Advanced Package Tool (APT) is a free-software user interface that works with core libraries to handle the installation and removal of software on Debian and Debian-based Linux distributions.

APT provides other command options to override decisions made by apt-get's conflict resolution system.

This can downgrade a package and render dependent software inoperable, so the user must be careful.

Finally, the apt_preferences mechanism allows the user to create an alternative installation policy for individual packages.

[13] APT relies on the concept of repositories in order to find software and resolve dependencies.

As of 14 August 2021,[update] the Debian project keeps a central repository of over 50,000 software packages ready for download and installation.

Several other front ends to APT exist, which provide more advanced installation functions and more intuitive interfaces.

The original effort that led to the apt-get program was the dselect replacement project known by its codename Deity.

[25] Much of the original development of APT was done on Internet relay chat (IRC), so records have been lost.

[27] In the end the original goal of the Deity project of replacing the dselect user interface was a failure.

The response to APT as a dselect method and a command line utility was so great and positive that all development efforts focused on maintaining and improving the tool.

Eventually, a new team picked up the project, began to build new features and released version 0.6 of APT which introduced the Secure APT feature, using strong cryptographic signing to authenticate the package repositories.

[28] APT was originally designed as a front end for dpkg to work with Debian's .deb packages.

A version of APT modified to also work with the RPM Package Manager system was released as APT-RPM.