Cargo Machete

cargo-machete - Unused Dependency Detection

Detect and remove unused dependencies in Rust projects using cargo-machete.

When to Use This Skill

Context

• Cargo.toml: !find . -maxdepth 1 -name \'Cargo.toml\'
• Workspace: !grep -q '\[workspace\]' Cargo.toml
• cargo-machete installed: !cargo machete --version
• Machete config: !find . -maxdepth 1 -name \'.cargo-machete.toml\'
• Workspace members: !grep -A 20 '^\[workspace\]' Cargo.toml

Execution

Execute this unused dependency analysis:

Step 1: Verify installation

Check if cargo-machete is installed (see Context above). If not installed, install it:

cargo install cargo-machete

Step 2: Run dependency analysis

Run cargo-machete with metadata for detailed output:

# Single crate
cargo machete --with-metadata

# Workspace (if Context shows workspace)
cargo machete --workspace --with-metadata

Step 3: Evaluate results

Review the output and classify each finding:

Step 4: Apply fixes

For confirmed unused dependencies, auto-remove them:

cargo machete --fix

For false positives, add ignore annotations in Cargo.toml:

serde = "1.0"  # machete:ignore - used via derive macro

Or create .cargo-machete.toml for project-wide ignores:

[ignore]
dependencies = ["serde", "log"]

Step 5: Verify build

After removing dependencies, confirm everything still compiles:

cargo check --all-targets
cargo test --no-run

False Positive Handling

Comparison with cargo-udeps

Use cargo-machete for fast CI checks. Use cargo-udeps for thorough audits:

cargo +nightly udeps --workspace --all-features

Agentic Optimizations

Quick Reference

Troubleshooting

For CI integration patterns, configuration file examples, pre-commit setup, and Makefile integration, see REFERENCE.md.

cargo-machete Reference

Detailed configuration, CI integration, and workflow patterns for cargo-machete.

Installation

# Install cargo-machete
cargo install cargo-machete

# Verify installation
cargo machete --version

Output Examples

Basic Output

$ cargo machete
Found unused dependencies in Cargo.toml:
  serde_json (unused)
  log (unused in lib, used in build.rs)
  tokio (unused features: macros)

With Metadata

$ cargo machete --with-metadata
Project: my_app (bin)
  Unused dependencies:
    - serde_json (0.1.0)
      Declared in: Cargo.toml [dependencies]
      Not used in: src/main.rs

  Partially used:
    - tokio (1.35.0)
      Unused features: macros, fs
      Used features: runtime, net

Configuration File

Create .cargo-machete.toml in project root:

# .cargo-machete.toml

# Global ignores
[ignore]
dependencies = [
  "serde",      # Used via derive macro
  "log",        # Used in macro expansion
]

# Per-crate ignores
[ignore.my_lib]
dependencies = ["lazy_static"]

[ignore.my_bin]
dependencies = ["clap"]

# Workspace-wide settings
[workspace]
# Don't analyze these crates
exclude = ["internal_tools", "examples"]

Inline Cargo.toml Ignores

[dependencies]
serde = "1.0"  # machete:ignore - used via re-export
log = "0.4"    # machete:ignore - used in macro expansion

Workspace Configuration

# Check all workspace members
cargo machete --workspace

# Check specific workspace members
cargo machete -p crate1 -p crate2

# Exclude specific members
cargo machete --workspace --exclude integration_tests

CI Integration

GitHub Actions with cargo-machete

name: Dependency Check

on: [push, pull_request]

jobs:
  unused-deps:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: dtolnay/rust-toolchain@stable

      - name: Install cargo-machete
        uses: taiki-e/install-action@v2
        with:
          tool: cargo-machete

      - name: Check for unused dependencies
        run: cargo machete --with-metadata

Official GitHub Action

name: Dependency Check

on: [push, pull_request]

jobs:
  unused-deps:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Check unused dependencies
        uses: bnjbvr/cargo-machete@main

GitHub Actions with cargo-udeps (Nightly)

name: Dependency Check

on: [push, pull_request]

jobs:
  unused-deps:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: dtolnay/rust-toolchain@nightly

      - uses: Swatinem/rust-cache@v2

      - name: Install cargo-udeps
        uses: taiki-e/install-action@v2
        with:
          tool: cargo-udeps

      - name: Check for unused dependencies
        run: cargo +nightly udeps --workspace --all-features

cargo-udeps Installation and Usage

# Install nightly and cargo-udeps
rustup toolchain install nightly
cargo +nightly install cargo-udeps

# Run analysis (requires nightly)
cargo +nightly udeps

# With specific features
cargo +nightly udeps --all-features

# For workspace
cargo +nightly udeps --workspace

Pre-commit Integration

# .pre-commit-config.yaml
repos:
  - repo: local
    hooks:
      - id: cargo-machete
        name: Check for unused dependencies
        entry: cargo machete
        language: system
        pass_filenames: false
        files: Cargo.toml$

Makefile Integration

# Makefile
.PHONY: deps-check deps-clean

deps-check:
	@echo "Checking for unused dependencies..."
	@cargo machete --with-metadata

deps-clean:
	@echo "Removing unused dependencies..."
	@cargo machete --fix
	@echo "Running cargo check..."
	@cargo check --all-targets

CI Script

#!/usr/bin/env bash
# scripts/check-deps.sh
set -euo pipefail

echo "Running cargo-machete..."
if ! cargo machete --with-metadata; then
  echo "Unused dependencies detected!"
  echo "Run 'cargo machete --fix' to remove them."
  exit 1
fi

echo "No unused dependencies found."

Combined Dependency Audit

# Full dependency audit
cargo machete                 # Check unused
cargo outdated                # Check outdated
cargo audit                   # Check security
cargo deny check licenses     # Check licenses

References

• cargo-machete repository
• cargo-udeps repository
• Official GitHub Action
• Rust dependency management best practices