clj-kondo – static analyzer and linter for Clojure

Clj-kondo performs static analysis on Clojure, ClojureScript and EDN. It informs you about potential errors while you are typing (without executing your program).

This linter is:

• compatible with .clj, .cljs, .cljc and .edn files.
• build tool and editor agnostic.
• a static code analyzer.
• compiled to native code using GraalVM.

This is free and open source software.

Key Features

Detects:

• inline def expressions.
• redundant do and let wrappings.
• arity errors:
  • within the same namespace and across namespaces.
  • of static Java method calls.
  • of local let and letfn binding calls.
  • of recursive calls (including recur).
  • conflicting arities in overloaded functions.
• unused private vars.
• private and deprecated var usage.
• required but unused namespaces.
• unsorted required namespaces.
• referred but unused vars.
• duplicate requires.
• unused function arguments and let bindings.
• marked as unused, but used arguments and let bindings (optional).
• unused imports.
• redefined vars.
• unresolved symbols, vars and namespaces.
• misplaced docstrings.
• duplicate map keys and set elements.
• duplicates and quoting in case test constants.
• missing map keys.
• invalid number of forms in binding vectors.
• missing assertions in clojure.test/deftest
• alias consistency.
• type checking.
• Datalog syntax checking.
• format string argument mismatches.
• shadowed vars.
• 2 argument usage of reduce (optional).

before your form hits the REPL.

It suggests several style guide recommendations, such as:

• rules from Stuart Sierra’s how to ns.
• use :else as the catch-all test expression in cond.
• use seq instead of (not (empty? ,,,)).
• don’t make your lines too long.

Website: github.com/clj-kondo/clj-kondo
Support:
Developer: Michiel Borkent
License: Eclipse Public License

clj-kondo is written in Clojure. Learn Clojure with our recommended free books and free tutorials.

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