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Retroactive Skill Books

This mod allows you to regain XP you missed out on by training skills while you hadn't yet read a skill book. I like Project Zomboid's approach to skill books, but don't like how strict it can feel--feeling like I should drop everything to go read the next skill book immediately upon leveling. It also feels realistic to me that your character would remember recent experiences and could reflect on and grow from those as they read a skill book. So, I decided to make this mod for my own playthroughs.


Whenever a player gains XP, this mod stores the difference in XP earned and the XP that could have been earned if the current skill book was fully read, taking into account any multipliers from partially read skill books. When a player finishes reading a skill book, this mod checks for stored XP for that skill book level and gives that XP back to the player, scaled by a factor that can be adjusted in sandbox options. The XP returned is also capped to the maximum trainable skill level of that skill book by default, but this can also be adjusted in sandbox options if you want an even more lenient system.

This mod now also optionally will return missed XP from obsolete skill books, or skill books the player has leveled beyond. The player character will comment differently when reading an obsolete skill book with available XP to be returned. For now, this XP can be returned in full or capped. In full means a player receives all (or most) of the missed XP from the trainable level range, which can be quite a lot. At max, this is the total XP needed to level times one less than the maximum multiplier. Capped means the player can receive, at most, what could have been returned before leveling out of the trainable range, or the max full XP divided by the maximum multiplier.


Any mod that grants un-boosted XP would result in the player gaining extra XP when reading a skill book.

Mods that add new skill books should work fine. At worst, you may not receive retroactive XP, but even that should work. However, if a mod somehow changes the trainable levels of skill books, this mod will no longer work correctly.

Obviously, any mod balanced around the vanilla XP and skill book system or that overhauls the skill book system may be disrupted by this mod.

Now includes an option to pause XP tracking to help compatibility with mods that grant XP for reading skill books.

You should be able to add this mod to existing saves with no issues, but XP earned before this mod was activated will not be stored.


I'm a very amateur modder and this mod was only minimally tested in a locally hosted server, so I can't guarantee it will work in multiplayer.


Possible bug that returns too much XP for reading a vol. 5 skill book.

Possible bug with the option to pause XP tracking, resulting in XP return from mods that grant XP for reading skill books.

Currently, XP that levels you out of a trainable skill range will not be counted as missed XP for the purposes of returning XP from an obsoleted skill book.

Workshop ID: 2908032114
Mod ID: JSRetroBooks