Most AI tools answer a probability question with a single confident paragraph. Probability Lab treats that as malpractice. The final number is the end of a visible construction: it starts from historical base rates, is rebuilt from causally distinct scenarios that each survive an adversarial debate, and is then deliberately corrected for the failure modes that inflate naive forecasts — overlapping stories, elegant narratives, crowded optimism, and paths that cannot complete inside the time window.
Every run ends with an executive layer (the number, its uncertainty band, a direct answer, what would move it) and a construction layer (the correction waterfall, scenario contributions, full debate transcripts, factor crosswalks). Busy readers stop at the first; skeptical readers can audit the second.
Defended forecastThe headline probability with a verdict label — from “remote” to “highly likely”.
Uncertainty bandA Monte Carlo p10–p90 range propagated from the judges' stated intervals, not a decorative ±5%.
Why this numberWhy it isn't higher, why it isn't lower, and which assumptions the forecast leans on hardest.
What would move itConcrete swing factors and observable tripwires, with timing.