PF2e / SF2e Odds Calculator

A single-page web app for calculating probabilities in Pathfinder 2e and Starfinder 2e skill challenges.

Features

• Inputs: Task DC, Task modifiers, Skill, Skill modifiers, Successes needed.
• Outputs:
  • DC and Skill Bonus badges (colour-coded).
  • Per-roll odds: Critical Success, Success, Failure, Critical Failure, and Any success.
  • Expected rolls (fractional, 1 dp).
  • Completion vs Catastrophe with a split bar.
• Exact PF2e/SF2e degree shifts (nat 1 downgrade, nat 20 upgrade).
• Markov model to compute catastrophe vs completion within ceil(expected rolls).
• Responsive dark theme; mobile-friendly; no dependencies.

Usage

1. Open https://ShadowfootNZ.github.io/pf2e-odds/ in a modern browser.
2. Enter Task and Skill values; set Successes needed.
3. Results update when you tab out of a field.

Development

• Pure HTML/CSS/JavaScript; no build step.
• Script is wrapped in DOMContentLoaded to avoid globals.

Folder structure

pf2e-odds/
├─ index.html        # main app
├─ README.md         # this file
└─ docs/             # optional assets
   └─ screenshot.png (optional)

License

MIT