Leiningen

Leiningen (lein) is Clojure's original build tool (from 2009) and still powers a large share of existing projects. It does everything in one tool: dependencies, REPL, tests, uberjars, and project templates.

project.clj

;; illustrative — project.clj
(defproject inventory "0.1.0-SNAPSHOT"
  :description "Inventory service"
  :url "https://example.com/inventory"
  :dependencies [[org.clojure/clojure "1.12.6"]
                 [org.clojure/data.json "2.5.2"]
                 [ring/ring-core "1.15.5"]]
  :main ^:skip-aot inventory.core
  :target-path "target/%s"
  :profiles {:dev {:dependencies [[org.clojure/test.check "1.1.3"]]}
             :uberjar {:aot :all
                       :jvm-opts ["-Dclojure.compiler.direct-linking=true"]}})

project.clj is itself Clojure code: defproject with a name, a version, and a map of options. :profiles add settings for development and for building the uberjar.

Everyday commands

lein new app inventory     # create a project from the "app" template
lein repl                  # start an nREPL server and a REPL client
lein run                   # run the :main namespace's -main
lein test                  # run clojure.test tests in test/
lein uberjar               # build target/uberjar/inventory-0.1.0-SNAPSHOT-standalone.jar
lein deps :tree            # show the dependency tree

deps.edn or Leiningen?

New projects increasingly use the CLI; you'll meet both. Editors (Calva, Cursive, CIDER) support both, and the language and libraries are the same either way.