> ## Documentation Index
> Fetch the complete documentation index at: https://redop.useagents.site/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Add Request Context with derive

> Use derive to attach reusable request data to ctx before hooks, middleware, and handlers run.

Use `derive(...)` when several tools need the same request-derived state.

## Example

```ts theme={null}
import { Redop } from "@redopjs/redop";

const app = new Redop()
  .derive(async ({ request }) => ({
    authHeader: request.headers.authorization ?? null,
    tenantId: request.headers["x-tenant-id"] ?? "public",
  }))
  .tool("whoami", {
    handler: ({ ctx }) => ({
      authHeader: ctx.authHeader,
      tenantId: ctx.tenantId,
    }),
  });
```

## When to use it

* auth metadata shared across many tools
* tenant or account selection from headers
* request-scoped utilities you do not want to recalculate in every handler

## Why use `derive(...)` instead of middleware?

Use `derive(...)` when you want to enrich `ctx`. Use middleware when you need to control execution flow.