Search params are not available in layouts in Next.js App Router for a specific reason related to performance and rendering behavior. Let me explain:

1. Layouts in Next.js App Router are not re-rendered during navigation . This is an intentional design choice to optimize performance.
2. When using client-side navigation, Next.js automatically only renders the part of the page below the common layout between two routes 1. This partial rendering approach significantly improves navigation speed.
3. Because layouts are not re-rendered during navigation, if they were to receive searchParams, these params could become stale after navigation 1. This could lead to inconsistent or outdated information being displayed in the layout.

To illustrate this, consider a scenario where you have a shared layout for multiple pages within a dashboard:

When navigating from /dashboard/settings to /dashboard/analytics, only the page.tsx in /dashboard/analytics will re-render. The layout.tsx in /dashboard will not re-render because it's shared between these routes 1.

Instead of using searchParams in layouts, you have two main alternatives:

1. Use the Page searchParams prop: This is available in your page components and will always have the most up-to-date values .
2. Use the useSearchParams hook: This is a Client Component hook that will re-render on the client with the latest searchParams .

By using these alternatives, you ensure that your components always have access to the most current search parameters, maintaining consistency in your application's state.