Configuration

Clj-kondo can be configured in four ways, by providing:

• a config.edn file in the .clj-kondo directory (see project setup)
• a --config file argument from the command line
• a --config EDN argument from the command line (see examples below)
• a namespace local configuration using :clj-kondo/config metadata in the namespace form

Config takes precedence in the order of namespace, command line, .clj-kondo/config.edn. Note that not all linters are currently supported in namespace local configuration.

Look at the default configuration for all available options.

• Linters
• Output

Linters

Disable a linter

$ echo '(select-keys [:a])' | clj-kondo --lint -
<stdin>:1:1: error: wrong number of args (1) passed to clojure.core/select-keys
linting took 10ms, errors: 1, warnings: 0

$ echo '(select-keys [:a])' | clj-kondo --lint - --config '{:linters {:invalid-arity {:level :off}}}'
linting took 10ms, errors: 0, warnings: 0

Enable optional linters

Some linters are not enabled by default. Right now these linters are:

• :missing-docstring: warn when public var doesn't have a docstring.

You can enable these linters by setting the :level:

{:linters {:missing-docstring {:level :warning}}}

Disable all linters but one

You can accomplish this by using ^:replace metadata, which will override instead of merge with other configurations:

$ clj-kondo --lint corpus --config '^:replace {:linters {:redundant-let {:level :info}}}'
corpus/redundant_let.clj:4:3: info: redundant let
corpus/redundant_let.clj:8:3: info: redundant let
corpus/redundant_let.clj:12:3: info: redundant let

Lint a custom macro like a built-in macro

In the following code the my-defn macro is defined, but clj-kondo doesn't know how to interpret it:

(ns foo)

(defmacro my-defn [name args & body]
  `(defn ~name ~args
     (do (println "hello!")
       ~@body)))

(my-defn foo [x])

Hence (foo 1 2 3) will not lead to an invalid arity error. However, the syntax of my-defn is a subset of clojure.core/defn, so for detecting arity errors we might have just linted it like that. That is what the following configuration accomplishes:

{:lint-as {foo/my-defn clojure.core/defn}}

Exclude unresolved symbols from being reported

In the following code streams is a macro that assigns a special meaning to the symbol where, so it should not be reported as an unresolved symbol:

(ns foo
  (:require [riemann.streams [streams]]))

(def email (mailer {:host "mail.relay"
                    :from "riemann@example.com"}))
(streams
  (where (and (= (:service event) “my-service”)
              (= (:level event) “ERROR”))
    ,,,))

This is the config for it:

{:linters
  {:unresolved-symbol
    {:exclude [(riemann.streams/streams [where])]}}}

To exclude all symbols in calls to riemann.streams/streams write :exclude [(riemann.streams/streams)], without the vector.

To exclude a symbol from being reported as unresolved globally in your project, e.g. foo, you can use :exclude [foo].

Sometimes vars are introduced by executing macros, e.g. when using HugSQL's def-db-fns. You can suppress warnings about these vars by using declare. Example:

(ns hugsql-example
  (:require [hugsql.core :as hugsql]))

(declare select-things)

;; this will define a var #'select-things:
(hugsql/def-db-fns "select_things.sql")

(defn get-my-things [conn params]
  (select-things conn params))

Furthermore, the :lint-as option can help treating certain macros like built-in ones. This is in clj-kondo's own config:

:lint-as {me.raynes.conch/programs clojure.core/declare
          me.raynes.conch/let-programs clojure.core/let}

and helps preventing false positive unresolved symbols in this code:

(ns foo (:require [me.raynes.conch :refer [programs let-programs]]))

(programs rm mkdir echo mv)
(let-programs [clj-kondo "./clj-kondo"]
  ,,,)

Exclude arity linting inside a specific macro call

Some macros rewrite their arguments and therefore can cause false positive arity errors. Imagine the following silly macro:

(ns silly-macros)

(defmacro with-map [m [fn & args]]
  `(~fn ~m ~@args))

which you can call like:

(silly-macros/with-map {:a 1 :d 2} (select-keys [:a :b :c])) ;;=> {:a 1}

Normally a call to this macro will give an invalid arity error for (select-keys [:a :b :c]), but not when you use the following configuration:

{:linters {:invalid-arity {:skip-args [silly-macros/with-map]}}}

Exclude required but unused namespace from being reported

In the following code, the namespaces foo.specs and bar.specs are only loaded for the side effect of registering specs, so we don't like clj-kondo reporting those namespaces as required but unused.

(ns foo (:require [foo.specs] [bar.specs]))
(defn my-fn [x] x)

That can be done using this config:

{:linters {:unused-namespace {:exclude [foo.specs bar.specs]}}}

A regex is also supported:

{:linters {:unused-namespace {:exclude [".*\\.specs$"]}}}

This will exclude all namespaces ending with .specs.

Exclude unused referred vars from being reported.

Imagine you want to have taoensso.timbre/debug available in all of your namespaces. Even when you don't use it, you don't want to get a warning about it. That can be done as follows:

{:linters {:unused-referred-var {:exclude {taoensso.timbre [debug]}}}}

Exclude deprecated var usage from being reported

Say you have the following function:

(ns app.foo)
(defn foo {:deprecated "1.9.0"} [])

and you still want to be able to call it without getting a warning, for example in function in the same namespace which is also deprecated:

(defn bar {:deprecated "1.9.0"} []
  (foo))

or in test code:

(ns app.foo-test
  (:require
   [app.foo :refer [foo]]
   [clojure.test :refer [deftest is]]))

(deftest foo-test [] (is (nil? (foo))))

To achieve this, use this config:

{:linters
 {:deprecated-var
  {:exclude
   {app.foo/foo
    {:defs [app.foo/bar]
     :namespaces [app.foo-test]}}}}}

A regex is also permitted, e.g. to exclude all test namespaces:

{:linters {:deprecated-var {:exclude {app.foo/foo {:namespaces [".*-test$"]}}}}}

Exclude unused bindings from being reported

To exclude unused bindings from being reported, start their names with underscores: _x. To exclude warnings about key-destructured function arguments, use:

{:linters {:unused-binding {:exclude-destructured-keys-in-fn-args true}}}

Examples:

$ echo '(defn f [{:keys [:a :b :c]} d])' | clj-kondo --lint -
<stdin>:1:18: warning: unused binding a
<stdin>:1:21: warning: unused binding b
<stdin>:1:24: warning: unused binding c
<stdin>:1:29: warning: unused binding d
linting took 8ms, errors: 0, warnings: 4

$ echo '(defn f [{:keys [:a :b :c]} _d])' | clj-kondo --lint - --config \
  '{:linters {:unused-binding {:exclude-destructured-keys-in-fn-args true}}}'
linting took 8ms, errors: 0, warnings: 0

Exclude unused private vars from being reported

Example code:

(ns foo) (defn- f [])

Example config:

{:linters {:unused-private-var {:exclude [foo/f]}}}

Alias consistency

Sometimes it's desirable to have a consistent alias for certain namespaces in a project. E.g. in the below code it could be desirable if every alias for old.api was old-api:

(ns foo (:require [new.api :as api]))
(ns bar (:require [old.api :as old-api]))
(ns baz (:require [old.api :as api]))

This configuration:

{:linters {:consistent-alias {:aliases {old.api old-api}}}}

will give this warning:

Inconsistent alias. Expected old-api instead of api.

Output

Print results in JSON format

$ clj-kondo --lint corpus --config '{:output {:format :json}}' | jq '.findings[0]'
{
  "type": "invalid-arity",
  "filename": "corpus/nested_namespaced_maps.clj",
  "row": 9,
  "col": 1,
  "level": "error",
  "message": "wrong number of args (2) passed to nested-namespaced-maps/test-fn"
}

Printing in EDN format is also supported.

Include and exclude files from the output

$ clj-kondo --lint "$(clj -Spath)" --config '{:output {:include-files ["^clojure/test"]}}'
clojure/test.clj:496:6: warning: redundant let
clojure/test/tap.clj:86:5: warning: redundant do
linting took 3289ms, errors: 0, warnings: 2

$ clj-kondo --lint "$(clj -Spath)" --config '{:output {:include-files ["^clojure/test"] :exclude-files ["tap"]}}'
clojure/test.clj:496:6: warning: redundant let
linting took 3226ms, errors: 0, warnings: 1

Show progress bar while linting

$ clj-kondo --lint "$(clj -Spath)" --config '{:output {:progress true}}'
.................................................................................................................
cljs/tools/reader.cljs:527:9: warning: redundant do
(rest of the output omitted)

Output canonical file paths

The config '{:output {:canonical-paths true}}' will output canonical file paths (absolute file paths without ..). This also shows the full path of a jar file when you lint a classpath.

$ clj-kondo --lint corpus --config '{:output {:canonical-paths true}}'
/Users/borkdude/dev/clj-kondo/corpus/cljc/datascript.cljc:8:1: error: datascript.db/seqable? is called with 2 args but expects 1
(rest of the output omitted)

Example configurations

These are some example configurations used in real projects. Feel free to create a PR with yours too.

• clj-kondo
• rewrite-cljc