The developer of the system to be tested needs to provide some support (classes named "fixtures", conforming to certain conventions).

The program first supported only Java, but versions for several other languages have been added over time (C++, Python, Ruby, Delphi, C#, etc.).

The most generic form is a fully free-form table that can be interpreted in any way the test designers like.

Wikis classically allow for the easy and rapid creation of HTML pages and particularly simplify the expression of tables.

These qualities make the basic WikiWiki language an ideal choice for a "user interface" for FitNesse: on the one hand it allows for the simple expression of very free-form tables, on the other hand it limits the contents of those tables to rather simple text.

FitNesse is a tool developed in Java and shipped as a single, executable jar file.

As such it ships with all required components on board: upon execution the tool launches an embedded web server which allows test pages to be exposed locally or across the Internet with equal ease.

The default wiki created by the tool includes the FitNesse user guide and some examples.

The default document repository is created complete with everything needed to publish a default wiki in the FitNesse style (that is, all the images, stylesheets, JavaScript files and so on are created together with the basic wiki page repository).

FitNesse was originally built around Fit as a user interface, which inspired the name of the tool.

This can be inconvenient in Java, as it means that the framework claims a developer's one chance at class inheritance.

These considerations have prompted the FitNesse team in recent years to move to the SLIM testing engine.