server-actions

Export an async function from a module with "use server" at the top, or declare an inline action inside a server component with the directive in the function body. File-level actions are preferred for reuse and support path-based revalidation matching.

Return structured errors from the action as state instead of throwing, using the (prevState, formData) signature. Re-render the form with defaultValue from state.values so user input survives validation failures, and display errors per field.

Use server actions for writes and mutations, and loaders for reads. Actions mutate state and trigger revalidation of matched route segments, while loaders fetch live data on navigation or on demand from the client.

No, route-level middleware() does not wrap action execution since actions run before route middleware. Place authorization checks in global router.use() middleware or inside the action body itself.

redirect() is same-origin by default, so cross-origin targets are blocked and the user is sent to the app root. Pass { external: true } to intentionally redirect off-host, and note the target must still be an http(s) URL.

Yes, <form action={serverAction}> submits as a normal HTTP POST when JavaScript is unavailable, the action runs server-side, and the page re-renders. Write actions that accept FormData directly rather than curried or client-wrapped functions.