Turns wave-and-respondent selection in longitudinal panel and repeated-measures data into an explicit, reproducible workflow. Provides a scope-based pipeline for wave pattern analysis and a planning interface for scenario-based respondent selection with configurable missing-wave tolerances, interior-gap constraints, and endpoint requirements. Wave grids may be consecutive integers or the observed schedule (e.g. biennial panels). Includes tolerance-sensitivity and attrition-selectivity diagnostics, plus a generator of ready-to-paste methods-section justification text. A full workflow guide is available at < https://siardv.github.io/weasel/>.