gtk-doc-tools software package provides GTK+ documentation tools, you can install in your Debian 8 (Jessie) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gtk-doc-tools
gtk-doc-tools is installed in your system.
Make ensure the gtk-doc-tools package were installed using the commands given below,
$ sudo dpkg-query -l | grep gtk-doc-tools *
You will get with gtk-doc-tools package name, version, architecture and description in a table
| Distro | Debian 8 jessie |
| Section | GNOME |
| Package | gtk-doc-tools |
| Version | 1.21-2 |
| Description | GTK+ documentation tools |
| Sub Section | GNOME |