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Regexp based customizable linter
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Goodcheck logo

Goodcheck - Regexp based customizable linter

Are you reviewing a pull request if the change contains deprecated API calls? Do you want to post a comment to ask the developer if a method call satisfies some condition to use that without causing an issue? What if a misspelling like Github for GitHub can be found automatically?

Give Goodcheck a try to do them instead of you! 🎉

Goodcheck is a customizable linter. You can define pairs of patterns and messages. It checks your program and when it detects a piece of text matching with the defined patterns, it prints your message which tells your teammates why it should be revised and how. Some part of code reviewing process can be automated. Everything you have to do is to define the rules, pairs of patterns and messages, and nothing will bother you. 😆


$ gem install goodcheck

Or you can use bundler!

If you would not like to install Goodcheck to system (e.g. you would not like to install Ruby 2.4 or higher), you can use a docker image. See below.


$ goodcheck init
$ vim goodcheck.yml
$ goodcheck check

The init command generates template of goodcheck.yml configuration file for you. Edit the config file to define patterns you want to check. Then run check command, and it will print matched texts.


An example of configuration is like the following:

  - id: com.example.github
    pattern: Github
    message: |
      GitHub is GitHub, not Github

      You may misspelling the name of the service!
      - When you mean a service different from GitHub
      - When GitHub is renamed
      - app/views/**/*.html.slim
      - config/locales/**/*.yaml
      - <a>Signup via GitHub</a>
      - <a>Signup via Github</a>

The rule hash contains the following keys.

  • id: a string to identify rules (required)
  • pattern: a pattern or a sequence of patterns (required)
  • message: a string to tell writers why the code piece should be revised (required)
  • justification: a sequence of strings to tell writers when a exception can be allowed (optional)
  • glob: a glob or a sequence of globs (optional)
  • pass: a string, or a sequence of strings, which does not match given pattern (optional)
  • fail: a string, or a sequence of strings, which does match given pattern (optional)


A pattern can be a literal pattern, regexp pattern, token pattern, or a string. When a string is given, it is interpreted as a literal pattern with case_sensitive: true.

literal pattern

literal pattern allows you to construct a regexp which matches exactly to the literal string.

id: com.sample.GitHub
  literal: Github
  case_sensitive: true
message: Write GitHub, not Github

All regexp meta characters included in the literal value will be escaped. case_sensitive is an optional key and the default is true.

regexp pattern

regexp pattern allows you to write a regexp with meta chars.

id: com.sample.digits
  regexp: \d{4,}
  case_sensitive: false
  multiline: false
message: Insert delimiters when writing large numbers
  - When you are not writing numbers, including phone numbers, zip code, ...

It accepts two optional attributes, case_sensitive and multiline. The default values of case_sensitive and multiline are true and false respectively.

The regexp will be passed to Regexp.compile. The precise definition of regular expression can be found in the documentation for Ruby.

token pattern

token pattern compiles to a tokenized regexp.

  token: "<blink"
  case_sensitive: false
message: Stop using <blink> tag
glob: "**/*.html"
  - If Lynx is the major target of the web site

It tries to tokenize the input and generates a regexp which matches sequence of tokens. The tokenization is heuristic and may not work well for your programming language. In that case, try using regexp pattern.

The generated regexp of <blink is <\s*blink\b/m. It matches with <blink /> and < BLINK>, but does not match with

It accepts one optional attribute, case_sensitive. The default value of case_sensitive is true. Note that the generated regexp is in multiline mode.


A glob can be a string, or a hash.

  pattern: "legacy/**/*.rb"
  encoding: EUC-JP

The hash can have an optional encoding attribute. You can specify encoding of the file by the names defined for ruby. The list of all available encoding names can be found by $ ruby -e "puts Encoding.name_list". The default value is UTF-8.

If you write a string as a glob, the string value can be the pattern of the glob, without encoding attribute.

If you omit glob attribute in a rule, the rule will be applied to all files given to goodcheck.

Importing rules

goodcheck.yml can have optional import attribute.

rules: []
  - /usr/share/goodcheck/rules.yml
  - lib/goodcheck/rules.yml

Value of import can be an array of:

  • A string which represents an absolute file path,
  • A string which represents an relative file path from config file, or
  • A http/https URL which represents the location of rules

The rules file is a YAML file with array of rules.

Excluding files

goodcheck.yml can have optional exclude attribute.

rules: []
  - node_modules
  - vendor

Value of exclude can be a string or an array of strings representing the glob pattern for excluded files.


goodcheck init [options]

The init command generates an example of configuration file.

Available options are:

  • -c=[CONFIG], --config=[CONFIG] to specify the configuration file name to generate.
  • --force to allow overwriting existing config file.

goodcheck check [options] targets...

The check command checks your programs under targets.... You can pass:

  • Directory paths, or
  • Paths to files.

When you omit targets, it checks all files in ..

Available options are:

  • -c [CONFIG], --config=[CONFIG] to specify the configuration file.
  • -R [rule], --rule=[rule] to specify the rules you want to check.
  • --format=[text|json] to specify output format.
  • -v, --verbose to be verbose.
  • --debug to print all debug messages.
  • --force to ignore downloaded caches

goodcheck check exits with:

  • 0 when it does not find any matching text fragment
  • 2 when it finds some matching text
  • 1 when it finds some error

You can check its exit status to identify if the tool find some pattern or not.

goodcheck test [options]

The test command tests rules. The test contains:

  • Validation of rule id uniqueness.
  • If pass examples does not match with any of patterns.
  • If fail examples matches with some of patterns.

Use test command when you add new rule to be sure you are writing rules correctly.

Available options is:

  • -c [CONFIG], --config=[CONFIG] to specify the configuration file.
  • -v, --verbose to be verbose.
  • --debug to print all debug messages.
  • --force to ignore downloaded caches

Downloaded rules

Downloaded rules are cached in cache directory in goodcheck home directory. The goodcheck home directory is ~/.goodcheck, but you can customize the location with GOODCHECK_HOME environment variable.

The cache expires in 3 minutes.

Docker Images

You can use Docker images to use Goodcheck. For example:

$ docker pull sider/goodcheck

$ cd /path/to/your/project
$ docker run -it --rm -v "$(pwd):/work" sider/goodcheck goodcheck check


After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to


Bug reports and pull requests are welcome on GitHub.

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