🍯 Unobtrusive and flexible spam protection for Rails apps
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Invisible Captcha

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Simple and flexible spam protection solution for Rails applications.

Invisible Captcha provides different techniques to protect your application against spambots.

The main protection is a solution based on the honeypot principle, which provides a better user experience, since there is no extra steps for real users, but for the bots.

Essentially, the strategy consists on adding an input field 🍯 into the form that:

  • shouldn't be visible by the real users
  • should be left empty by the real users
  • will most be filled by spam bots

It also comes with a time-sensitive ⌛️ form submission.


Invisible Captcha is tested against Rails >= 3.2 and Ruby >= 2.2.

Add this line to you Gemfile:

gem 'invisible_captcha'

Or install the gem manually:

$ gem install invisible_captcha


View code:

<%= form_for(@topic) do |f| %>
  <%= f.invisible_captcha :subtitle %>
  <!-- or -->
  <%= invisible_captcha :subtitle, :topic %>
<% end %>

Controller code:

class TopicsController < ApplicationController
  invisible_captcha only: [:create, :update], honeypot: :subtitle

This method will act as a before_action that triggers when spam is detected (honeypot field has some value). By default it responds with no content (only headers: head(200)). This is a good default, since the bot will surely read the response code and will think that it has achieved to submit the form properly. But, anyway, you are able to define your own callback by passing a method to the on_spam option:

class TopicsController < ApplicationController
  invisible_captcha only: [:create, :update], on_spam: :your_spam_callback_method


  def your_spam_callback_method
    redirect_to root_path

Note that is not mandatory to specify a honeypot attribute (nor in the view, nor in the controller). In this case, the engine will take a random field from InvisibleCaptcha.honeypots. So, if you're integrating it following this path, in your form:

<%= form_tag(new_contact_path) do |f| %>
  <%= invisible_captcha %>
<% end %>

In you controller:

invisible_captcha only: [:new_contact]

Options and customization

This section contains a description of all plugin options and customizations.

Plugin options:

You can customize:

  • sentence_for_humans: text for real users if input field was visible. By default, it uses I18n (see below).
  • honeypots: collection of default honeypots. Used by the view helper, called with no args, to generate a random honeypot field name. By default, a random collection is already generated.
  • visual_honeypots: make honeypots visible, also useful to test/debug your implementation.
  • timestamp_threshold: fastest time (in seconds) to expect a human to submit the form (see original article by Yoav Aner outlining the idea). By default, 4 seconds. NOTE: It's recommended to deactivate the autocomplete feature to avoid false positives (autocomplete="off").
  • timestamp_enabled: option to disable the time threshold check at application level. Could be useful, for example, on some testing scenarios. By default, true.
  • timestamp_error_message: flash error message thrown when form submitted quicker than the timestamp_threshold value. It uses I18n by default.
  • injectable_styles: if enabled, you should call anywhere in your layout the following helper <%= invisible_captcha_styles %>. This allows you to inject styles, for example, in <head>. False by default, styles are injected inline with the honeypot.

To change these defaults, add the following to an initializer (recommended config/initializers/invisible_captcha.rb):

InvisibleCaptcha.setup do |config|
  # config.honeypots           << ['more', 'fake', 'attribute', 'names']
  # config.visual_honeypots    = false
  # config.timestamp_threshold = 4
  # config.timestamp_enabled   = true
  # config.injectable_styles   = false

  # Leave these unset if you want to use I18n (see below)
  # config.sentence_for_humans     = 'If you are a human, ignore this field'
  # config.timestamp_error_message = 'Sorry, that was too quick! Please resubmit.'

Controller method options:

The invisible_captcha method accepts some options:

  • only: apply to given controller actions.
  • except: exclude to given controller actions.
  • honeypot: name of custom honeypot.
  • scope: name of scope, ie: 'topic[subtitle]' -> 'topic' is the scope.
  • on_spam: custom callback to be called on spam detection.
  • timestamp_enabled: enable/disable this technique at action level.
  • on_timestamp_spam: custom callback to be called when form submitted too quickly. The default action redirects to :back printing a warning in flash[:error].
  • timestamp_threshold: custom threshold per controller/action. Overrides the global value for InvisibleCaptcha.timestamp_threshold.

View helpers options:

Using the view/form helper you can override some defaults for the given instance. Actually, it allows to change: sentence_for_humans and visual_honeypots.

<%= form_for(@topic) do |f| %>
  <%= f.invisible_captcha :subtitle, visual_honeypots: true, sentence_for_humans: "hey! leave this input empty!" %>
  <!-- or -->
  <%= invisible_captcha visual_honeypots: true, sentence_for_humans: "hey! leave this input empty!" %>
<% end %>

You can also pass html options to the input:

<%= invisible_captcha :subtitle, :topic, id: "your_id", class: "your_class" %>


invisible_captcha tries to use I18n when it's available by default. The keys it looks for are the following:

    sentence_for_humans: "If you are human, ignore this field"
    timestamp_error_message: "Sorry, that was too quick! Please resubmit."

You can override the english ones in your own i18n config files as well as add new ones for other locales.

If you intend to use I18n with invisible_captcha, you must not set sentence_for_humans or timestamp_error_message to strings in the setup phase.


Any kind of idea, feedback or bug report are welcome! Open an issue or send a pull request.


Clone/fork this repository, start to hack on it and send a pull request.

Run the test suite:

$ bundle exec rspec

Run the test suite against all supported versions:

$ bundle exec appraisal install
$ bundle exec appraisal rspec

Run specs against specific version:

$ bundle exec appraisal rails-5.2 rspec


Start a sample Rails app (source code) with InvisibleCaptcha integrated:

$ bundle exec rake web # PORT=4000 (default: 3000)


Copyright (c) Marc Anguera. Invisible Captcha is released under the MIT License.