Tips and tricks for snooping about your codebase with the Pry console. You'll learn how to view the source code of ANY method on demand, see global variables, or change "self" to another object.
Master the universal debugger commands "step" and "next" and learn how to crack open a Pry session at any point.
Unix/Command-Line level tools for making web-developers' lives easier– lsof, nslookup, gdb, tcpdump, ctags, ack, strace, and top
How Google Webmaster Tools, Google Search, New Relic, and email delivery reports can help you uncover errors in your web application
Many apps use Memcached in their infrastructure so it's important to know how to debug thorny caching errors.
Everything you ought to be looking at when interpreting the Rails built-in logs. Also looks at other logs, such as Amazon S3 access logs and scheduler logs.
Source control software gives us a unique insight into changes in code and the human intention behind them.
Why settle with the debugging tools built into Rails? Why not create your own custom tools to ease the load?
Chrome DevTools gives you yet another angle for debugging your software, especially the CSS and JS.
Lesser known tools built in to the standard stack - such as the middleware lister, Gemfile.lock, Ruby compiler checks, rails dbconsole
Feedback systems for finding errors in your web application.
The disadvantages of using Cucumber and its widespread use as a poor man's integration test.