cargo-arc

Generates a collapsible arc diagram of your Cargo workspace as SVG. You get a tree of your crates and their modules, connected by arcs that trace use dependencies between them.

Installation

cargo install cargo-arc

Requires a stable Rust toolchain.

Quick Start

# In any Cargo workspace:
cargo arc -o deps.svg

Open the generated SVG in a browser.

What You See

Your workspace shows up as a tree — crates with their modules nested inside. Arcs between nodes show where dependencies exist.

• Boxes — crates and modules, nested by hierarchy
• Arcs — dependencies between any two nodes
• Collapse a node to fold its children — individual dependencies merge into summary arcs
• Select a node or arc to highlight its relationships
• Cycles — circular dependencies are detected and highlighted

Features

• Cross-crate module dependencies — traces use dependencies across the whole workspace at module level
• Feature filtering — show only crates involved in a specific Cargo feature
• Interactive SVG — collapse, expand, and select directly in the browser
• External dependencies — visualize which external crates your modules depend on
• Volatility report — identifies frequently-changed modules based on git history

Feature Filtering

Show only the dependency subgraph for a specific Cargo feature:

# Show crates involved in the "web" feature (includes default deps)
cargo arc --features web -o web-deps.svg

# Exclude default deps — show ONLY the "web" feature graph
cargo arc --features web --no-default-features -o web-deps.svg

External Dependencies

Show which external crates your modules depend on:

# Direct external dependencies only
cargo arc --externals -o deps.svg

# Include transitive external dependencies
cargo arc --externals --transitive-deps -o deps.svg

External dependencies appear as separate nodes in the graph. The sidebar distinguishes direct from transitive dependencies with distinct styling.

Expand Level

Start with deeper modules pre-collapsed to keep large workspaces readable:

# Show only crates (everything collapsed)
cargo arc --expand-level 0 -o deps.svg

# Show crates and their direct modules
cargo arc --expand-level 1 -o deps.svg

Nodes beyond the given depth start collapsed. Click to expand interactively.

Volatility Report

Analyze which modules changed most frequently over the last months:

cargo arc --volatility

Useful for identifying hotspots before refactoring. The analysis period and thresholds are configurable (--volatility-months, --volatility-low, --volatility-high).

Similar Projects

• cargo tree — built-in textual dependency tree (crate-level)
• cargo-modules — module tree and dependency visualization
• cargo-depgraph — crate-level dependency graph as DOT with color-coded dependency kinds
• cargo-coupling — coupling analysis based on Khononov's framework

References

The arc diagram layout is inspired by Martin Wattenberg's Arc Diagrams: Visualizing Structure in Strings (IEEE InfoVis 2002).

Development

See docs/ARCHITECTURE.md for project structure and architecture decision records.

Requires Just as task runner.

just build
just test    # Rust + JS
just lint    # clippy + format check
just fmt

License

MIT OR Apache-2.0