Game Systems and Modules
What a system is
A system is a set of rules. It decides what a character sheet looks like, what its fields mean, how dice are rolled, and what content (spells, monsters, equipment) is available.
Purple Cat is deliberately system-agnostic: the platform knows about tokens, maps, and dice, and it asks the system about everything else. That is why the character sheet for one system looks nothing like another's.
What a module is
A module is the package that teaches Purple Cat something. Most modules are systems, but not all:
| Module | What it adds |
|---|---|
| System 8 | The System 8 rules, sheet, and content, sourced from its wiki |
| System 5 | The System 5 rules |
| D&D 5e | Both SRD editions (2014 and 2024), with spells, feats, species, backgrounds, and monsters |
| Assets | A pack of reusable art |
| GenAI | AI-assisted generation features |
| Scenes | ‹verify — scene tooling› |
Modules are versioned against the platform's Module API, so a module states which platform versions it works with.
Choosing a system
Set the game system on the campaign. New characters in that campaign default to it. Changing a campaign's system after characters exist is disruptive — the sheet sections change, and content bound to the old system may not map onto the new one.
The built-in custom system is a no-rules sheet: named properties and nothing else. It is the right choice for a system Purple Cat does not support yet.
Enabling and disabling modules
Which modules are active is a per-user preference, in Settings. Disabling a module you do not use makes the app load a little less.
If a character's system module is disabled or fails to load, its sheet will say so rather than silently rendering wrong values.
System reference material
Systems can bring their own reference wiki, shown in a sidebar next to the game. System 8 and System 5 both do.
Writing your own
The Module API is public and documented for developers.