Reach builds a program dependence graph for Elixir, Erlang, Gleam, JavaScript, and TypeScript projects and turns it into command-line reports and interactive HTML visualizations.
Use Reach when you want to answer questions such as:
- What are the riskiest functions to change?
- Which modules are tightly coupled?
- Where does a value, tainted input, or return shape flow?
- Which functions mix unrelated side effects?
- Which OTP processes hide state, message, or coupling risks?
Reach 2.x is organized around five canonical Mix tasks:
| Command | Purpose |
|---|---|
mix reach.map | Project-level map: modules, coupling, hotspots, effects, depth, and data-flow summaries |
mix reach.inspect TARGET | Target-local explanations: dependencies, impact, graph, context, data, candidates, and why paths |
mix reach.trace | Data-flow, taint, and slicing workflows |
mix reach.check | CI/release checks: architecture, changed-code risk, dead code, smells, and candidates |
mix reach.otp | OTP/process analysis: behaviours, state machines, supervision, concurrency, and coupling |
For machine consumers, use --format json. Canonical commands emit pure JSON envelopes with stable command names.
Projects can extend smell checks with local Reach.Smell.Check modules. See the custom smells guide for examples.
Design goals
Reach reports evidence. It does not auto-edit your code. Refactoring candidates are advisory and include graph/effect/architecture evidence so humans can decide what is safe.