rubocop-kata

A RuboCop plugin that replaces a pile of linter gems and config with one dependency. Install it and your .rubocop.yml shrinks to project-specific overrides. Everything else comes from the gem: a curated stack of RuboCop extensions, opinionated style defaults, and fifteen house cops.

Kata/GoodMethodName asks for one word per method name. A second word is allowed only when it is not hiding a missing object: a role prefix (after_fork), a role suffix (file_of), or a compound noun you have added to Terms on purpose. The wrong way to satisfy the cop is matching_ids → matchingids: if you need two words, that is a modelling smell — the concept is missing, or the method belongs on a different object. Kata/RealWords catches that dodge with a shipped dictionary instead of a word list you maintain: matchingids is not a word, so it fails with zero configuration — and so does cfg.

  • One dependency. Bundles rubocop-rspec, rubocop-performance, rubocop-elegant, rubocop-packaging, and rubocop-thread_safety behind a single gem.
  • Opinionated defaults. Methods under 5 lines, classes under 100, 4 parameters max, 120-column lines, double quotes, NewCops: enable. See config/default.yml.
  • Fifteen house cops. Naming, dependency discipline, and data honesty in the Elegant Objects spirit — from Kata/AgentNoun to Kata/ClockDiscipline.
class PaymentProcessor  # Kata/AgentNoun: `PaymentProcessor` names a doer;
end                     #   name the class for the thing it is, not the work it does.

class Payment           # OK
end

Getting started

Add the gem to your Gemfile:

gem "rubocop-kata", group: :development, require: false

Install it and point .rubocop.yml at the plugin:

plugins:
  - rubocop-kata

AllCops:
  TargetRubyVersion: 3.4

bundle install
bundle exec rubocop

That's it. The plugin loads the bundled extensions and the shared defaults, so your .rubocop.yml keeps only what's specific to your project. Requires Ruby >= 3.4 and RuboCop ~> 1.75.

The cops

Cop Default What it enforces
Kata/AgentNoun on Classes named for what they are, not -er/-or doers. Allow exceptions via AllowedNames.
Kata/NoComments on No prose comments; say it in the code. Magic comments, linter directives, and licence headers survive. Autocorrects.
Kata/IoDiscipline on No bare puts/warn/pp/p outside specs/scripts; write through an injected @io or an explicit receiver.
Kata/ProsePlacement off Sentence-length strings belong in the presentation layer. Enable with an Include/Exclude matching your layering.
Kata/NoUtilName on No junk-drawer names (Util, Helper, Manager, Service, …). Tune via BannedNames.
Kata/RealWords on Every name segment is a word the shipped dictionary knows — errorcount (smash) and cfg (abbreviation) both fail, with no word list to maintain. Tune via Terms/BannedWords/AllowedNames.
Kata/GoodMethodName on One word per method name; a second word needs a role prefix (after_fork), a role suffix (file_of), or a reviewed Terms entry. Tune via MaxWords/Prefixes/Suffixes/Terms/AllowedNames.
Kata/GoodVariableName on The same rule for locals, parameters, ivars, class variables, and globals; _name and @_name stay exempt.
Kata/BuilderNoun on Builders named for what they return: total, not calculate_total. Tune via BannedPrefixes.
Kata/NoBooleanFlag on No positional boolean arguments; split the method or use a keyword.
Kata/ConstructorDiscipline on initialize assigns, raises, or freezes — never computes.
Kata/NoClassMethodLogic on Class methods construct (build, parse, of, from_*); instances do the work.
Kata/NoHashAsObject on A hash with MaxKeys+ keys (default 4) wants to be an object. Keyword-argument call sites exempt.
Kata/ClockDiscipline on No bare Time.now/Date.today/.current; inject a clock.
Kata/EnvDiscipline on ENV reads only in the boot layer (config/, bin/, exe/).

The defaults

Double-quoted strings, Metrics/MethodLength: 5, Metrics/ClassLength: 100, Metrics/ParameterLists: 4, 120-column lines, endless methods on one line, rescue => error, NewCops: enable, and heredocs counted as one line in spec examples. See config/default.yml.

License

The code is MIT — see LICENSE.txt. The shipped dictionaries are third-party data under their own terms:

  • data/words.txt.gz — a modified subset of SCOWL en-US size 60: filtered, deduplicated, and gzipped. SCOWL is the collective work of Kevin Atkinson and the contributors named in data/SCOWL-COPYRIGHT, which is distributed with this gem and reproduced verbatim. It includes, among others, Copyright 2000–2018 Kevin Atkinson; WordNet 1.6 Copyright 1997 by Princeton University, all rights reserved; and Copyright 1993 Geoff Kuenning, Granada Hills, CA, all rights reserved. Princeton University makes no representations or warranties, express or implied, as to this database, and its name may not be used in advertising or publicity pertaining to this distribution.
  • data/software.txt.gz — built from the software-terms, ruby, and shell dictionaries of cspell-dicts, each MIT-licensed. Copyright (c) 2017–2025 Street Side Software; the notice and permission text are reproduced in data/CSPELL-LICENSE.
  • data/supplement.txt — this project's own additions, MIT.