Quest Journal Search tells you which mod added that unfamiliar quest

Image credit: Quest Journal Search by DeanKage via Nexus Mods.
After enough hours in a heavily modded Skyrim, even finding the quest you meant to finish can become a chore. DeanKage's Quest Journal Search adds a searchable overlay for titles and objectives, including the plugin responsible for each entry. That makes it easier to track down both a forgotten quest and the mod that put it there.
The tool filters quest states and can track, untrack or hide entries without replacing the game's journal interface. It supports specific Steam runtimes, including 1.5.97 and 1.7.104, and is designed for keyboard and mouse. Optional stage editing is a testing feature, not a way to undo everything a quest has already changed in the world.





