Heads up! This blog post hasn't been updated in over 2 years. CodePen is an ever changing place, so if this post references features, you're probably better off checking the docs. Get in touch with support if you have further questions.

Running JS Hint in your Pens just got a lot more useful! We now display the error messages right inline in the editor so it's very easy to see the issues and fix them.

inline-jshint-errors

The errors appear directly below the line that caused the "error."

Press Command-Shift-7 to run (or re-run) JS Hint.
Press Command-Shift-8 to hide the messages.

(Control instead of Command on PC's)

We provide links to Google the errors in case you need help fixing them. There is some similarities between JS Hint and JS Lint as well, so this might be useful.

Our plan is to provide more inline messaging over time, eventually moving over preprocessor errors, validation, and more.