ruby-debug is a fast implementation of the standard debugger debug.rb. The faster execution speed is achieved by utilizing a new hook in the Ruby C API.


ruby-debug requires Ruby 1.8.4 or higher.

Unless you get the packages as a binary (Microsoft Windows binaries are sometimes available), you'll need a C compiler and Ruby development headers, and a Make program so the extension in ruby-debug-base can be compiled when it is installed.

To install on Microsoft Windows, unless you run under cygwin or mingw you'll need Microsoft Visual C++ 6.0 also known as VC6. suggests why.


ruby-debug is provided as a RubyGem. To install:

gem install ruby-debug

This should also pull in ruby-debug-base as a dependency.

(If you install ruby-debug-base explicitly, you can add in the --test option after “install” to have the regression test run before installing.)

For Emacs support and the Reference Manual, get ruby-debug-extra. This is not a RubyGem, you'll need a Make program and a POSIX shell. With this installed, run:

sh ./configure
make test # optional, but a good idea
sudo make install

Install on MS Windows

Compiling under cygwin or mingw works like it does on Unix.

  • Have Microsoft Visual C++ 6.0 (VC6) installed - exactly that version.

  • Set the appropriate environment variables.

  • run `nmake'.

  • Copy to `win32'.

  • Go to the ruby_debug root.

  • rake win32_gem

  • The file is in named `rdebug-debug-base-0.10.0-mswin32.gem'.


There are two ways of running ruby-debug.

rdebug executable:

$ rdebug <your-script>

When you start your script this way, the debugger will stop at the first line of code in the script file. So you will be able to set up your breakpoints.

ruby-debug API

The second way is to use the ruby-debug API to interrupt your code execution at run time.

require 'ruby-debug' ; Debugger.start
def your_method


require 'ruby-debug' ; 
Debugger.start do 

When Kernel#debugger method is executed, the debugger is activated and you will be able to inspect and step through your code.


The debug.rb script that comes with the standard Ruby library uses Kernel#set_trace_func API. Implementing the debugger in pure Ruby has a negative impact on the speed of your program execution. This is because the Ruby interpreter creates a Binding object each trace call, even though it is not being used most of the time. ruby-debug moves most of the functionality for Binding access and for breakpoint testing to a native extension. Because this code is in C and because and can be selectively enabled or disabled, the overhead in running your program can be minimized.


See LICENSE for license information.

ruby-debug-base for JRuby


(j)ruby-debug-base provides the fast debugger extension for JRuby interpreter. It is the same as ruby-debug-base native C extension from ruby-debug project (, but for JRuby.


(j)ruby-debug-base is available as a RubyGem:

jruby -S gem install ruby-debug-base


The usage is then the same as with native ruby-debugger, but you might need to force JRuby which has to run in interpreted mode. Simplest usage is:

$ jruby --debug -S rdebug <your-script>

Or easier, you might create 'jruby-dm' ('dm' for 'debugger-mode'):

$ cat ~/bin/jruby-dm
jruby --debug "[email protected]"

Then you may run just as you used to:

$ jruby-dm -S rdebug <your-script>

For more information see:

To build run:

$ rake java gem


See MIT-LICENSE for license information.