A long-lived project that still receives updates
UI for viewing logs in Rack


 Project Readme

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Logster is an embedded Ruby "exception reporting service" admins can view on live websites, at



Play with a live demo at


Add these lines to your application's Gemfile:

gem 'redis'
gem 'logster'

And then execute:

$ bundle

To make logster web available add the following to your routes.rb:

constraints lambda { |req| req.session["admin"] } do
  mount Logster::Web => "/logs"

By default, logster will only run in development and production environments.

To run logster in other environments, in config/application.rb

Logster.set_environments([:development, :staging, :production])


Logster can be configured using Logster.config:

  • Logster.config.application_version: set to a unique identifier denoting version of your app. The "solve" function takes this version into account when suppressing errors.

  • Logster.config.enable_js_error_reporting : enable js error reporting from clients

  • Logster.config.rate_limit_error_reporting : controls automatic 1 minute rate limiting for JS error reporting.

  • Logster.config.web_title : <title> tag for logster error page.

  • Logster.config.enable_custom_patterns_via_ui : enable the settings page (/settings) where you can add suppression and grouping patterns.

  • Logster.config.allow_grouping : Enable grouping of similar messages into one messages with an array of env of the grouped messages. Similar messages are messages that have identical backtraces, severity and log message.

  • Logster.config.maximum_message_length : set a maximum length for log messages that are shown inside the info tab and in the message rows in the UI. Messages that exceed the specified length will be truncated and an ellipsis will be appended to indicate that the message has been truncated. Default value is 2000.

  • Logster.config.maximum_message_size_bytes : set a maximum size for message objects. Default value is 10,000. If a message size exceeds this limit, Logster will first remove all occurrences of gems_dir (more on this config below) from the backtrace and computes the size again; if the message is still above the limit, Logster will remove as many as character as needed from the backtrace to bring the size below the limit. It's discouraged to set this config to a really low value (e.g. less than 2000) because a message needs a minimum amount of data in order to make sense (the minimum amount varies per message), so the closer the limit is to the minimum amount of space needed, the more of the backtrace will be removed. Keep this in mind when tweaking this config.

  • Logster.config.max_env_bytes : set a maximum size for env. Default value is 1000. In case env is an array of hashes, this limit applies to the individual hashes in the array rather than the whole array. If an env hash exceeds this limit, Logster will take the biggest subset of key-value pairs whose size is below the limit. If the hash has a key with the name time, it will always be included.

  • Logster.config.max_env_count_per_message : default value is 50. Logster can merge messages that have the same backtrace, severity and log message into one grouping message that have many env hashes. This config specifies the maximum number of env hashes a grouping message is allowed to keep. If this limit is reached and a new similar message is created and it needs to be merged, Logster will remove the oldest env hash from the grouping message and adds the new one.

  • Logster.config.project_directories : This should be an array of hashes that map paths on the local filesystem to GitHub repository URLs. If this feature is enabled, Logster will parse backtraces and try to construct a GitHub URL to the exact file and line number for each line in the backtrace. For a Rails app, the config may look like this: Logster.config.project_directories = [{ path: Rails.root.to_s, url: "<your_org>/<your_repo>" }]. The GitHub links that are constructed will use the master branch. If you want Logster to use the application_version attribute from the env tab so that the GitHub links point to the exact version of the app when the log message is created, add main_app: true key to the hash.

  • Logster.config.enable_backtrace_links : Enable/disable the backtrace links feature.

  • Logster.config.gems_dir : The value of this config is Gem.dir + "/gems/" by default. You probably don't need to change this config, but it's available in case your app gems are installed in a different directory. An example where this config is needed is Logster demo site:

Tracking Error Rate

Logster allows you to register a callback when the rate of errors has exceeded a given limit.

Tracking buckets available are one minute and an hour.


Logster.register_rate_limit_per_minute(Logger::WARN, 60) do |rate|
  puts "O no! The error rate is now #{rate} errors/min"

Logster.register_rate_limit_per_hour([Logger::WARN, Logger::ERROR, Logger::FATAL], 60) do |rate|
  puts "O no! The error rate is now #{rate} errors/hour"


If you are seeing the error No such middleware to insert before: ActionDispatch::DebugExceptions after installing logster, then you are using a conflicting gem like better_errors or web-console.

To avoid this error, make sure logster is added behind those conflicting gems in your Gemfile.

If you're using Logster with a non-rails app, you'll need to be careful that the env hashes of messages that Logster receives don't contain strings with invalid encoding because at some point Logster calls #to_json on the message env and the method will fail with JSON::GeneratorError.

The reason this doesn't happen in rails apps is because ActiveSupport has a monkey patch for #to_json.

Mount using warden (devise)

  admin_constraint = lambda do |request|
    request.env['warden'].authenticate? and request.env['warden'].user.admin?

  constraints admin_constraint do
    mount Logster::Web, at: "/logs"

Mount using devise (method 2)

Change :admin_user symbol with your devise user, example :user. In -> lambda block change admin? method with your authorization method Or simply define a admin? method in you user model.

  authenticate :admin_user, ->(u) { u.admin? } do
    mount Logster::Web, at: "/logs"

Out of the box, logster will use the default redis connection, to customise, in config/application.rb =

Heroku Deployment

In case you may be using the rails_12factor gem in a production deployment on Heroku, the standard Rails.logger will not cooperate properly with Logster. Extend Rails.logger in your config/application.rb or config/initializers/logster.rb with:

if Rails.env.production?


Logster UI is built using Ember.js


  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Run cd client-app && npm install
  4. Run cd website && bundle install
  5. Run bundle exec rake client_dev to start Sinatra server (port 9292) and Ember server (port 4200). Use Ember server for hot reload for client code.
  6. Once you're done making changes, run ./ to make and copy a production build to the assets folder.
  7. Commit your changes (git commit -am 'Add some feature')
  8. Push to the branch (git push origin my-new-feature)
  9. Create a new Pull Request