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Regexp based customizable linter
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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 for use 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! πŸŽ‰

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 the code reviewing process can be automated. With Goodcheck the only thing you have to do is define the rules, pairing patterns with messages, and then those same patterns won’t bother you anymore. πŸ˜†

Table of contents

  • Installation
  • Quickstart
  • Defining rules
    • Pattern
    • Glob
    • A rule with negated pattern
    • A rule without pattern
    • Triggers
  • Importing rules
  • Excluding files
  • Commands
  • Downloaded rules
  • Disabling rules with inline comments
  • Docker images
  • Development
  • Contributing


$ 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.


$ goodcheck init
$ vim goodcheck.yml
$ goodcheck check

The init command generates a 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.


You can download a printable cheatsheet from this repository.

Defining rules

A goodcheck.yml example of the configuration is like the following:

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

      You may be 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>

A rule hash under a rules list contains the following keys:

  • id - a string to identify rules (required)
  • pattern - a pattern or a sequence of patterns (optional)
  • message - a string to tell writers why the code piece should be revised (required)
  • justification - a sequence of strings to tell writers when an 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 the given pattern (optional)
  • fail - a string or a sequence of strings, which does match the given pattern (optional)


A pattern can be a literal pattern, regexp pattern, token pattern, or a string.

String literal

A string literal represents a literal pattern or regexp pattern.

  - This is a literal pattern
  - /This is a regexp pattern/
  - /This is a regexp pattern with the casefold option/i
  - /This is a regexp pattern with the multiline option/m

If a string value begins with / and ends with /, it is a regexp pattern. You can optionally specify regexp options like /casefold/i or /multiline/m.

Literal pattern

A 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

A 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 expressions can be found in the documentation for Ruby.

Token pattern

A 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 a 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.

Token patterns can have an optional where attribute and variable bindings.

  - token: bgcolor=${color:string}
      color: true

The variable binding consists of a name and type (${name:type}), where color and string in the example above respectively. You have to add a key of the variable name in where attribute.

We have 8 built-in types:

  • string
  • int
  • float
  • number
  • url
  • email
  • word
  • identifier

You can find the exact definitions of the types in the definition of Goodcheck::Pattern::Token (@@TYPES).

You can omit the type of variable binding.

  - token: margin-left: ${size}px;
      size: true
  - token: backgroundColor={${color}}
      color: true

In this case, the following character will be used to detect the range of binding. In the first example above, the px will be used as the marker for the end of size binding.

If parens or brackets are surrounding the variable, Goodcheck tries to match with nested ones in the variable. It expands five levels of nesting. See the example of matches with the second backgroundColor pattern:

  • backgroundColor={color} Matches (color=="color")
  • backgroundColor={{ red: red(), green: green(), blue: green()-1 }} Matches (color=="{ red: red(), green: green(), blue: green()-1 }")
  • backgroundColor={ {{{{{{}}}}}} } Matches (color==" {{{{{{}}}}}")


A glob can be a string or a hash.

glob: "**/test/**/*.rb"
# or
  pattern: "legacy/**/*.rb"
  encoding: EUC-JP
# or
  - "**/test/**/*.rb"
  - pattern: "legacy/**/*.rb"
    encoding: EUC-JP

The hash can have an optional encoding attribute. You can specify the 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 the glob attribute in a rule, the rule will be applied to all files given to goodcheck.

If both your rule and its pattern has glob, Goodcheck will scan the pattern with files matching the glob condition in the pattern.

  - id: glob_test
      - literal: 123      # This pattern applies to .css files
        glob: "*.css"
      - literal: abc      # This pattern applies to .txt files
    glob: "*.txt"

A rule with negated pattern

Goodcheck rules are usually to detect something is included in a file. You can define the negated rules for the opposite, something is missing in a file.

  - id: negated
      pattern: <!DOCTYPE html>
    message: Write a doctype on HTML files.
    glob: "**/*.html"

A rule without pattern

You can define a rule without pattern. The rule emits an issue on each file specified with glob. You cannot omit glob from a rule definition without pattern.

  - id: without_pattern
    message: |
      Read the operation manual for DB migration:
    glob: db/schema.rb

The output will be something like:

$ goodcheck check
db/schema.rb:-:# This file is auto-generated from the current state of the database. Instead: Read the operation manual for DB migration:


Version 2.0.0 introduces a new abstraction to define patterns, called trigger. You can continue using patterns in rule, but using trigger allows more flexible pattern definition and more precise testing.

  - id: trigger
    message: Using trigger
      - pattern: <blink
        glob: "**/*.html"
          - <blink></blink>
      - not:
            token: <meta charset="UTF-8">
            case_sensitive: false
        glob: "**/*.html"
        pass: |
            <meta charset="utf-8"></meta>

You can continue existing pattern definitions, but using goodcheck test against patterns with glob does not work. If your pattern definition includes glob, switching to trigger would make sense.

Importing rules

goodcheck.yml can have an optional import attribute.

  - /usr/share/goodcheck/rules.yml
  - lib/goodcheck/rules.yml

The value of import can be a sequence of:

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

The rules file is a YAML file with an sequence of rules:

- id: rule1
  pattern: Some pattern 1
  message: Some message 1

- id: rule2
  pattern: Some pattern 2
  message: Some message 2

# ...

Excluding files

goodcheck.yml can have an optional exclude attribute.

  - node_modules
  - vendor
  - **/test/**/*.txt

The value of exclude can be a string or a sequence of strings representing the glob pattern for excluded files.


goodcheck init [options]

The init command generates an example of a configuration file.

Available options are:

  • -c=[CONFIG], --config=[CONFIG] to specify the configuration file name to generate.
  • --force to allow overwriting of an 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 . (the current directory).

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 finds 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 a new rule to be sure you are writing rules correctly.

Available options are:

  • -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.

goodcheck pattern [options] ids...

The pattern command prints the regular expressions generated from the patterns. The command is for debugging patterns, especially token patterns.

The available option is:

  • -c [CONFIG], --config=[CONFIG] to specify the configuration file.

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.

Disabling rules with inline comments

You can disable rule warnings on a specific line using line comments supported by common languages.

For example, for Ruby:

# goodcheck-disable-next-line
puts "Github"
puts "Github" # goodcheck-disable-line

For JavaScript:

// goodcheck-disable-next-line
console.log("Github") // goodcheck-disable-line

Docker images

We provide Docker images of Goodcheck on Docker Hub so that you can try Goodcheck without installing them.

$ docker pull sider/goodcheck
$ docker run -t --rm -v "$(pwd):/work" sider/goodcheck check

The default latest tag points to the latest release of Goodcheck. You can pick a version of Goodcheck from the Docker Hub tags page.


After checking out the repository, 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, follows the steps below:

  1. Update the version number in version.rb.
  2. Add the new version's entry to the changelog.
  3. Update the documentation via bundle exec rake docs:update_version.
  4. Commit the above changes like git commit -m 'Version 1.2.3'.
  5. 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
  6. Publish the updated documentation like GIT_USER=some_user USE_SSH=true bundle exec rake docs:publish.


Bug reports and pull requests are welcome on GitHub.