Caught errors can be logged in human-readable form:

print-error ( error -- )

try ( quot -- )

User-defined errors can have customized printed representation by implementing a generic word:

error. ( error -- )

A number of words facilitate interactive debugging of errors:

:error ( -- )

:s ( -- )

:r ( -- )

:c ( -- )

:get ( variable -- value )

Most types of errors are documented, and the documentation is instantly accessible:

:help ( -- )

If the error was restartable, a list of restarts is also printed, and a numbered restart can be invoked:

:1 ( -- * )

:2 ( -- * )

:3 ( -- * )

:res ( n -- * )

You can read more about error handling in Exception handling.

Note that in Factor, the debugger is a tool for printing and inspecting errors, not for walking through code. For the latter, see UI walker.