Culler

Culler is a fast, high-confidence dead-code analyzer for Python projects.

It is built in Rust, distributed as a single command-line tool, and designed to find dead Python code without turning ordinary public APIs, exports, tests, or dynamic Python edges into noisy findings.

culler check .

_{Left: median wall-clock runtime, where lower is better. Right: F1 score, the balance between precision and recall, where higher is better.}

Benchmark: 15 realistic Python projects, 57,068 lines, 715 expected findings, and comparisons against Vulture and deadcode. Results are corpus-specific; the methodology and reproduction commands are below.

Highlights

• High-confidence findings by default. Culler reports the findings it can support strongly, and keeps review-confidence findings available separately.
• Whole-project reachability for applications. Production roots let Culler identify code that is unreachable from known entry points.
• Conservative library analysis. Exports, public surfaces, tests, and dynamic behavior are handled carefully to avoid noisy reports.
• Useful without heavy setup. Basic unused-code checks work with little or no configuration, and deeper reachability is enabled with pyproject.toml.
• Automation-friendly output. JSON output uses stable rule and diagnostic identifiers for editors, dashboards, CI, and benchmark tooling.

Installation

The recommended installation methods for the CLI are uv tool and pipx:

uv tool install culler

pipx install culler

You can also install it into an existing Python environment:

python -m pip install culler

The PyPI package installs the compiled culler binary. It does not expose a Python import API yet.

Quick Start

Run Culler on the current project:

culler check .

Emit machine-readable JSON:

culler check . --format json

Show review-confidence findings as well as high-confidence findings:

culler check . --show-review

Explain a specific candidate or finding:

culler explain <candidate-or-finding-id> .

Exit codes are intentionally small:

Code	Meaning
0	Analysis completed without default-visible findings.
1	Analysis completed and default-visible findings were reported.
2	Input, configuration, parse, or completeness error.

Configuration

Culler reads configuration from pyproject.toml.

[tool.culler]
src = "src"
mode = "auto"
target-python = "3.12"

For applications, declare production roots when you want reachability findings:

[tool.culler]
src = "src"
mode = "application"
root_coverage = "complete"
roots = ["my_app.cli:main"]

For libraries, Culler treats exported and externally visible surfaces more conservatively:

[tool.culler]
src = "src"
mode = "library"

Useful fields:

Field	Purpose
src	Source root or roots to analyze.
mode	auto, application, or library.
root_coverage	partial or complete when roots are known.
roots	Application entry points such as pkg.cli:main.
tests	Test paths when they are not discoverable conventionally.
target-python	Python syntax/semantic target, currently 3.10 through 3.15.
exclude	Glob patterns to exclude from analysis.
allow_partial	Permit partial analysis without escalating to exit code 2.

Output and Rules

Text output is optimized for local development and CI logs. JSON output is intended for editors, dashboards, benchmarks, and automation.

culler check . --format json

Rule IDs are stable machine-readable identifiers:

Rule	Finding
CULL001	Unreferenced function.
CULL002	Unreferenced class.
CULL003	Root-unreachable function.
CULL004	Root-unreachable class.
CULL005	Unused import binding.
CULL006	Unused local binding.
CULL007	Unreachable statement range.
CULL008	Unused private method.

Diagnostic IDs such as CULL_P0101 describe analysis, parsing, or configuration problems.

Benchmark Methodology

The benchmark compares Culler with Vulture and deadcode on one fixed corpus of artificial but realistic Python projects. The projects are artificial because precision and recall need ground truth; many real repositories contain little confirmed dead code, and exhaustive manual labeling is subjective. The corpus is designed to resemble code developers commonly inherit: services, libraries, CLIs, workers, pipelines, plugin systems, configuration packages, and utility-heavy AI-era codebases.

Scope	Value
Projects	15
Python files	374
Python LOC	57,068
Expected findings	715
Clean projects	2
Large or noisy projects	2

The expected findings live under benchmark/expected/ and use comparable categories: unused imports, unused locals, unreachable statements, unused functions, unused classes, and unused private methods.

Tool Scope

Tool	Why included
Culler	Subject under evaluation.
Vulture	Classic Python dead-code detector.
deadcode	Newer whole-codebase Python unused-code detector.

Ruff, Pylint, Pyflakes, Flake8, autoflake, pycln, and unimport are not included in the headline comparison. They overlap on some unused-import or unused-local checks, but they are linters or cleanup tools rather than direct whole-project dead-code analyzers.

Scoring

Every expected finding not matched by a tool is a false negative. Every parsed tool finding in a scoreable category that does not match an expected finding is a false positive, including findings in clean projects. Matching is deterministic by category, path, symbol name where relevant, and source span; duplicate reports count once as a true positive and then as false positives.

Culler's headline score uses high-confidence findings. The benchmark also reports a Culler high-plus-review aggregate, which includes review-confidence findings from the same Culler JSON run. It does not represent a separate timed CLI invocation.

Runtime

Runtime includes subprocess startup time. That reflects command-line user experience and avoids special-casing tools written in different languages. By default, each tool gets one warmup run and five measured runs per project; the report uses median wall time. Result JSON records command lines, tool versions, Python version, OS, CPU, memory, and the Culler commit.

Peak RSS is recorded where /usr/bin/time -l exposes it. If unavailable, the result uses null.

Running the Benchmark

Validate the corpus and expected files:

python3 benchmark/run.py --validate-only

Run the benchmark runner self-tests:

python3 benchmark/test_run.py

Build Culler and run the full benchmark:

cargo build --release
python3 benchmark/run.py \
  --culler target/release/culler \
  --tools culler,vulture,deadcode \
  --runs 5 \
  --results benchmark/results/latest.json

Generated reports are written under benchmark/results/ and ignored by default. Raw tool outputs are retained under benchmark/results/raw/.

Development

Prerequisites:

• Rust 1.82 or newer
• Python 3.10 or newer
• uv for packaging and benchmark helper commands

Core checks:

cargo fmt --all --check
cargo check
cargo clippy --all-targets --all-features -- -D warnings
cargo test
python3 benchmark/test_run.py
python3 benchmark/run.py --validate-only

Build the PyPI package locally:

uvx maturin build --release --out dist --sdist
uvx twine check dist/*

Status

Culler is pre-1.0 software. Rule IDs are intended to be stable, but CLI, configuration, and JSON output details may still evolve before 1.0.

Releases use reviewed PRs and changelog updates. See CONTRIBUTING.md for commit and release guidance.

License

Culler is released under the MIT License. See LICENSE.