Day 1 $inspect.trace()
Like Santa checking his list twice, $inspect.trace() helps you see exactly which pieces of reactive state caused your effects to re-run.
Added in Svelte 5.14, place this rune as the first statement inside any $effect or $derived to get detailed console output about what's naughty (triggering unnecessary updates) and what's nice (working as expected).
You can even pass an optional label to help identify your traces — because even Santa needs good logging when managing millions of deliveries!