Overview

Credo is a static code analysis tool for Elixir focused on code quality and consistency.

Configuration File

.credo.exs

%{
  configs: [
    %{
      name: "default",
      strict: true,
      color: true,
      files: %{
        included: ["lib/", "src/", "test/", "web/", "apps/*/lib/", "apps/*/test/"],
        excluded: [~r"/_build/", ~r"/deps/", ~r"/node_modules/"]
      },
      plugins: [],
      requires: [],
      parse_timeout: 5000,
      checks: %{
        enabled: [
          # Consistency checks
          {Credo.Check.Consistency.ExceptionNames, []},
          {Credo.Check.Consistency.LineEndings, []},
          {Credo.Check.Consistency.ParameterPatternMatching, []},
          {Credo.Check.Consistency.SpaceAroundOperators, []},
          {Credo.Check.Consistency.SpaceInParentheses, []},
          {Credo.Check.Consistency.TabsOrSpaces, []},

          # Design checks
          {Credo.Check.Design.AliasUsage, [priority: :low, if_nested_deeper_than: 2]},
          {Credo.Check.Design.TagFIXME, []},
          {Credo.Check.Design.TagTODO, [exit_status: 0]},

          # Readability checks
          {Credo.Check.Readability.AliasOrder, []},
          {Credo.Check.Readability.FunctionNames, []},
          {Credo.Check.Readability.LargeNumbers, []},
          {Credo.Check.Readability.MaxLineLength, [priority: :low, max_length: 120]},
          {Credo.Check.Readability.ModuleAttributeNames, []},
          {Credo.Check.Readability.ModuleDoc, []},
          {Credo.Check.Readability.ModuleNames, []},
          {Credo.Check.Readability.ParenthesesInCondition, []},
          {Credo.Check.Readability.ParenthesesOnZeroArityDefs, []},
          {Credo.Check.Readability.PipeIntoAnonymousFunctions, []},
          {Credo.Check.Readability.PredicateFunctionNames, []},
          {Credo.Check.Readability.PreferImplicitTry, []},
          {Credo.Check.Readability.RedundantBlankLines, []},
          {Credo.Check.Readability.Semicolons, []},
          {Credo.Check.Readability.SpaceAfterCommas, []},
          {Credo.Check.Readability.StringSigils, []},
          {Credo.Check.Readability.TrailingBlankLine, []},
          {Credo.Check.Readability.TrailingWhiteSpace, []},
          {Credo.Check.Readability.UnnecessaryAliasExpansion, []},
          {Credo.Check.Readability.VariableNames, []},
          {Credo.Check.Readability.WithSingleClause, []},

          # Refactoring opportunities
          {Credo.Check.Refactor.Apply, []},
          {Credo.Check.Refactor.CondStatements, []},
          {Credo.Check.Refactor.CyclomaticComplexity, [max_complexity: 12]},
          {Credo.Check.Refactor.FunctionArity, [max_arity: 8]},
          {Credo.Check.Refactor.LongQuoteBlocks, []},
          {Credo.Check.Refactor.MatchInCondition, []},
          {Credo.Check.Refactor.MapJoin, []},
          {Credo.Check.Refactor.NegatedConditionsInUnless, []},
          {Credo.Check.Refactor.NegatedConditionsWithElse, []},
          {Credo.Check.Refactor.Nesting, [max_nesting: 3]},
          {Credo.Check.Refactor.UnlessWithElse, []},
          {Credo.Check.Refactor.WithClauses, []},

          # Warnings
          {Credo.Check.Warning.ApplicationConfigInModuleAttribute, []},
          {Credo.Check.Warning.BoolOperationOnSameValues, []},
          {Credo.Check.Warning.ExpensiveEmptyEnumCheck, []},
          {Credo.Check.Warning.IExPry, []},
          {Credo.Check.Warning.IoInspect, []},
          {Credo.Check.Warning.OperationOnSameValues, []},
          {Credo.Check.Warning.OperationWithConstantResult, []},
          {Credo.Check.Warning.RaiseInsideRescue, []},
          {Credo.Check.Warning.SpecWithStruct, []},
          {Credo.Check.Warning.UnusedEnumOperation, []},
          {Credo.Check.Warning.UnusedFileOperation, []},
          {Credo.Check.Warning.UnusedKeywordOperation, []},
          {Credo.Check.Warning.UnusedListOperation, []},
          {Credo.Check.Warning.UnusedPathOperation, []},
          {Credo.Check.Warning.UnusedRegexOperation, []},
          {Credo.Check.Warning.UnusedStringOperation, []},
          {Credo.Check.Warning.UnusedTupleOperation, []},
          {Credo.Check.Warning.UnsafeExec, []}
        ],
        disabled: [
          # Controversial and experimental checks
          {Credo.Check.Consistency.MultiAliasImportRequireUse, []},
          {Credo.Check.Consistency.UnusedVariableNames, []},
          {Credo.Check.Design.DuplicatedCode, []},
          {Credo.Check.Design.SkipTestWithoutComment, []},
          {Credo.Check.Readability.AliasAs, []},
          {Credo.Check.Readability.BlockPipe, []},
          {Credo.Check.Readability.ImplTrue, []},
          {Credo.Check.Readability.MultiAlias, []},
          {Credo.Check.Readability.NestedFunctionCalls, []},
          {Credo.Check.Readability.OneArityFunctionInPipe, []},
          {Credo.Check.Readability.OnePipePerLine, []},
          {Credo.Check.Readability.SeparateAliasRequire, []},
          {Credo.Check.Readability.SingleFunctionToBlockPipe, []},
          {Credo.Check.Readability.SinglePipe, []},
          {Credo.Check.Readability.Specs, []},
          {Credo.Check.Readability.StrictModuleLayout, []},
          {Credo.Check.Readability.WithCustomTaggedTuple, []},
          {Credo.Check.Refactor.ABCSize, []},
          {Credo.Check.Refactor.AppendSingleItem, []},
          {Credo.Check.Refactor.DoubleBooleanNegation, []},
          {Credo.Check.Refactor.FilterReject, []},
          {Credo.Check.Refactor.IoPuts, []},
          {Credo.Check.Refactor.MapMap, []},
          {Credo.Check.Refactor.ModuleDependencies, []},
          {Credo.Check.Refactor.NegatedIsNil, []},
          {Credo.Check.Refactor.PipeChainStart, []},
          {Credo.Check.Refactor.RejectFilter, []},
          {Credo.Check.Refactor.VariableRebinding, []},
          {Credo.Check.Warning.LazyLogging, []},
          {Credo.Check.Warning.LeakyEnvironment, []},
          {Credo.Check.Warning.MapGetUnsafePass, []},
          {Credo.Check.Warning.MixEnv, []},
          {Credo.Check.Warning.UnsafeToAtom, []}
        ]
      }
    }
  ]
}

Multiple Configurations

%{
  configs: [
    %{
      name: "default",
      # Default strict config
    },
    %{
      name: "legacy",
      files: %{
        included: ["lib/legacy/"]
      },
      checks: %{
        disabled: [
          {Credo.Check.Readability.ModuleDoc, []}
        ]
      }
    }
  ]
}

Command Line Options

# Use specific config
mix credo --config-name legacy

# Strict mode
mix credo --strict

# Show all issues
mix credo --all

# Only specific categories
mix credo --only readability,refactor

Priority Levels

• :higher - Critical issues
• :high - Important issues
• :normal - Default priority
• :low - Minor issues
• :ignore - Completely disabled