Pathfinder / Starfinder Assessment Evaluator

A static web app for calculating skill-challenge probabilities in Pathfinder 2e and Starfinder 2e, including exact degree-of-success shifts for nat-1 and nat-20.

Live at: apps.shadowfoot.com/pf2e-odds

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How it works

Enter a Task DC, optional modifiers, your Skill value, optional modifiers, and how many Successes needed. Results update on field change.

Outputs:

• Rolls projected to accumulate the required successes
• Fulfilment vs Breach probability within ceil(projected rolls), computed via a Markov chain
• Assessment breakdown: Critical Success / Success / Failure / Critical Failure per roll
• Nat-1 downgrade and nat-20 upgrade applied correctly per PF2e/SF2e rules

License

MIT — not published, endorsed, or specifically approved by Paizo Inc.