5 Mistakes That Slow Down Your Flutter App

Most Flutter apps are fast until they are not. These are the five causes I find most often when profiling a janky build.

1. Rebuilding whole subtrees — a setState high in the tree repaints everything below it. Push the stateful widget down.
2. shrinkWrap: true inside a scroll view — this quietly measures every child on every frame.
3. Unbounded ListView(children: [...]) — use ListView.builder and build lazily.
4. Decoding JSON on the UI isolate — move it to a background isolate with compute.
5. Images at full resolution — a 4000px photo in a 200px slot costs memory and decode time every frame.

Fix the first one and you usually fix half the jank.