diff --git a/packages/api/src/__tests__/comment-entity-registry.test.ts b/packages/api/src/__tests__/comment-entity-registry.test.ts
new file mode 100644
index 0000000..2d390e9
--- /dev/null
+++ b/packages/api/src/__tests__/comment-entity-registry.test.ts
@@ -0,0 +1,17 @@
+import { describe, expect, it } from "vitest";
+import {
+  CommentEntityTypeSchema,
+  getCommentToolEntityDescription,
+  getCommentToolScopeSentence,
+  getSupportedCommentEntityTypes,
+} from "../lib/comment-entity-registry.js";
+
+describe("comment entity registry metadata", () => {
+  it("keeps the router schema and helper metadata aligned", () => {
+    expect(getSupportedCommentEntityTypes()).toEqual(["estimate", "resource"]);
+    expect(CommentEntityTypeSchema.options).toEqual(["estimate", "resource"]);
+    expect(getCommentToolEntityDescription()).toContain("estimate, resource");
+    expect(getCommentToolScopeSentence()).toContain("Supported comment entities: estimate, resource.");
+    expect(getCommentToolScopeSentence()).toContain("resource comments follow resource detail visibility");
+  });
+});
diff --git a/packages/shared/src/constants/comment-entities.ts b/packages/shared/src/constants/comment-entities.ts
new file mode 100644
index 0000000..76ffe5e
--- /dev/null
+++ b/packages/shared/src/constants/comment-entities.ts
@@ -0,0 +1,8 @@
+export const COMMENT_ENTITY_TYPE_VALUES = ["estimate", "resource"] as const;
+
+export type CommentEntityType = (typeof COMMENT_ENTITY_TYPE_VALUES)[number];
+
+export const COMMENT_ENTITY_LABELS: Record<CommentEntityType, string> = {
+  estimate: "estimate",
+  resource: "resource",
+};