server-only is a utility package that marks modules as server-side only in Node.js. This helps prevent accidental client-side exposure of sensitive data or server-specific logic when using bundlers like Webpack or esbuild. By importing server-only, you signal to build tools that the module should only be included within a server environment, providing an extra layer of security and reducing client-side bundle size. It enhances application security and optimizes performance by clearly defining the execution context.