Correctness

Every Correctness rule svelte-vitals runs.

Svelte 5 runes and lifecycle misuse: code that compiles but behaves wrong.

Rule	Severity	Summary
`correctness/orphan-effect`	🔴 critical	An $effect created outside component initialisation throws effect_orphan at runtime.
`correctness/orphan-lifecycle`	🔴 critical	onMount, getContext and friends called outside component initialisation throw lifecycle_outside_component at runtime.
`correctness/server-browser-global`	🔴 critical	window, document, localStorage accessed in module scope or a load/handler crash SSR with a ReferenceError.
`correctness/autoplay-muted`	🟡 warning	Browsers block autoplay with audio, and a blocked autoplay does not error, so a <video autoplay> without muted silently never starts playing for real visitors.
`correctness/base-path-navigation`	🟡 warning	A hardcoded root-relative link resolves against the domain root, not kit.paths.base, so under a base path it lands outside the app and 404s in production.
`correctness/checkable-bind-value`	🟡 warning	bind on a checkbox or radio input binds the DOM value property, which checkbox/radio interaction never changes, so the bound state silently never updates.
`correctness/each-index-key`	🟡 warning	Keying an {#each} block by its index gives items position-based identity, the same bug as no key, only masked.
`correctness/each-key`	🟡 warning	An {#each} block over dynamic data should have a key.
`correctness/effect-as-derived`	🟡 warning	Use $derived instead of an $effect that only assigns state.
`correctness/effect-as-onmount`	🟡 warning	An $effect that reads no reactive value belongs in an event handler, {@attach}, or onMount instead.
`correctness/instance-browser-global`	🟡 warning	A component’s instance script runs on the server during SSR, so window/document reads at its top level crash the render.
`correctness/nonreactive-builtin-state`	🟡 warning	A plain Map, Set, Date, URL, or URLSearchParams in $state is not proxied, so its mutations are invisible to reactivity and the UI silently stops updating.
`correctness/prop-mutation`	🟡 warning	Don’t mutate a prop from $props() unless it is declared $bindable.
`correctness/stale-prop-derivation`	🟡 warning	A value computed from a prop without $derived is evaluated once, so the UI silently stops tracking the parent.
`correctness/unmutated-state`	🔵 info	Use const (or $state.raw) for a $state that is never mutated.

See Configuration to change a rule’s severity or turn it off.