)
• Install with pip install smellcheck and run the smellcheck CLI

Usage

# Scan a directory
smellcheck src/

# Scan multiple files
smellcheck file1.py file2.py

# JSON output
smellcheck src/ --format json

# GitHub Actions annotations
smellcheck src/ --format github

# Filter by severity
smellcheck src/ --min-severity warning

# Control exit code
smellcheck src/ --fail-on warning   # exit 1 on warning or error
smellcheck src/ --fail-on info      # exit 1 on any finding

# Run only specific checks
smellcheck src/ --select 001,057,CC

# Skip specific checks
smellcheck src/ --ignore 003,006

# Module execution
python -m smellcheck src/

# Generate a baseline of current findings
smellcheck src/ --generate-baseline > .smellcheck-baseline.json

# Only report findings not in the baseline
smellcheck src/ --baseline .smellcheck-baseline.json

Configuration

smellcheck reads [tool.smellcheck] from the nearest pyproject.toml:

[tool.smellcheck]
select = ["001", "002", "057"]       # only run these checks (default: all)
ignore = ["003", "006"]              # skip these checks
per-file-ignores = {"tests/*" = ["002", "034"]}  # per-path overrides
fail-on = "warning"                  # override default fail-on
format = "text"                      # override default format
baseline = ".smellcheck-baseline.json"  # suppress known findings

CLI flags override config values.

Inline Suppression

Add # noqa: SC057 to a line to suppress pattern #057 on that line:

def foo(x=[]):  # noqa: SC057
    return x

Use # noqa (no codes) to suppress all findings on that line. Multiple codes: # noqa: SC003,SC006

Baseline

For large codebases, you can adopt smellcheck incrementally using a baseline file. The baseline records fingerprints of existing findings so only new issues are reported.

# 1. Generate a baseline from the current state
smellcheck src/ --generate-baseline > .smellcheck-baseline.json

# 2. Run with the baseline — only new findings are reported
smellcheck src/ --baseline .smellcheck-baseline.json

# 3. Or set it in pyproject.toml so every run uses it automatically

Fingerprints are resilient to line-number changes — renaming or moving code around won't break the baseline. When you fix a baselined smell, its entry is silently ignored.

--generate-baseline and --baseline are mutually exclusive.

Features

• 55 automated smell checks -- per-file AST analysis, cross-file dependency analysis, and OO metrics
• 82 refactoring patterns -- numbered catalog with before/after examples, trade-offs, and severity levels
• Zero dependencies -- stdlib-only, runs on any Python 3.10+ installation
• Multiple output formats -- text (terminal), JSON (machine-readable), GitHub annotations (CI)
• Configurable -- pyproject.toml config, inline suppression, CLI overrides
• Baseline support -- adopt incrementally by suppressing existing findings and only failing on new ones
• Four distribution channels -- pip, GitHub Action, pre-commit, Agent Skills

Detected Patterns

Every rule has a unified SC code (e.g. SC701) and a legacy pattern ref (e.g. 057). Both forms work in --select, --ignore, and # noqa comments.

Per-File (40 checks)

SC Code	#	Pattern	Severity
SC101	001	Setters (half-built objects)	warning
SC102	008	UPPER_CASE without Final	info
SC103	009	Unprotected public attributes	info
SC104	016	Half-built objects (init assigns None)	warning
SC105	017	Boolean flag parameters	info
SC106	024	Global mutable state	info
SC107	028	Sequential IDs	info
SC201	002	Long functions (>20 lines)	warning
SC202	006	Generic names (data, result, tmp)	info
SC203	026	input() in business logic	warning
SC204	029	Functions returning None or list	info
SC205	033	Excessive decorators (>3)	info
SC206	034	Too many parameters (>5)	warning
SC207	041	CQS violation (query + modify)	info
SC208	064	Unused function parameters	warning
SC209	066	Long lambda (>60 chars)	info
SC210	CC	Cyclomatic complexity (>10)	warning
SC301	007	Extract class (too many methods)	info
SC302	014	isinstance chains	warning
SC303	018	Singleton pattern	warning
SC304	061	Dataclass candidate	info
SC305	062	Sequential tuple indexing	info
SC306	069	Lazy class (<2 methods)	info
SC307	070	Temporary fields	warning
SC401	021	Dead code after return	warning
SC402	039	Deep nesting (>4 levels)	warning
SC403	040	Loop + append pattern	info
SC404	042	Complex boolean expressions	warning
SC405	055	Boolean control flag in loop	info
SC406	067	Complex comprehension (>2 generators)	info
SC407	068	Missing default else branch	info
SC501	051	Error codes instead of exceptions	warning
SC502	054	Law of Demeter violation	info
SC601	003	Magic numbers	info
SC602	004	Bare except / unused exception variable	error
SC603	036	String concatenation for multiline	info
SC604	063	contextlib candidate	info
SC605	065	Empty catch block	warning
SC701	057	Mutable default arguments	error
SC702	058	open() without context manager	warning

Cross-File (10 checks)

SC Code	#	Pattern	Description
SC211	FE	Feature envy	Function accesses external attributes more than own
SC308	DIT	Deep inheritance	Inheritance depth >4
SC309	WHI	Wide hierarchy	>5 direct subclasses
SC503	CYC	Cyclic imports	DFS cycle detection
SC504	GOD	God modules	>500 lines or >30 top-level definitions
SC505	SHO	Shotgun surgery	Function called from >5 different files
SC506	INT	Inappropriate intimacy	>3 bidirectional class references between files
SC507	SPG	Speculative generality	Abstract class with no concrete subclasses
SC508	UDE	Unstable dependency	Stable module depends on unstable module
SC606	013	Duplicate functions	AST-normalized hashing across files

OO Metrics (5 checks)

SC Code	#	Metric	Threshold
SC801	LCOM	Lack of Cohesion of Methods	>0.8
SC802	CBO	Coupling Between Objects	>8
SC803	FIO	Excessive Fan-Out	>15
SC804	RFC	Response for a Class	>20
SC805	MID	Middle Man (delegation ratio)	>50%

Refactoring Reference Files

Each pattern includes a description, before/after code examples, and trade-offs:

File	Patterns
state.md	Immutability, setters, attributes (001, 008, 009, 016, 017, 030)
functions.md	Extraction, naming, parameters, CQS (002, 010, 020, 026, 027, 034, 037, 041, 050, 052, 064, 066)
types.md	Classes, reification, polymorphism, nulls (007, 012, 014, 015, 019, 022, 023, 029, 038, 044, 048, 069, 070, DIT, WHI)
control.md	Guards, pipelines, conditionals, phases (039-043, 046, 047, 049, 053, 055, 056, 067, 068)
architecture.md	DI, singletons, exceptions, delegates (018, 024, 028, 035, 045, 051, 054, SHO, INT, SPG, UDE)
hygiene.md	Constants, dead code, comments, style (003, 004, 011, 013, 021, 025, 031-033, 036, 065)
idioms.md	Context managers, generators, unpacking (057-063)
metrics.md	OO metrics: cohesion, coupling, fan-out, response, delegation (LCOM, CBO, FIO, RFC, MID)

Compatibility

Tool	Install Method	Status
pip	pip install smellcheck	Native support
GitHub Actions	uses: cheickmec/smellcheck@v1	Native support
pre-commit	.pre-commit-config.yaml	Native support
Claude Code	/plugin install	Native support
OpenAI Codex CLI	$skill-installer	Native support
Cursor	GitHub import / .cursor/skills/	Native support
GitHub Copilot	MCP gallery	Native support
Roo Code	.roo/ directory	Native support
Gemini CLI	Agent Skills	Native support
Windsurf	Copy to .windsurf/rules/	Manual
Aider	--read CONVENTIONS.md	Manual
Continue.dev	.continue/rules/	Manual
Amazon Q	.amazonq/rules/	Manual

How It Compares

Feature	smellcheck	PyExamine	SMART-Dal	Pyscent
Automated detections	55	49	31	11
Refactoring guidance	82 patterns	None	None	None
Dependencies	0 (stdlib)	pylint, radon	DesigniteJava	pylint, radon, cohesion
Python-specific idioms	Yes	No	No	No
Cross-file analysis	Yes	Limited	Yes	No
OO metrics	5	19	0	1
Distribution channels	4 (pip, GHA, pre-commit, Agent Skills)	1	1	1

Contributing

Contributions welcome. The core detector is src/smellcheck/detector.py -- add new checks by extending the SmellDetector AST visitor class and adding a cross-file analysis function if needed.

# Development setup
git clone https://github.com/cheickmec/smellcheck.git
cd smellcheck
pip install -e .
pip install pytest

# Run tests
pytest tests/ -v

# Self-check
smellcheck src/smellcheck/

License

MIT