Setup ruby/debug with VSCode


2 min read

Do you know Ruby's official debugger ruby/debug provides out-of-box integration with VSCode? If you haven't tried it yet or having difficulty making it work, I hope this short post will help you set it up.

Basic Setup

  1. Install the VSCode rdbg extension in VSCode
  2. Create the launch.json file
    1. Click Run and Debug button on the left side
    2. Click create a launch.json file - this is quite small and under To customize Run and Debug
    3. Save the created launch.json
  3. Put gem "debug", require: false in your Gemfile and run bundle install

Debug Simple Ruby Script

If you want to debug a simple Ruby script, you can follow these steps.

Debug Rails/Web Applications

If you want to debug a Rails/web application, do these instead:

  1. Open the files in VSCode and add some breakpoints.
  2. Start your program with the rdbg executable - bundle exec rdbg --open -n -c -- bundle exec rails s
    • --open or -O means starting the debugger in server mode
    • -n means don't stop at the beginning of the program, which is usually somewhere at rubygems, not helpful
    • -c means you'll be running a Ruby-based command
  3. Go back to VSCode's Run and Debug panel, you should see a grean play button
  4. Click the dropdown besides the button and select Attach with rdbg
  5. Click the play button
  6. It should now connect the VSCode to the debugger
    • If it stops at somewhere in your web server (like puma), please upgrade to the latest version (v1.6.0+)
  7. Send some requests and it should stop at your breakpoints


Connect the debugger with your Rails server

I also have built this to let you try out ruby/debug's console commands in your browser (it'll only take you 5 minutes).

If you want to see more articles/tips about the powerful features ruby/debug has, you can follow me on Twitter 🙂