diff --git a/packages/core-realtime/package.json b/packages/core-realtime/package.json
index 17194e9..4d01694 100644
--- a/packages/core-realtime/package.json
+++ b/packages/core-realtime/package.json
@@ -24,6 +24,7 @@
   },
   "devDependencies": {
     "@repo/core-eslint": "workspace:*",
+    "@repo/core-testing": "workspace:*",
     "@repo/core-typescript": "workspace:*",
     "@types/node": "^22.0.0",
     "typescript": "^5.8.0",
diff --git a/packages/core-realtime/src/realtime-channel.test.ts b/packages/core-realtime/src/realtime-channel.test.ts
new file mode 100644
index 0000000..357e732
--- /dev/null
+++ b/packages/core-realtime/src/realtime-channel.test.ts
@@ -0,0 +1,25 @@
+import { describe, it, expect } from "vitest";
+import { z } from "zod";
+import { defineRealtimeChannel } from "@/realtime-channel";
+
+describe("defineRealtimeChannel", () => {
+  it("returns a descriptor with name, schema, and scope", () => {
+    const ch = defineRealtimeChannel(
+      "test.channel",
+      z.object({ id: z.string() }).strict(),
+      { scope: "public" },
+    );
+    expect(ch.name).toBe("test.channel");
+    expect(ch.scope).toBe("public");
+    expect(() => ch.schema.parse({ id: "x" })).not.toThrow();
+  });
+
+  it("preserves all four scope shapes", () => {
+    expect(defineRealtimeChannel("a", z.object({}), { scope: "public" }).scope).toBe("public");
+    expect(defineRealtimeChannel("a", z.object({}), { scope: "authenticated" }).scope).toBe("authenticated");
+    expect(defineRealtimeChannel("a", z.object({}), { scope: { role: "admin" } }).scope).toEqual({ role: "admin" });
+    expect(
+      defineRealtimeChannel("a", z.object({}), { scope: { userScoped: true, template: "x.{id}" } }).scope,
+    ).toEqual({ userScoped: true, template: "x.{id}" });
+  });
+});
diff --git a/packages/core-realtime/src/realtime-channel.ts b/packages/core-realtime/src/realtime-channel.ts
new file mode 100644
index 0000000..3aeeede
--- /dev/null
+++ b/packages/core-realtime/src/realtime-channel.ts
@@ -0,0 +1,21 @@
+import type { z } from "zod";
+
+export type ChannelScope =
+  | "public"
+  | "authenticated"
+  | { role: string }
+  | { userScoped: true; template: string };
+
+export type RealtimeChannelDescriptor<TName extends string, TSchema extends z.ZodType> = {
+  readonly name: TName;
+  readonly schema: TSchema;
+  readonly scope: ChannelScope;
+};
+
+export function defineRealtimeChannel<TName extends string, TSchema extends z.ZodType>(
+  name: TName,
+  schema: TSchema,
+  options: { scope: ChannelScope },
+): RealtimeChannelDescriptor<TName, TSchema> {
+  return { name, schema, scope: options.scope };
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index ca10382..999c0e2 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -571,6 +571,9 @@ importers:
       '@repo/core-eslint':
         specifier: workspace:*
         version: link:../core-eslint
+      '@repo/core-testing':
+        specifier: workspace:*
+        version: link:../core-testing
       '@repo/core-typescript':
         specifier: workspace:*
         version: link:../core-typescript