Mathcha is a horribly-named, arithmetic-based, text-driven captcha. Why you ask? For very few good reasons:

  • I had never written a plugin.
  • I wanted to play with a few bits of technology I hadn't touched:
    • git
    • github
    • gemcutter, gem packaging, jeweler
  • I really like Recaptcha it's just that I've seen a few folk using simple math problems; I prefer it.
  • I need this functionality across a few applications I've been working on.


This thing is nascent, fledgling, and was produced in a matter of hours. I haven't thoroughly tested it yet so don't put too much faith in it. Please feel free to fork and dress up. I plan on staying on top of this over the next few weeks and getting something put together that I'm happy to push on my peers.


First, install the gem:

sudo gem install mathcha

Next, modify your config/environment.rb to reference the mathcha gem:

config.gem "mathcha", :source => ""


In your view (this will dump the proper input and a hidden key field)

<%= mathcha_tag %>

In your controller

if (verify_mathcha(params))

Copyright (c) 2009 Cory Wilkerson, released under the MIT license