• Credo's schema for pre-release names changes: There is now a . after the rc like in many other Elixir projects.

  • Add support for explaining checks (in addition to issues), i.e.

    $ mix credo explain Credo.Check.Design.AliasUsage
  • Add support for tags on checks

    Checks can now declare tags via the __using__ macro, i.e.

    defmodule MyCheck do
      use Credo.Check, tags: [:foo]
      def run(source_file, params) do

    Tags can be used via the CLI switch --checks-with[out]-tag:

    # Only run checks tagged `:foo` during analysis
    $ mix credo --checks-with-tag foo
    # Exclude all checks tagged `:foo` from analysis
    $ mix credo --checks-without-tag foo
  • Add validation of check params in config

    If a param is not found, Credo checks for mispellings and suggests corrections:

    $ mix credo
    ** (config) Credo.Check.Design.AliasUsage: unknown param `fi_called_more_often_than`. Did you mean `if_called_more_often_than`?
  • Add auto-generated check docs

  • Add new documentation on Hex with extra guides and CHANGELOG




  • Enable Credo.Check.Readability.UnnecessaryAliasExpansion check by default
  • Fix bugs when removing heredocs and charlists from sources
  • Fix false positive on TrailingWhiteSpace
  • Add ignore: [:fun1, :fun2] param to all UnusedOperation* checks; to ignore unused Enum.reduce/3 operations, use

    {Credo.Check.Warning.UnusedEnumOperation, [ignore: [:reduce]]},

New switch to re-enable disabled checks

Use --enable-disabled-checks [pattern] to re-enable checks that were disabled in the config using {CheckModule, false}. This comes in handy when using checks on a case-by-case basis

As with other check-related switches, pattern is a comma-delimted list of patterns:

$ mix credo info --enable-disabled-checks Credo.Check.Readability.Specs,Credo.Check.Refactor.DoubleBooleanNegation

Of course, we can have the same effect by choosing the pattern less explicitly:

$ mix credo info --enable-disabled-checks specs,double

New API for custom checks

This deprecates the mandatory use of @explanation and @default_params module attributes for checks.

Before v1.3 you had to define module attributes named @explanation and @default_params before calling use Credo.Check.

Now you can pass :explanations (plural) and :param_defaults options directly to use Credo.Check.

defmodule MyCheck do
  use Credo.Check,
    category: :warning,
    base_priority: :high,
    param_defaults: [param1: 42, param2: "offline"],
    explanations: [
      check: "...",
      params: [
        param1: "Your favorite number",
        param2: "Online/Offline mode"

  def run(source_file, params) do

Please note that these options are also just a convenience to implement the functions specified by the Credo.Check behaviour. You can alternatively implement the respective functions yourself:

defmodule MyCheck do
  use Credo.Check

  def category, do: :warning

  def base_priority, do: :high

  def explanations do
      check: "...",
      params: [
        param1: "Your favorite number",
        param2: "Online/Offline mode"

  def param_defaults, do: [param1: 42, param2: "offline"]

  def run(source_file, params) do

New checks


  • Fix performance bottleneck in Credo.Service.ETSTableHelper


  • Fix token interpretation of Floats



  • Commands can now have their own pipelines, so that plugins can extend them.
  • Add pipelines to SuggestCommand and ListCommand
  • Credo.Plugin.append_task/4 and Credo.Plugin.prepend_task/4 let you append/prepend tasks to Command's pipelines.
  • Validate options given to use Credo.Check
  • Fix TrailingWhiteSpace check on Windows
  • Fix MultiAlias to work with submodule expansion
  • Fix UnusedVariableNames bug
  • Fix Heredocs.replace_with_spaces/5 bug
  • Fix InterpolationHelper.replace_interpolations/2 bug
  • Fix crash in AliasAs check when MODULE is aliased
  • Fix speed pitfall in
  • New config option: parse_timeout
  • Improved default settings for umbrella apps

New checks


  • Add JSON output to categories and explain commands
  • Include number of executed checks in summary
  • Fix wrong trigger in SinglePipe


  • Fix name parsing bug in UnusedVariableNames
  • Fix bug when redefining operators in FunctionNames
  • Fix false positive in Specs


  • Improve warning message about skipped checks
  • Fix false positive in FunctionNames
  • Fix typespec in IssueMeta
  • Add AliasAs check to list of optional checks


  • Fix bug in Heredocs regarding indentation
  • Fix bug in FunctionNames when using unquote/1 in guards
  • Fix bug in FunctionNames when defining sigil_ functions for uppercase sigils


  • Fix incompatibilities between Elixir 1.9, Credo.Code.Token and Credo.Code.InterpolationHelper
  • Fix error in Heredocs with certain UTF-8 chars
  • New param for ParenthesesOnZeroArityDefs: use [parens: true] to force presence of parentheses on zero arity defs


  • Credo now requires Elixir 1.5 and Erlang/OTP 19
  • Fix false negative in DuplicatedCode
  • PipeChainStart has been made opt-in

Plugin Support

Credo now supports plugins that run alongside Credo's own analysis. While Credo provided the ability to write custom checks since v0.4.0, users can now access the complete toolset of Credo to create their own commands, require compilation, run external tools and still include the results in Credo's standard report.

Please refer to Credo's README as well as the Credo Demo Plugin for further information on how to get started.

New checks

  • Credo.Check.Refactor.WithClauses


  • Fix bug due to commented-out heredocs
  • Fix variable explanation for VariableRebinding check
  • Add MultiAlias check to experimental checks


  • Ignore heredocs in RedundantBlankLines
  • Fix bug in StringSigils
  • Minor refactorings


  • Fix bug in Name.full/1
  • Fix bug in UI.truncate/2
  • Disable LazyLogging for Elixir >= 1.7
  • Add UnnecessaryAliasExpansion check to experimental checks


  • Fix false positive in MapInto
  • Disable MapInto for Elixir 1.8 and higher
  • Ensure issues are sorted by filename, line number and column number
  • Warn about ineffective check filter patterns
  • Add ModuleDependencies check to experimental checks


  • Compilation warnings for Elixir 1.8
  • Fix StringSigils to not crash with strings containing non-UTF8 characters


  • Improve documentation
  • Add error handling for malformed config files
  • Write all warnings to :stderr
  • Fix false positive for charlists in PipeChainStart
  • Remove deprecated --one-line switch
  • Deactivate checks DuplicatedCode and DoubleBooleanNegation by default


These changes concern people writing their own checks for Credo.

  • Credo.Check.CodeHelper was removed. Please use the corresponding functions inside the Credo.Code namespace.


  • Fix bug in AliasOrder


  • Fixed "unnecessary atom quotes" compiler warning during analysis
  • Handle timeouts when reading source files
  • Ignore function calls for OperationOnSameValues
  • Do not treat |> as an operator in SpaceAroundOperators
  • Fix AliasOrder bug for multi alias statements
  • Fix multiple false positives for SpaceAroundOperators
  • ... and lots of important little fixes to issue messages, docs and the like!


  • Switch poison for jason
  • Add command-line switch to load a custom configuration file (--config-file)
  • Add a debug report in HTML format when running Credo using --debug
  • Add node_modules/ to default file excludes
  • Add :ignore_urls param for MaxLineLength
  • Report violation for not as well as ! in Refactor.NegatedConditionWithElse
  • Fix false positive on LargeNumbers
  • Fix NegatedConditionWithElse for not/2 as well
  • Disable PreferUnquotedAtoms for Elixir >= 1.7.0

New checks

  • Credo.Check.Refactor.MapInto


  • Fix bug in Scope
  • Fix false positive in MatchInConditionTest
  • Fix false positive in UnusedEnumOperation
  • Fix custom tasks by resolving config before validating it
  • Add text support to --min-priority CLI switch (you can now set it to low/normal/high)

New checks

  • Credo.Check.Readability.AliasOrder


  • Add :ignore_comments param to LongQuoteBlocks
  • Fix false positive in UnusedPathOperation


  • Fix false positive in SpaceAroundOperators
  • Fix false positive in UnusedEnumOperation


  • Add JSON support
  • Ensure compatibility with Elixir 1.6
  • Format codebase using Elixir 1.6 Formatter
  • Rework internals in preparation of 1.0 release
  • Credo now requires Elixir 1.4
  • Include test directory in default config
  • Add excluded_argument_types to PipeChainStart
  • Emit warnings for non-existing checks, which are referenced in config
  • Improve VariableNames
  • ModuleDoc now raises an issue for empty strings in @moduledoc tags
  • Fix bug on ModuleNames
  • Fix false positive in VariableRebinding
  • Fix false positive in SpaceAroundOperators
  • Fix false positive on BoolOperationOnSameValues
  • Fix false positive on SpaceAfterCommas
  • Fix false positive on MaxLineLength
  • Fix false positive in ParenthesesInCondition
  • Remove NameRedeclarationBy* checks
  • Remove support for @lint attributes


  • Maintenance release


  • Fix false positive in ParenthesesInCondition
  • Fix Code.to_tokens/1 for Elixir 1.6
  • Fix documentation for several checks

New checks

  • Credo.Check.Warning.ExpensiveEmptyEnumCheck


  • Fix false positive for LargeNumbers
  • Fix SpaceAroundOperators for @type module attributes
  • Ignore def arguments and specs for OperationOnSameValues
  • Fix crash in ParenthesesOnZeroArityDefs for variables named defp
  • Fix false positives for TagHelper


  • Fix false positive in ModuleAttributeNames
  • Fix false positives in unused return checks
  • Fix underlining in "list" action
  • Fix CLI argument parsing for mix credo.gen.check
  • Fix loading of custom checks
  • Prevent error when run against empty umbrella projects
  • Prevent output for tests


  • Fix false positive in SpaceAfterCommas
  • Fix false positive in SpaceAroundOperators
  • Fix bug with extracting explain command args
  • Allow anonymous functions to be piped as raw values


  • Speed up scope counting in CLI summary


  • Remove CheckForUpdates for good
  • Fix RaiseInsideRescue for implicit try


  • Do not run CheckForUpdates on CI systems and in editor integrations


  • Refactor all consistency checks, providing a nice speed improvement (thx @little-bobby-tables)
  • Improve Elixir 1.5 compatibility


  • Fix misleading issue message for LongQuoteBlocks


  • Load source files in parallel
  • Improve high memory consumption
  • Fix comment handling of Charlists, Sigils and Strings
  • LazyLogging now only checks for debug calls by default
  • Add --mute-exit-status CLI switch, which mutes Credo's exit status (this will be used for integration tests as it means that any non-zero exit status results from a runtime error of Credo)
  • Add default param values to mix explain output
  • TagTODO and TagFIXME now also report tags from doc-related module attributes (@doc, @moduledoc, @shortdoc)
  • Fix false positives for TrailingWhiteSpace
  • Fix compiler warnings for Sigils


These changes concern people writing their own checks for Credo.

Config Comments replace @lint attributes

@lint attributes are deprecated and will be removed in Credo 0.9.0 because they are causing a compiler warning in Elixir >= 1.4.

Users of Credo can now disable individual lines or files for all or just specific checks.

For now, config comments let you exclude individual files completely

# credo:disable-for-this-file
defmodule SomeApp.ThirdPartyCode do

or deactivate specific lines:

def my_fun do
  # credo:disable-for-next-line
  IO.inspect :this_is_actually_okay

or add the check module to exclude just that one check:

def my_fun do
  # credo:disable-for-next-line Credo.Check.Warning.IoInspect
  IO.inspect :this_is_actually_okay

or use a Regex to be more flexible which checks to exclude:

def my_fun do
  # credo:disable-for-next-line /IoInspect/
  IO.inspect :this_is_actually_okay

Here's a list with the syntax options:

  • # credo:disable-for-this-file - to disable for the entire file
  • # credo:disable-for-next-line - to disable for the next line
  • # credo:disable-for-previous-line - to disable for the previous line
  • # credo:disable-for-lines:<count> - to disable for the given number of lines (negative for previous lines)

New checks

  • Credo.Check.Refactor.LongQuoteBlocks


  • Fix false positives in SpacesAroundOperators
  • Fix --all CLI switch
  • Always enforce strict mode for <filename>:<line_no>
  • Improve docs on checks
  • Disable MultiAliasImportRequireUse by default

Disabled checks

  • Credo.Check.Consistency.MultiAliasImportRequireUse


  • Fix filename annotation when using --read-from-stdin
  • Fix filename handling on Windows
  • Fix consistency checks triggered by contents of sigils
  • Fix consistency checks triggered by contents of charlists

New check

  • Credo.Check.Warning.LazyLogging


  • Fix @lint attribute deprecation hint
  • Fix filename handling bug for Windows
  • Fix flycheck formatting
  • Add param to ignore strings/heredocs in TrailingWhiteSpace

New check

  • Credo.Check.Readability.SpaceAfterCommas


  • Fix --config_nameCLI switch
  • Fix UI.wrap_at/2 for Unicode strings
  • Fix false positive for ModuleNames


  • Added deprecation hint about @lint attributes
  • Fixed file inclusion/exclusion bug
  • Fixed false positives in SpaceAroundOperators
  • Deprecated NameRedeclarationBy* checks
  • Fixed false positives in PipeChainStart
  • Changed AppendSingleItem's priority and make it opt-in
  • Renamed NoParenthesesWhenZeroArity to ParenthesesOnZeroArityDefs
  • Fixed a bug in ParenthesesOnZeroArityDefs

Added/deprecated checks

  • Credo.Check.Warning.MapGetUnsafePass
  • Credo.Check.Refactor.AppendSingleItem
  • Credo.Check.Readability.Semicolons

Switched some checks to opt-in by default

  • Credo.Check.Readability.Specs
  • Credo.Check.Refactor.ABCSize
  • Credo.Check.Refactor.VariableRebinding
  • Credo.Check.Warning.MapGetUnsafePass
  • Credo.Check.Warning.NameRedeclarationByAssignment
  • Credo.Check.Warning.NameRedeclarationByCase
  • Credo.Check.Warning.NameRedeclarationByDef
  • Credo.Check.Warning.NameRedeclarationByFn


  • Fixed false positives for StringSigils in heredocs
  • Fixed a bug in SourceFile.column


  • Do not warn about ParenthesesInCondition in one-line if call
  • Add --no-strict CLI switch
  • Fixed exit status for mix credo list
  • Fixed exclusion of checks set to low priority

New Checks

  • consistency/multi_alias_import_require_use
  • readability/no_parentheses_when_zero_arity
  • readability/redundant_blank_lines
  • readability/single_pipe
  • readability/specs
  • readability/string_sigils
  • refactor/double_boolean_negation
  • refactor/variable_rebinding


  • Fix crash in CheckForUpdates


  • Add ability to specify strict in .credo.exs config file
  • Add no_case? to variable name checks
  • Add utility method
  • Fix bug in NameRedeclarationByDef
  • Fix bug in LargeNumbers


  • Use API to retrieve update information for Credo


  • See below


  • Fix compiler error due to usage of undocumented Hex APIs (sorry)


  • Prevent crashing when parsing non-UTF-8 source files
  • Fix yet another issue with finding sources
  • Fix false positives for PipeChainStart
  • Fix false positives for AbcSize
  • Remove dead code
  • Update deps


  • Prevent ModuleDoc from checking nested modules for ignored modules
  • Fix issue with ParenthesesInCondition
  • Fix issue with PipChainStart
  • Fix issue with reading from stdin
  • Log errors to stderr


  • Fix compatibility issues with Elixir < 1.2
  • Fix yet another issue with finding sources


  • Fix another issue with finding sources


  • Fix issues with finding sources
  • Don't enforce @moduledoc requirement for Mixfile or Test modules


  • Add exclude_functions option to PipeChainStart
  • No longer report issues in case of ambiguous aliases in AliasUsage
  • Fix false positives for LargeNumbers in Elixir >= 1.3.2 (again)
  • Lots of refactorings


  • Ignore module attributes like @spec in AliasUsage
  • Improve source file loading


  • Add ignore_specs option to MaxLineLength
  • Fix false positives for LargeNumbers in Elixir >= 1.3.2
  • Fix compiler warnings in preparation for Elixir v1.4


  • Warnings about redeclaring names of Kernel or local functions now only consider function of arity zero.
  • Warnings for operations with constant result now ignore division by 1
  • Better explanation how to configure checks in explain output


  • New check: readability/parentheses_in_condition


  • Fix compatibility issues in Credo.CLI.Command.GenCheck for Elixir < 1.2


  • Fix outdated comments regarding .credo.exs in README
  • Fix name generator including "Lib." prefix for custom checks


  • Maintenance release because I apparently don't understand how merging works :sweat:


Custom check support

  • Adds support for custom checks in your projects.

    Using two new mix commands mix credo.gen.config and mix credo.gen.check you can generate the boilerplate to include custom checks in your projects.

BREAKING CHANGE: Checks listed in .credo.exs

  • Prior to v0.4.0, .credo.exs contained the full list of checks specific to your project
  • Starting with v0.4.0 the check list in credo.exs will be merged with the standard check list, with your definitions overwriting the defaults
  • PRO: you can customize individual tasks to your liking and still benefit from additional standard checks with each new release
  • CON: this means checks have to be disabled explicitly in .credo.exs

New Checks

  • readability/large_numbers
  • warning/bool_operation_on_same_values
  • warning/unused_file_operation
  • warning/unused_path_operation
  • warning/unused_regex_operation

Minor Improvements

  • Ready for Elixir 1.3
  • Checks for new Credo versions automatically, like Hex does (can be disabled)
  • Umbrella apps work out of the box now
  • DuplicatedCode can now ignore macro calls
  • ModuleDoc now ignores modules declaring exceptions
  • ModuleDoc now allows modules to be ignored based on their name
  • MatchInCondition now allows "simple" wildcard assignments in conditionals
  • Checks analysing all files in the codebase sequentially (consistency checks) are now run in parallel
  • If --only is given, all issues are shown (mix credo --only MaxLineLength previously yielded no results, since all issues needed --strict to actually be displayed)


  • Fix false positives for NameRedeclarationByDef.
  • Fix false positives for UnusedEnumOperation.


  • Fix false positives for SpaceInParentheses.
  • Fix false positive for SpaceAroundOperators.


  • Fix a bug with checks on function names when declaring a variable with the name def, defp or defmacro.



  • Fix a bug in AliasUsage.


  • Fix false positives for AliasUsage.


  • Fix false positive for SpaceAroundOperators.


  • Fix false positives for SpaceAroundOperators and PipeChainStart.
  • Add option to read from STDIN for better editor integration


  • Remove superfluous call to IO.inspect.
  • Update deps requirements to make HexFaktor happy.


  • Fix false positives for SpaceAroundOperators in binary pattern matches.
  • Fix a bug when supplying a single file via the CLI.


  • Fix false positives for SpaceAroundOperators and SpaceInParentheses.


  • mix do credo, <something-else> was broken and never ran <something-else>, even if credo succeeded (exited with exit status 0). Now it runs <something-else> as long as credo succeeds.


  • Fix compiler warnings
  • Improve copywriting for consistency checks (thx @vdaniuk)


Per-function lint support

  • Adds support for @lint attributes used to configure linting for specific functions.

    For now, this lets you exclude functions completely

    @lint false
    def my_fun do

    or deactivate specific checks with the same syntax used in the config file:

    @lint {Credo.Check.Design.TagTODO, false}
    def my_fun do

    or use a Regex instead of the check module to exclude multiple checks at once:

    @lint {~r/Refactor/, false}
    def my_fun do

    Finally, you can supply multiple tuples as a list and combine the above:

    @lint [{Credo.Check.Design.TagTODO, false}, {~r/Refactor/, false}]
    def my_fun do

New Checks

  • consistency/space_around_operators
  • consistency/space_in_parentheses

Minor Improvements

  • Add --format CLI switch
  • Include experimental Flycheck support via --format=flycheck
  • Deprecate --one-line CLI switch, use --format=oneline instead
  • Add convenience alias --ignore for --ignore-checks
  • Fix colors for terminals with light backgrounds (thx @lucasmazza)


  • Fix false positives for UnusedEnumOperation checks (thx @kbaird)


  • Fix error occuring when a project has exactly one defexception module
  • Change the tag for Refactoring Opportunities from "[R]" to "[F]" (thx @rranelli)


  • Remove unused alias to avoid warning during compilation


  • Improves docs and UI wording (thx @crack and @jessejanderson)


  • Adds a missing word to the output of the categories command (thx @bakkdoor)


  • Fixes a problem with CaseTrivialMatches crashing


Error Status

Credo now fails with an exit status != 0 if it shows any issues. This will enable usage of Credo inside CI systems/build chains.

The exit status of each check is customizable and exit statuses of all encountered checks are collected, uniqued and summed:

|> Enum.uniq
|> Enum.reduce(0, &(&1+&2))

This way you can reason about the encountered issues right from the exit status.

Default values for the checks are based on their category:

consistency:  1
design:       2
readability:  4
refactor:     8
warning:     16

So an exit status of 12 tells you that you have only Readability Issues and Refactoring Opportunities, but e.g. no Warnings.

New Checks

  • readability/module_doc
  • refactor/case_trivial_matches
  • refactor/cond_statements
  • refactor/function_arity
  • refactor/match_in_condition
  • refactor/pipe_chain_start
  • warning/operation_with_constant_result
  • warning/unused_enum_operation
  • warning/unused_keyword_operation
  • warning/unused_list_operation
  • warning/unused_tuple_operation

Minor Improvements

  • There are two new aliases for command line switches:

    • you can use --only as alias for --checks
    • you can use --strict as alias for --all-priorities
  • mix credo --only <checkname> will always display a full list of results (you no longer need to specify --all separately)
  • mix credo explain <file:line_number> now also explains the available configuration parameters for the issue/check
  • The ExceptionNames check no longer fails if only a single exception module is found (#22).


  • Apply many fixes in anticipation of Elixir v1.2 (thx @c-rack)
  • Improve docs
  • Wrap long issue descriptions in suggest command


  • Add missing -A alias for --all-priorities
  • Improve wording in the CLI a bit


  • Add apps/ to default directories


  • Bugfix to NameRedeclarationBy\* checks
  • Sources.exclude had a bug when excluding directories


  • Rename CLI switch --pedantic to --all-priorities (alias is -A)
  • Fix a bug in SourceFile.column (#7)
  • Improve README section about basic usage, commands and issues

0.1.1 - 0.1.5

Multiple Hex releases due to the fact that I apparently don't understand how deps compilation works :sweat:


Initial release