There's a simple reason for this: keeping the core engine closed-source is a deliberate design philosophy choice, not an oversight.
To be completely transparent, Capsule V2 will already cover roughly 95% of the practical use cases for which creators typically rely on Python in Ren'Py, without requiring hours of coding. The engine is designed as a complete narrative solution rather than a general-purpose development framework.
That is also why there is currently no plugin API. I had two possible directions to choose from:
- Build a structured scripting and extension system with arbitrary code execution.
- Keep Capsule as a secure, self-contained engine with built-in systems and a template system that allows users to create and share gameplay frameworks without executing arbitrary code.
I chose the second approach.
Furthermore, Capsule games are built for ultimate portability and effortless deployment: everything resides within a single, standalone HTML file. While this single-file architecture makes distribution incredibly easy and friction-free for creators and players alike, it also exponentially magnifies the security stakes.
Allowing arbitrary script or plugin injection into a lightweight, web-based file would be a security nightmare. It opens the door to malicious code being executed directly within a player's browser or environment—a glaring vulnerability present in several popular visual novel workflows that shall remain nameless. While some developers prefer to wash their hands of the risk with a "user is responsible, we disclaim all liability" approach, that is simply not mine.
Capsule already includes most systems that typically require custom scripting in other engines anyway: variables and formulas, branching, inventory systems, quests, codex entries, maps, achievements, endings, events, hotspots, reusable animations, HUDs, QTEs, progression systems, and much more.
Capsule isn't trying to compete with Ren'Py's unlimited Python extensibility, Naninovel/Unity's ecosystem, or Dialogic/Godot's scripting capabilities. Those engines are excellent choices for teams that need deep programmability and custom integrations.
The goal of Capsule is different: to provide a highly capable, secure, and easy-to-use narrative engine that covers the vast majority of visual novel, narrative, and RPG needs right out of the box, without ever compromising the safety of the players.