Clojure Build Tools

If you come from Java, it is tempting to ask “which one is the official build tool?” In Clojure, the more useful question is: “which toolchain does this project use, and how do I get a REPL and tests running quickly?”

You will see two main workflows:

• tools.deps / Clojure CLI: configuration in deps.edn, flexible aliases, and strong alignment with the JVM classpath model.
• Leiningen: configuration in project.clj, a long history in the ecosystem, and a plugin-based workflow many older projects still use.

Practical Guidance

• Prefer learning to run what exists before migrating anything.
• For new projects, many teams default to tools.deps, but legacy Lein projects are still common and productive.
• Treat both like Maven vs Gradle: you do not need a holy war, you need fluency.

This section helps you recognize the files, commands, and mental models so you can join a codebase and be effective.

In this section

• Understand Leiningen Projects
  Learn how Leiningen uses project.clj, named tasks, profiles, plugins, the project REPL, and uberjar packaging so you can work confidently in existing Clojure repositories.
• Create a Leiningen Project
  Generate a Leiningen application, read its project.clj and namespace layout, run the app, run tests, and start the project REPL without confusing the scaffold with architecture.
• Understand deps.edn and the Clojure CLI
  Understand how deps.edn, clj, clojure, aliases, classpath roots, main invocations, exec functions, and tools aliases fit together in modern Clojure CLI projects.
• Create a deps.edn Project
  Create a small Clojure CLI project by hand, wire source and test paths, add run and test aliases, and verify the project from the shell before adding more tooling.
• Choose Between Leiningen and deps.edn
  Compare Leiningen and deps.edn by repository signals, team workflow, REPL expectations, testing, packaging, and migration cost so Java engineers choose tools pragmatically.