diff --git a/lib/types/relationship-types.js b/lib/types/relationship-types.js
--- a/lib/types/relationship-types.js
+++ b/lib/types/relationship-types.js
@@ -1,10 +1,11 @@
 // @flow
 
-import type { TRefinement } from 'tcomb';
+import type { TInterface, TRefinement } from 'tcomb';
+import t from 'tcomb';
 
 import type { AccountUserInfo } from './user-types.js';
 import { values } from '../utils/objects.js';
-import { tNumEnum } from '../utils/validation-utils.js';
+import { tNumEnum, tShape, tString } from '../utils/validation-utils.js';
 
 export const undirectedStatus = Object.freeze({
   KNOW_OF: 0,
@@ -67,10 +68,26 @@
 export type RelationshipButton = $Values<typeof relationshipButtons>;
 
 export type RelationshipRequest = {
-  action: RelationshipAction,
-  userIDs: $ReadOnlyArray<string>,
+  +action: RelationshipAction,
+  +userIDs: $ReadOnlyArray<string>,
 };
 
+export type FarcasterRelationshipRequest = {
+  +action: 'farcaster',
+  +userIDsToFID: { +[userID: string]: string },
+};
+
+const exactlyTwoDictEntriesValidator = t.refinement(
+  t.dict(t.String, t.String),
+  dict => Object.keys(dict).length === 2,
+);
+
+export const updateFarcasterRelationshipInputValidator: TInterface<FarcasterRelationshipRequest> =
+  tShape<FarcasterRelationshipRequest>({
+    action: tString('farcaster'),
+    userIDsToFID: exactlyTwoDictEntriesValidator,
+  });
+
 type SharedRelationshipRow = {
   user1: string,
   user2: string,
diff --git a/lib/types/relationship-types.test.js b/lib/types/relationship-types.test.js
new file mode 100644
--- /dev/null
+++ b/lib/types/relationship-types.test.js
@@ -0,0 +1,49 @@
+// @flow
+
+import { updateFarcasterRelationshipInputValidator } from './relationship-types.js';
+
+describe('updateFarcasterRelationshipInputValidator', () => {
+  test('SHOULD validate input with exactly 2 userIDsToFID entries', () => {
+    const input = {
+      action: 'farcaster',
+      userIDsToFID: {
+        '256': 'f256',
+        '512': 'f512',
+      },
+    };
+    expect(updateFarcasterRelationshipInputValidator.is(input)).toBe(true);
+  });
+
+  test('SHOULD NOT validate input with > 2 userIDsToFID entries', () => {
+    const input = {
+      action: 'farcaster',
+      userIDsToFID: {
+        '256': 'f256',
+        '512': 'f512',
+        '1024': 'f1024',
+      },
+    };
+    expect(updateFarcasterRelationshipInputValidator.is(input)).toBe(false);
+  });
+
+  test('SHOULD NOT validate input with < 2 userIDsToFID entries', () => {
+    const input = {
+      action: 'farcaster',
+      userIDsToFID: {
+        '256': 'f256',
+      },
+    };
+    expect(updateFarcasterRelationshipInputValidator.is(input)).toBe(false);
+  });
+
+  test('Should not validate if action is not farcaster', () => {
+    const input = {
+      action: 'NOT_FARCASTER',
+      userIDsToFID: {
+        '256': 'f256',
+        '512': 'f512',
+      },
+    };
+    expect(updateFarcasterRelationshipInputValidator.is(input)).toBe(false);
+  });
+});