What it uses: your answers to nine questions (age, fitness, medical history, gear, experience, tool and navigation skills, survival, team readiness, guide), your body weight, pack weight and pace, and each trail's track data: the time it takes for your body and pack, distance, total gain, summit elevation and steepness. All five are rated on the same 1–5 scale as difficulty.
Before ranking, some trails can be hidden by Safety limits; for example, a serious medical history opens only the easiest trails. Hidden trails are always named on the result, with the reason.
What it ignores: weather and season, reviews or popularity, whether a trail is open or closed, permits and fees, and how far the trail is from where you live. Trails with incomplete track data are not guessed; they are listed as not assessed.
Recommendation is a ranking of fit from your own answers, not a medical assessment or a guarantee of safety. Check trail conditions and the forecast, and listen to your body before you hike.