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Spell check your source code for fun and occasionally finding bugs

This is inspired by https://github.com/myint/scspell, and uses wordlists from SCOWL and MDN.

What makes a spell checker a source code spell checker?

  1. It tokenizes CamelCase and snake_case and kebab-case and checks these as independent words including CAMELCase with acronyms.
  2. It skips urls
  3. It skips things that heuristically look like base64 or hex strings rather than words. This uses a bayesian classifier and is not magic. Find the balance of false-positive to false-negative that works for you with the key_heuristic_weight configuration option.
  4. It comes with some wordlists for built in commands in some common programming languages, and recognizes hashbangs.
  5. Configure whether you want US, AU, CA, or GB english (or all of them).
  6. It checks directories recursively, obeying .gitignore
  7. It's easy to add terms to wordlists
  8. It's easy to integrate with CI pipelines
  9. It's very configurable

A brief aside on "correct" spelling.

There's no correct way to spell anything. You can't trust dictionaries, they only react to the way everyone else uses words. Any agreement about certain spellings is a collective hallucination, and is a terrible proxy for attention or intelligence or education or value. Those who get to declare what "correct" spelling is, or even what counts as a real word, tend to be those groups that have more social power and it's (sometimes unconsciously) used as a way to maintain that power.

However, in a programming context spelling things consistently is useful, where method definitions must match method calls, and comments about these are clearer when also matching. It also makes grepping easier, not that you'd find the word 'grepping' in most dictionaries.


With Bundler

Add this line to your application's Gemfile:

gem 'spellr', require: false

Then execute:

$ bundle install

With Rubygems

$ gem install spellr

With Docker

execute this command instead of spellr. This is otherwise identical to using the gem version

$ docker run -it -v $PWD:/app robotdana/spellr


The main way to interact with spellr is through the executable.

$ spellr # will run the spell checker
$ spellr --interactive # will run the spell checker, interactively
$ spellr --wordlist # will output all words that fail the spell checker in spellr wordlist format
$ spellr --quiet # will suppress all output

To check a single file or subset of files, just add paths or globs:

$ spellr --interactive path/to/my/file.txt and/another/file.sh
$ spellr --wordlist '*.rb' '*_test.js'

There are some support commands available:

$ spellr --dry-run # list files that will be checked
$ spellr --version # for the current version
$ spellr --help # for the list of flags available

First run

Feel free to just spellr --interactive and go, but I prefer this process when first adding spellr to a large project.

$ spellr --dry-run

Look at the list of files, are there some that shouldn't be checked (generated files etc)? .gitignored files and some binary file extensions are already skipped by default.

Add any additional files to ignore to a .spellr.yml file in your project root directory.

  - ignore
  - /generated
  - "!files"
  - in/*
  - .gitignore
  - "*.format"

Then output the existing words that fail the default dictionaries.

$ spellr --wordlist > .spellr-wordlists/english.txt

Open .spellr-wordlists/english.txt and remove those lines that look like typos or mistakes, leaving the file in ascii order.

Now it's time to run the interactive spell checker

$ spellr --interactive

Interactive spell checking

To start an interactive spell checking session:

$ spellr --interactive

You'll be shown each word that's not found in a dictionary, it's location (path:line:column), along with a prompt.

file.rb:1:0 notaword

Type ? for this list of what each letter command does

[r] Replace notaword
[R] Replace all future instances of notaword
[s] Skip notaword
[S] Skip all future instances of notaword
[a] Add notaword to a word list
[e] Edit the whole line
[?] Show this help

If you type r, R or e you'll be shown a prompt with the original word and it prefilled ready for correcting:

file.txt:1:0 notaword
>> notaword
=> not_a_word

To submit your choice and continue with the spell checking click enter. Your replacement word will be immediately spellchecked. To instead go back press Ctrl-C once (pressing it twice will exit the spell checking).

If you instead type s or S it will skip this word and continue with the spell checking.

If you instead type a you'll be shown a list of possible wordlists to add to. This list is based on the file path, and is configurable in .spellr.yml.

Add notaword to wordlist:
[e] english
[r] ruby

Type e to add this word to the english wordlist and continue on through the spell checking. To instead go back to the prompt press Ctrl-C once (pressing it twice will exit the spell checking).

Disabling the tokenizer

If the tokenizer finds a word you don't want to add to the wordlist (perhaps it's an intentional example of a typo, or a non-word string not excluded by the heuristic) then place on the lines before and after

# spellr:disable
"Test typo of the: teh"
# spellr:enable


Spellr's configuration is a .spellr.yml file in your project root. This is combined with the gem defaults defined here. There are top-level keys and per-language keys.

word_minimum_length: 3 # any words shorter than this will be ignored
key_minimum_length: 6 # any strings shorter than this won't be considered non-word strings
key_heuristic_weight: 5 # higher values mean strings are more likely to be considered words or non-words by the classifier.
  - ignore
  - "!files"
  - in/*
  - .gitignore
  - "*.format"
  - limit to
  - "files*"
  - in/*
  - .gitignore-esque
  - "*.format"

The includes format is documented here.

Also within this file are language definitions:

  english: # this must match exactly the name of the file in .spellr-wordlists/
    locale: # US, AU, CA, or GB
      - US
      - AU
      - patterns*
      - "*_here.rb"
      - limit-which-files
      - the/wordlist/**/*
      - /applies_to/
    key: r # this is the letter used to choose this wordlist when using `spellr --interactive`.
      - ruby # if the hashbang contains ruby, this file will match,
             # even if it doesn't otherwise match the includes pattern.


After checking out the repo, run bin/setup to install dependencies. Then, run rake spec 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 rubygems.org.


Bug reports and pull requests are welcome on GitHub at https://github.com/robotdana/spellr.


The gem is available as open source under the terms of the MIT License. Wordlists packaged with this gem have their own licenses, see them in https://github.com/robotdana/spellr/tree/master/wordlists