Switching to a new debugger and potentially changing your debugging process could be scary. So I hope this post can help you get familiar with ruby/debug and determine whether to switch to it.

(In the rest of the article, I'll use debug to refer to ruby/debug)

Disclaimers:

• I'm not as experienced with byebug as with debug. So please let me know if I listed incorrect/outdated information.
• Its purpose is to give a higher-level comparison. To learn more about debug's specific usages, please check its official documentation.
• It doesn't contain all the features but should already cover most of them.

Advantages of debug

Before we get into individual features, I want to quickly mention some advantages of debug:

• Colorized output

  

• Backtrace with method/block arguments

  

• Immune from the compatibility issue with Zeitwerk

• Powerful breakpoints and tracers

• Convenient remote debugging and VSCode integration

  • Setting it up with VSCode

Disadvantages of debug

• Less flexible on thread control
• Doesn't work well with Fiber yet
• Doesn't have pry integration like pry-byebug
• No per-project configuration

byebug vs debug

Installation

(Although Ruby 3.1 comes with debug v1.4, I recommend always using its latest release)

Start Debugging

User Experience Features

Evaluation

Code evaluation in REPL is more or less the same between byebug and debug, that is:

• If the expression doesn't match a console command, like my_method(arg), it'll be evaluated as Ruby code
• If the expression matches a console command, like n, you can use console commands to evaluate it

Flow Control & Frame Navigation

debug provides the same stepping commands as byebug does. So byebug users can switch to debug without learning new behaviors.

Thread Control

As previously mentioned, debug stops all threads when suspended and doesn't allow per-thread management at the moment. So it has simpler thread-related commands.

Breakpoint

Although byebug already has decent breakpoints support, debug takes it to another level by:

• Allowing breakpoints to execute commands with pre: and do: options
• Supporting call-location-based triggering condition with the path: option
• Supporting specialized catch and watch breakpoints

Setting Breakpoints

Managing Breakpoints

Information

Backtrace

Backtrace in debug contains values of method call or block arguments. This small improvement can save you from inspecting them manually between frames.

The filtering support can help you focus on relevant frames and ignore the ones from frameworks or libraries.

Varibles/Constants

Methods

While debug doesn't have a dedicated command to list an object's methods, it has a ls command that's similar to
irb or pry's.

Tracing

I will write another dedicated article to introduce debug's tracing functionalities, but I encourage you to already give them a try from time to time, especially:

• trace exception - to monitor exceptions raised in your code. You may be surprised by the exceptions raised and rescued in your application under the surface.

• trace object <expr> - to observe an object's activities: receiving a method call or being passed to a method call.

  

Configuration

debug supports a wide range of configurations to make it fit your needs. But it doesn't support per-project RC files due to security concerns.

Remote Debugging

Remote debugging functionality is becoming crucial as we start containerizing our development environment and don't always have direct standard IO access.
It's also crucial for connecting to different debugger clients like VSCode or Chrome.

So if you have needs in this area, migrating to debug is your best option.

Wrapping Up

To most users, switching from byebug to debug should take little effort. But the potential productivity gain from debug's features could be significant.

byebug is a great debugger and has served the community well for many years.
But as its development slows down (last release was 2 years ago) and debug receives constant updates from the Ruby core, the gap between them will only widen.

So adding debug to your toolbelt and exploring its powerful features will be a great productivity investment for the long term.

References

• Debugger commands comparison sheet by @ko1
• Byebug's official guide
• ruby/debug's official documentation