Outputs a source level execution trace of a Ruby program.

It does this by registering an event handler with Kernel#set_trace_func for processing incoming events. It also provides methods for filtering unwanted trace output (see Tracer.add_filter, Tracer.on, and


Add this line to your application's Gemfile:

gem 'tracer'

And then execute:

$ bundle

Or install it yourself as:

$ gem install tracer


Consider the following Ruby script

  class A
    def square(a)
      return a*a

  a =

Running the above script using ruby -r tracer example.rb will output the following trace to STDOUT (Note you can also explicitly require 'tracer')

  #0:<internal:lib/rubygems/custom_require>:38:Kernel:<: -
  #0:example.rb:3::-: class A
  #0:example.rb:3::C: class A
  #0:example.rb:4::-:   def square(a)
  #0:example.rb:7::E: end
  #0:example.rb:9::-: a =
  #0:example.rb:10::-: a.square(5)
  #0:example.rb:4:A:>:   def square(a)
  #0:example.rb:5:A:-:     return a*a
  #0:example.rb:6:A:<:   end
   |  |         | |  |
   |  |         | |   ---------------------+ event
   |  |         |  ------------------------+ class
   |  |          --------------------------+ line
   |   ------------------------------------+ filename
    ---------------------------------------+ thread

Symbol table used for displaying incoming events:

+}+:: call a C-language routine
+{+:: return from a C-language routine
+>+:: call a Ruby method
+C+:: start a class or module definition
+E+:: finish a class or module definition
+-+:: execute code on a new line
+^+:: raise an exception
+<+:: return from a Ruby method


After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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


The gem is available as open source under the terms of the 2-Clause BSD License.