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

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Example

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,
    }),
  });

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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

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

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