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OSR+ is designed to accommodate an ever-expanding library of content such as new spells, treasures, archetypes, kits, classes, and origins. In this section, we'll discuss the design principles that go into each type of content, and how to homebrew the above without breaking the rules.

On Armament & Skills

Some content in OSR+ is not meant to be expanded upon. For example, there is no need to add new skills to the system, because for the fantasy core rules, the existing skills are designed to cover all possible categories of skill imaginable. Adding new ones unnecessarily will throw off the balance of the system. The same is true of weapon and armor classes, tactics, ethos, and maleficence.

Weapon types are purely stylistic, however, so adding new types doesn't matter mechanically. While there's definitely a meaningful difference in real life between a katar and a stiletto, in OSR+ they're both reducible to Small weapons, which do the same amount of damage and carry the same tactic.

Designing Homebrew Content


Be sure to consult the core rules on spell logic when designing a new spell. A spell should be no more than a paragraph long. Here are some things to consider when designing the spell.

Origins, Classes, Kits

The relative power of the abilities granted by origins, classes, and kits ranks in that order. Here are tips for creating homebrew in these categories.


Archetypes are optional and define the narrative role a character fills in the game. Each world of OSR+ introduces a handful of archetypes unique to that world to give the players clear examples of how their characters can fit into the general feel of the setting. When creating homebrew archetypes, consider how they expand your campaign setting.


Treasures are declared supply that impart special abilities when characters use them. Don't lose sight of their wondrous qualities when creating homebrew treasures.

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