Tools for Dyadic Multilevel Models // Provides tools for dyadic multilevel modeling with linear and generalized linear mixed- effects models. It validates and prepares long-format cross- sectional and intensive longitudinal data, including ecological momentary assessment designs, for distinguishable and exchangeable dyads. It also supports datasets containing multiple observed dyad compositions. It constructs composition- aware, model-ready variables for Actor-Partner Interdependence Models (APIMs), Dyadic Score Models (DSMs), and Dyad-Individual Models (DIMs). Prepared data can be used with model engines such as 'glmmTMB' and 'brms' for Gaussian and non-Gaussian outcomes, including counts, proportions, and skewed continuous responses. Post-estimation tools compare compatible fitted models and back-transform exchangeable sum-and-difference random-effect covariance structures into member-level quantities. The APIM and DSM specifications and their relationships follow Iida et al. (2018) doi:10.1177/0265407517725407; the multilevel sum-and-difference random-effects implementation for exchangeable dyads adapts del Rosario and West (2025) doi:10.1177/25152459251351286.