Surrogate Evaluation for Jointly Longitudinal Outcome and Surrogate R package OnlineSurr version 0.0.3 Tools for surrogate evaluation in longitudinal studies using state-space models. The package estimates treatment effects over time with and without adjustment for surrogate information, summarizes the proportion of treatment effect explained by a longitudinal surrogate, quantifies uncertainty via bootstrap resampling, and provides plotting and summary utilities for fitted models. Software Depends: R (>= 4.1.0) Imports: kDGLM (>= 1.2.14), dplyr, ggplot2, tidyr, rlang, Rfast, stats, latex2exp, Rdpack Suggests: knitr, rmarkdown Silvaneo dos Santos Jr. <silvaneojunior@utexas.edu> Comprehensive R Archive Network (CRAN) Silvaneo dos Santos Jr. [aut, cre], Layla Parast [aut] GPL (>= 3) 2026-04-21 application/tgz https://CRAN.R-project.org/package=OnlineSurr doi:10.32614/CRAN.package.OnlineSurr