Shiny apps

Shiny bugs rarely show up as syntax errors. They show up as outputs that never update, observers that fire twice, or inputs that reset when they should not. Generic assistants struggle because they treat Shiny like any other web framework.

Shiny debug mode

Paste your ui.R and server.R (or single-file app). RCode traces reactive dependencies, flags invalidation loops, and suggests minimal fixes — often a missing reactiveVal or an observer that should be a reactive expression.

Common fixes

• Reactive graph not updating when a filter changes
• DT datatable losing selection on re-render
• Module namespace mistakes in nested components
• Performance: too many reactives recomputing on every keystroke