GTK-Doc is used to document C code. It is typically used to document the public API of libraries, such as the GTK+ and GNOME libraries, but it can also be used to document application code.

Note that GTK-Doc wasnt originally intended to be a general-purpose documentation tool, so it can be a bit awkward to setup and use. For a more polished general-purpose documentation tool you may want to look at Doxygen (http://www.doxygen.org/). However GTK-Doc has some special code to document the signals and properties of GTK+ widgets and GObject classes which other tools may not have.

GTK-Doc allows your documentation to be written in 2 ways:

a) Embedded inside the source code in specially-formatted comments.

or

b) Added to the template files which gtk-doc outputs after scanning all the header files and parsing the declarations.

From these source code comments and template files GTK-Doc generates a Docbook XML (or SGML) document, which is then transformed into HTML. The generated HTML documentation can be browsed in an ordinary web browser or by using the special Devhelp API browser (see http://developer.imendio.com/wiki/Devhelp).