PHQ-9
Strong evidenceFree · scored onlineFree · items + scoring keyDepression symptom severity over the past two weeks · 9 items · ~2 min
The standard depression screen in primary care worldwide, released by Pfizer with no permission required, which is part of why it's everywhere. Severity bands at 5, 10, 15, and 20 are well validated, and it's designed for re-taking to track change. Fair warning: item 9 asks directly about thoughts of self-harm.