Renders KaTeX from Ruby.
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KaTeX for Ruby Build Status Test Coverage Code Climate

This rubygem enables you to render TeX math to HTML using KaTeX. It uses ExecJS under the hood.


Add this line to your application's Gemfile:

gem 'katex', '~> 0.5.0'

And then execute:

$ bundle

Or install it yourself as:

$ gem install katex


Render some math:

Katex.render 'c = \\pm\\sqrt{a^2 + b^2}'
#=> "<span class=\"katex\">..."

If you're on Rails, the result is marked as html_safe.

Any error in the markup is raised by default. To avoid this and render error text instead, pass throw_on_error: false:

Katex.render '\\', throw_on_error: false

Note that this will catch even ParseErrors (unlike native KaTeX).

Learn more about all the available options in the documentation.


For this rendered math to look nice, you will also need to include KaTeX CSS into the webpage.

I recommend you use the CSS bundled with this gem, to ensure version compatibility.

Automatic registrations

If you use Rails, Sprockets without Rails, or Hanami, the assets are registered automatically.

Simply //= require katex if you use CSS or @import "_katex" if you use Sass.

You can also //= require katex in your JS to access the KaTeX renderer in the browser.

Manual registration

The assets are located in the vendor/assets directory of the gem. The root path to the root directory of the gem is available via Katex.gem_path, e.g.:

File.join(Katex.gem_path, 'vendor', 'assets')

KaTeX version

The version of KaTeX bundled with this gem is available via:



If you cache the output of Katex.render, make sure to use the KaTeX version in the cache key, as the output may change between versions.


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


Bug reports and pull requests are welcome on GitHub at

This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


The gem is available as open source under the terms of the MIT License.