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Log viewer UI and framework for rack

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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

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

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


Logster can be configured using

  • 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
     tag for logster error page.
  • Logster.config.enable_custom_patterns_via_ui
    : enable the settings page (
    ) where you can add suppression and grouping patterns.
  • Logster.config.allow_grouping
    : Enable grouping of similar messages into one messages with an array of
    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
    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
    (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
    . Default value is 1000. In case
    is an array of hashes, this limit applies to the individual hashes in the array rather than the whole array. If an
    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
    , 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
    hashes. This config specifies the maximum number of
    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
    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: "" }]
    . The GitHub links that are constructed will use the
    branch. If you want Logster to use the
    attribute from the
    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.

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

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


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

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

on the message env and the method will fail with

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


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" end

Mount using devise (method 2)

Change :adminuser 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 :adminuser, ->(u) { u.admin? } do mount Logster::Web, at: "/logs" end ```

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

gem in a production deployment on Heroku, the standard
will not cooperate properly with Logster. Extend Rails.logger in your
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
    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.
  5. Once you're done making changes, run
    to make and copy a production build to the assets folder.
  6. Commit your changes (
    git commit -am 'Add some feature'
  7. Push to the branch (
    git push origin my-new-feature
  8. Create a new Pull Request

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