Choose Between Leiningen and deps.edn

Choosing between Leiningen and deps.edn is less about declaring a winner and more about respecting the project you are in. A Java engineer should first ask: “Which tool owns this repository’s classpath, REPL, tests, and packaging?”

Start With Repository Evidence

Do not start by asking which tool is newer. Start by identifying the tool that the project actually runs.

Compare the Workflows

The Clojure CLI is intentionally smaller. Leiningen is intentionally more project-task oriented. Both can be professional tools.

Decision Flow

    flowchart TD
	    A["Existing repository?"] -->|Yes| B["Follow README and CI"]
	    A -->|No| C["Need built-in app tasks and uberjar now?"]
	    B --> D["Use the tool already owning classpath/tests/package"]
	    C -->|Yes| E["Leiningen is a simple first choice"]
	    C -->|No| F["deps.edn keeps the project lightweight"]
	    F --> G["Add tools.build only when packaging is needed"]
	    E --> H["Keep project.clj small and use lein repl"]

The diagram is deliberately conservative: tool choice should reduce friction, not create identity work.

When Leiningen Is a Good Choice

Choose Leiningen when:

• you inherited a project.clj codebase
• your team already documents lein test, lein repl, or lein uberjar
• you want a quick application scaffold
• you need a plugin already used by the project
• simple built-in packaging is useful early

Leiningen is especially approachable for Java engineers who expect named build tasks and one project file.

When deps.edn Is a Good Choice

Choose deps.edn when:

• you want explicit classpath roots and aliases
• the project is small or library-like
• you prefer ordinary Clojure namespaces for tasks
• the team already uses Clojure CLI tooling
• you expect to add tools.build only when packaging becomes necessary

deps.edn is not “less serious” because it is small. It is a different model: compose classpaths and invoke functions deliberately.

Migration Costs

Migrating from one tool to another is not only a file conversion.

Migrate only when the benefit is concrete: simpler CI, fewer plugins, clearer classpath, better tool-task separation, or alignment with the team’s current standards.

A Practical Rule for Java Engineers

Use this default:

The wrong choice is usually not “Leiningen” or “deps.edn.” The wrong choice is mixing both without clear ownership.

Key Takeaways

• Repository evidence beats tool preference.
• Leiningen provides built-in project tasks and a familiar automation model.
• deps.edn provides explicit classpath composition and composable CLI modes.
• Migration has real costs in CI, editor setup, packaging, and docs.
• Be fluent enough in both tools to contribute before advocating a change.

Quiz: Choose Tools