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Answer: "use server" marks a function or file to run on the server. Those Server Functions can be imported into Client Components; in mutation contexts they are Server Actions.

Directive

The use server directive designates a function or file to be executed on the server. All functions in a "use server" file run on the server.

Calling from the client

Create Server Functions in a dedicated file, then import them into Client Components to execute them.

Return values

Server Function return values are serialized and sent to the client. Return only what the UI needs.

See also

• nextjs-forms
• nextjs-revalidating

Claims

• id: C1 claim: use server runs code on the server. source: S1 evidence: "The use server directive designates a function or file to be executed on the **server"

• id: C2 claim: Import Server Functions into Client Components. source: S1 evidence: "To use Server Functions in Client Components you need to create your Server Functions in"

• id: C3 claim: Return values are serialized to the client. source: S1 evidence: "Server Function return values are serialized and sent to the client."

• id: C4 claim: Mutation context calls them Server Actions. source: S2 evidence: "In an action or mutation context, they are also called Server Actions."

Sources

• [S1] use server. Next.js docs. https://nextjs.org/docs/app/api-reference/directives/use-server . License: MIT (vercel/next.js). Accessed 2026-11-09.

• [S2] Mutating data. Next.js docs. https://nextjs.org/docs/app/getting-started/mutating-data . License: MIT (vercel/next.js). Accessed 2026-11-09.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted). Copyright (c) 2025 Vercel, Inc. Sources: Next.js docs (vercel/next.js on GitHub / nextjs.org), MIT (https://raw.githubusercontent.com/vercel/next.js/canary/license.md). Text was condensed and changed from the originals.

@misc{iil_note_khwcwmbs,
  author = {{iinventedlight}},
  title = {{The use server directive and Server Functions}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-09},
  url = {https://iinventedlight.com/library/notes/nextjs-use-server/},
  note = {Permanent ID iil:note:khwcwmbs. License: CC-BY-4.0.},
}

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