The Administrator Reference Manual (ARM) for Kea is the authoritative reference for Kea commands and usage. The Kea ARM and the Kea Messages Guide are available in both .html and .pdf formats via ISC's downloads site at https://downloads.isc.org/isc/kea or, for Kea version 1.6.0 and later, via Read the Docs.
The Kea Messages Guide
The Kea Developer Guide
The Kea Developer Guide is intended for existing or prospective Kea developers and contributors, and provides information needed to extend and maintain Kea source code. This guide is a living document for the current development version.
If you wish to write hooks code - the code that is loaded by Kea at run-time and modifies its behavior - you should read the Hooks Developer's Guide section.