There's a lot of open issues
No release in over a year
Querly is a query language and tool to find out method calls from Ruby programs. Define rules to check your program with patterns to find out *bad* pieces. Querly finds out matching pieces from your program.


~> 1.0.13
>= 1.12
~> 5.0.4
~> 5.0
>= 1.4.14
~> 13.0
~> 4.0.1


~> 1.17
>= 2.1
>= 0.19.0
>= 3.0
 Project Readme

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Querly - Pattern Based Checking Tool for Ruby


Querly is a query language and tool to find out method calls from Ruby programs. Define rules to check your program with patterns to find out bad pieces. Querly finds out matching pieces from your program.


Your project may have many local rules:

  • Should not use Customer#update_mail and use 30x faster Customer.update_all_email instead (Slower #update_mail is left just for existing code, but new code should not use it)
  • Should not use root_url without locale: parameter
  • Should not use Net::HTTP for Web API calls, but use HTTPClient

These local rule violations will be found during code review. Reviewers will ask commiter to revise; commiter will fix; fine. Really? It is boring and time-consuming. We need some automation!

However, that rules cannot be the standard. They make sense only in your project. Okay, start writing a plug-in for RuboCop? (or other checking tools)

Instead of writing RuboCop plug-in, just define a Querly rule in a few lines of YAML.

  - id: my_project.use_faster_email_update
    pattern: update_mail
    message: When updating Customer#email, newly written code should use 30x faster Customer.update_all_email
      - When you are editing old code (it should be refactored...)
      - You are sure updating only small number of customers, and performance does not matter

  - id: my_project.root_url_without_locale
    pattern: "root_url(!locale: _)"
    message: Links to top page should be with locale parameter

  - id: my_project.net_http
    pattern: Net::HTTP
    message: Use HTTPClient to make HTTP request

Write down your local rules, and let Querly check conformance with them. Focus on spec, design, UX, and other important things during code review!


Install via RubyGems.

$ gem install querly

Or you can put it in your Gemfile.

gem 'querly'

Quick Start

Copy the following YAML and paste as querly.yml in your project's repo.

  - id: sample.debug_print
      - self.p
      - self.pp
    message: Delete debug print

Run querly in the repo.

$ querly check .

If your code contains p or pp calls, querly will print warning messages.

./app/models/account.rb:44:10                  p(      Delete debug print
./app/controllers/accounts_controller.rb:17:2  pp params: params  Delete debug print


See the following manual for configuration and query language reference.

Use querly console command to test patterns interactively.

Requiring Rules

import section in config file now allows accepts require command.

  - require: querly/rules/sample
  - require: your_library/querly/rules

Querly ships with querly/rules/sample rule set. Check lib/querly/rules/sample.rb and rules/sample.yml for detail.

Publishing Gems with Querly Rules

Querly provides Querly.load_rule API to allow publishing your rules as part of Ruby library. Put rules YAML file in your gem, and add Ruby script in some directory like lib/your_library/querly/rules.rb.

Querly.load_rules File.join(__dir__, relative_path_to_yaml_file)


Querly's analysis is syntactic

The analysis is currently purely syntactic: false)


x = false x)

will yield different results. This can be improved by doing very primitive data flow analysis, and I'm planning to do that.

Too many false positives!

The analysis itself does not have very good precision. There will be many false positives, and querly warning free code does not make much sense.

  • TODO: support to ignore warnings through magic comments in code

Querly is not to ensure there is nothing wrong in the code, but just tells you code fragments you should review with special care. I believe it still improves your software development productivity.

Incoming updates?

The following is the list of updates which would make sense.

  • Support for importing rule sets, and provide some good default rules
  • Support for ignoring warnings
  • Improve analysis precision by intra procedural data flow analysis


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 at