diff --git a/data/api/client-server/definitions/event_filter.yaml b/data/api/client-server/definitions/event_filter.yaml
index ceb0d5bf..ad91e699 100644
--- a/data/api/client-server/definitions/event_filter.yaml
+++ b/data/api/client-server/definitions/event_filter.yaml
@@ -26,6 +26,8 @@ properties:
       `senders` filter.
     items:
       type: string
+      format: mx-user-id
+      pattern: "^@"
     type: array
   not_types:
     description: A list of event types to exclude. If this list is absent then no
@@ -40,6 +42,8 @@ properties:
       senders are included.
     items:
       type: string
+      format: mx-user-id
+      pattern: "^@"
     type: array
   types:
     description: A list of event types to include. If this list is absent then all
diff --git a/data/api/client-server/definitions/room_event_filter.yaml b/data/api/client-server/definitions/room_event_filter.yaml
index 6c9b705d..de908a82 100644
--- a/data/api/client-server/definitions/room_event_filter.yaml
+++ b/data/api/client-server/definitions/room_event_filter.yaml
@@ -43,12 +43,16 @@ allOf:
         filter.
       items:
         type: string
+        format: mx-room-id
+        pattern: "^!"
       type: array
     rooms:
       description: A list of room IDs to include. If this list is absent then all rooms
         are included.
       items:
         type: string
+        format: mx-room-id
+        pattern: "^!"
       type: array
     contains_url:
       type: boolean
diff --git a/data/api/client-server/definitions/sync_filter.yaml b/data/api/client-server/definitions/sync_filter.yaml
index f181aa22..6f80b4c1 100644
--- a/data/api/client-server/definitions/sync_filter.yaml
+++ b/data/api/client-server/definitions/sync_filter.yaml
@@ -50,6 +50,8 @@ properties:
           `state`, `timeline` or `account_data`
         items:
           type: string
+          format: mx-room-id
+          pattern: "^!"
         type: array
       rooms:
         description: A list of room IDs to include. If this list is absent then all rooms
@@ -57,6 +59,8 @@ properties:
           `state`, `timeline` or `account_data`
         items:
           type: string
+          format: mx-room-id
+          pattern: "^!"
         type: array
       ephemeral:
         allOf:
diff --git a/data/api/client-server/filter.yaml b/data/api/client-server/filter.yaml
index f1135939..551748d4 100644
--- a/data/api/client-server/filter.yaml
+++ b/data/api/client-server/filter.yaml
@@ -36,6 +36,8 @@ paths:
           example: "@alice:example.com"
           schema:
             type: string
+            format: mx-user-id
+            pattern: "^@"
       requestBody:
         content:
           application/json:
@@ -130,6 +132,8 @@ paths:
           example: "@alice:example.com"
           schema:
             type: string
+            format: mx-user-id
+            pattern: "^@"
         - in: path
           name: filterId
           description: The filter ID to download.