Background
Hookmark’s main function is to interact with other apps: opening items for you, serving links to their items, and creating new linked items. To do that, Hookmark communicates with those apps any way it is configured to (AppleScript, JavaScript, command line, x-callback-url.com, whatever).
Controlling Hookmark
It is also possible control Hookmark itself using programs you or others write, using Hookmark’s AppleScript dictionary. Hookmark’s dictionary will be described here. For now, please simply download Hookmark and check out its AppleScript dictionary.
You can also control Hookmark via a command line interface, which was created by Brett Terpstra.
Hookmark 2.0
Hookmark’s AppleScript dictionary was updated in Hookmark 2.0, published in November 2020: Changes to Hookmark’s AppleScript API coming in Hookmark 2.0 – Releases – Hookmark Forum. That page contains high level details for the AppleScript.