In Rails 5, byebug is a standard debugger to trace program execution flow and inspect the call stack within an application. From Rails 7, byebug has been replaced with ruby/debug and it comes with colors to highlight syntax. ruby/debug is included in Ruby 3.1 onwards.
<h3 id="heading-hit-and-evaluate">Hit and evaluate</h3>
Let's say someone enters an URL <code>localhost:3000/subjects/1</code> in the browser, it will then call <code>show</code> method in subject controller with parameter id 1. The browser shows non-stop spinning circle and once we open up our terminal, it reaches to a debugger breakpoint
<pre><code class="lang-ruby"> # app/controllers/subject_controller.rb 
 8| def show
 9| @subject = Subject.find(params[:id])
=&gt; 10| binding.break
 11| render json: @subject
 12| end
 13| end
</code></pre>
and if we trace the <code>subject</code> instance variable, it will return us the subject with id 1.
<pre><code class="lang-ruby">(ruby) @subject
#&lt;Subject:0x000000010a852e00
 id: 1,
 name: "Data Structures and Algorithms",
 code: "COMP9xxx",
 created_at: Mon, 05 Dec 2022 08:36:16.828535000 UTC +00:00,
 updated_at: Mon, 05 Dec 2022 08:38:13.160839000 UTC +00:00&gt;
(rdbg) c # continue command
Completed 200 OK in 10259ms (Views: 0.5ms | ActiveRecord: 0.4ms | Allocations: 106092)
</code></pre>
In a high-level overview, both byebug and ruby/debug are working similarly.

In Rails 5, byebug is a standard debugger to trace program execution flow and inspect the call stack within an application. From Rails 7, byebug has been replaced with ruby/debug and it comes with colors to highlight syntax. ruby/debug is included in Ruby 3.1 onwards.

### Hit and evaluate

Let's say someone enters an URL `localhost:3000/subjects/1` in the browser, it will then call `show` method in subject controller with parameter id 1. The browser shows non-stop spinning circle and once we open up our terminal, it reaches to a debugger breakpoint

```ruby
 # app/controllers/subject_controller.rb 
 8| def show
 9| @subject = Subject.find(params[:id])
=> 10| binding.break
 11| render json: @subject
 12| end
 13| end
```

and if we trace the `subject` instance variable, it will return us the subject with id 1.

```ruby
(ruby) @subject
#<Subject:0x000000010a852e00
 id: 1,
 name: "Data Structures and Algorithms",
 code: "COMP9xxx",
 created_at: Mon, 05 Dec 2022 08:36:16.828535000 UTC +00:00,
 updated_at: Mon, 05 Dec 2022 08:38:13.160839000 UTC +00:00>
(rdbg) c # continue command
Completed 200 OK in 10259ms (Views: 0.5ms | ActiveRecord: 0.4ms | Allocations: 106092)
```

In a high-level overview, both byebug and ruby/debug are working similarly.

Debugging in Rails 7

Hit and evaluate