A class browser is a feature of an integrated development environment (IDE) that allows the programmer to browse, navigate, or visualize the structure of object-oriented programming code.
Most modern class browsers owe their origins to Smalltalk, one of the earliest object-oriented languages and development environments.
Continuing the Smalltalk tradition, columnar browsers display the class hierarchy from left to right in a series of columns.
Systems with roots in Microsoft Windows tend to use an outline-form browser, often with colorful (if cryptic) icons to denote classes and their attributes.
This is somewhat like editing JavaScript prototypes in a web browser or Ruby, Groovy or Jython classes in an IDE running in a JVM.