Debugging in Ruby 2

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Debugging in Ruby 2

Byebug is a simple to use, feature rich debugger for Ruby 2. It uses the new TracePoint API for execution control and the new Debug Inspector API for call stack navigation, so it doesn't depend on internal core sources. It's developed as a C extension, so it's fast. And it has a full test suite so it's reliable.

It allows you to see what is going on inside a Ruby program while it executes and offers many of the traditional debugging features such as:

  • Stepping: Running your program one line at a time.
  • Breaking: Pausing the program at some event or specified instruction, to examine the current state.
  • Evaluating: Basic REPL functionality, although pry does a better job at that.
  • Tracking: Keeping track of the different values of your variables or the different lines executed by your program.

Build Status

Linux & OSX Tra

Windows Vey


  • Required: MRI 2.0.0 or higher. For debugging ruby 1.9.3 or older, use debugger.

  • Recommended:

    • MRI 2.0.0-p576 or higher.
    • MRI 2.1.3 or higher.
    • MRI 2.2.0 or higher.


$ gem install byebug


Simply drop


wherever you want to start debugging and the execution will stop there. If you are debugging rails, start the server and once the execution gets to your byebug command you will get a debugging prompt.

Former debugger or ruby-debug users, notice:

  • Some gems (rails, rspec) implement debugging flags (-d, --debugger) that early require and start the debugger. These flags are a performance penalty and byebug doesn't need them anymore so my recommendation is not to use them. In any case, both rails and rspec have deprecated these flags in their latest versions.
  • The startup configuration file is now called .byebugrc instead of .rdebugrc.

Byebug's commands

Command     | Aliases      | Subcommands
----------- |:------------ |:-----------
`backtrace` | `bt` `where` |
`break`     |              |
`catch`     |              |
`condition` |              |
`continue`  |              |
`delete`    |              |
`disable`   |              | `breakpoints` `display`
`display`   |              |
`down`      |              |
`edit`      |              |
`enable`    |              | `breakpoints` `display`
`finish`    |              |
`frame`     |              |
`help`      |              |
`history`   |              |
`info`      |              | `args` `breakpoints` `catch` `display` `file` `files` `line` `program`
`irb`       |              |
`kill`      |              |
`list`      |              |
`method`    |              | `instance`
`next`      |              |
`p`         | `eval`       |
`pp`        |              |
`pry`       |              |
`ps`        |              |
`putl`      |              |
`quit`      | `exit`       |
`restart`   |              |
`save`      |              |
`set`       |              | `autoeval` `autoirb` `autolist` `autosave` `basename` `callstyle` `fullpath` `histfile` `histsize` `linetrace` `listsize` `post_mortem` `stack_on_error` `verbose` `width`
`show`      |              | `autoeval` `autoirb` `autolist` `autosave` `basename` `callstyle` `fullpath` `histfile` `histsize` `linetrace` `listsize` `post_mortem` `stack_on_error` `verbose` `width`
`source`    |              |
`step`      |              |
`thread`    |              | `current` `list` `resume` `stop` `switch`
`tracevar`  |              |
`undisplay` |              |
`up`        |              |
`var`       |              | `all` `constant` `global` `instance` `local`

Semantic Versioning

Byebug tries to follow semantic versioning and tries to bump major version only when backwards incompatible changes are released. Backwards compatibility is targeted to pry-byebug and any other plugins relying on byebug.

Getting Started

Read byebug's markdown guide to get started. Proper documentation will be eventually written.

Related projects


See Getting Started with Development.


Everybody who has ever contributed to this forked and reforked piece of software, specially:

  • @ko1, author of the awesome TracePoint API for Ruby.
  • @cldwalker, debugger's mantainer.
  • @denofevil, author of debase, the starting point of this.
  • @kevjames3 for testing, bug reports and the interest in the project.
  • @FooBarWidget for working and helping with remote debugging.
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