cargo-machete - Unused Dependency Detection

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

When to Use This Skill

Use this skill when...	Use X instead when...
Auditing for unused dependencies	Checking for outdated deps -- use `cargo outdated`
Cleaning up Cargo.toml	Auditing security vulnerabilities -- use `cargo audit`
Optimizing build times by removing bloat	Checking license compliance -- use `cargo deny`
Verifying deps in CI	Need nightly-accurate analysis -- use `cargo +nightly udeps`

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

Execute this unused dependency analysis:

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

cargo install cargo-machete

Run cargo-machete with metadata for detailed output:

# Single crate
cargo machete --with-metadata

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

Review the output and classify each finding:

Finding	Action
Genuinely unused dependency	Remove with `--fix` or manually
Proc-macro dependency (e.g., serde derive)	Add `machete:ignore` comment
Build.rs-only dependency	Move to `[build-dependencies]`
Re-exported dependency	Add `machete:ignore` comment with explanation

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"]

After removing dependencies, confirm everything still compiles:

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

Scenario	Solution
Proc-macro deps (e.g., serde derive)	`machete:ignore` comment
Build.rs-only deps	Move to `[build-dependencies]`
Re-exported deps	`machete:ignore` comment with explanation
Example/bench-only deps	Verify in `[dev-dependencies]`

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

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

Context	Command
Quick check	`cargo machete`
Detailed check	`cargo machete --with-metadata`
Workspace check	`cargo machete --workspace --with-metadata`
Auto-fix	`cargo machete --fix`
Verify after fix	`cargo check --all-targets`
Accurate check (nightly)	`cargo +nightly udeps --workspace`

Flag	Description
`--with-metadata`	Show detailed output with versions and locations
`--fix`	Auto-remove unused dependencies from Cargo.toml
`--workspace`	Check all workspace members
`-p <crate>`	Check specific workspace member
`--exclude <crate>`	Exclude specific workspace member

Problem	Solution
Proc macro flagged as unused	Add `machete:ignore` comment in Cargo.toml
Build.rs dep flagged	Move to `[build-dependencies]`
Re-exported dep flagged	Add `machete:ignore` with explanation
Need more accuracy	Use `cargo +nightly udeps`

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