diff --git a/data/api/client-server/definitions/client_event.yaml b/data/api/client-server/definitions/client_event.yaml
index d9606676..88b0b96f 100644
--- a/data/api/client-server/definitions/client_event.yaml
+++ b/data/api/client-server/definitions/client_event.yaml
@@ -24,8 +24,9 @@ allOf:
       room_id:
         description: The ID of the room associated with this event.
         type: string
+        format: mx-room-id
+        pattern: "^!"
         example: '!jEsUZKDJdhlrceRyVU:example.org'
-
       unsigned:
         properties:
             redacted_because:
@@ -43,6 +44,6 @@ allOf:
                 "unsigned": {
                   "age": 1257,
                 }
-            }
+              }
     required:
       - room_id
diff --git a/data/api/client-server/definitions/client_event_without_room_id.yaml b/data/api/client-server/definitions/client_event_without_room_id.yaml
index b12611a2..fcdf32ea 100644
--- a/data/api/client-server/definitions/client_event_without_room_id.yaml
+++ b/data/api/client-server/definitions/client_event_without_room_id.yaml
@@ -28,6 +28,8 @@ properties:
   event_id:
     description: The globally unique identifier for this event.
     type: string
+    format: mx-event-id
+    pattern: "^\\$"
     example: '$26RqwJMLw-yds1GAH_QxjHRC1Da9oasK0e5VLnck_45'
   type:
     description: The type of the event.
@@ -47,6 +49,8 @@ properties:
   sender:
     description: Contains the fully-qualified ID of the user who sent this event.
     type: string
+    format: mx-user-id
+    pattern: "^@"
     example: "@example:example.org"
   origin_server_ts:
     description: |-
diff --git a/data/api/client-server/definitions/m.relates_to.yaml b/data/api/client-server/definitions/m.relates_to.yaml
index 401c8bb9..e1259c02 100644
--- a/data/api/client-server/definitions/m.relates_to.yaml
+++ b/data/api/client-server/definitions/m.relates_to.yaml
@@ -39,5 +39,7 @@ properties:
       such.
   event_id:
     type: string
+    format: mx-event-id
+    pattern: "^\\$"
     description: The event ID of the event that this event relates to.
 required: ['rel_type', 'event_id']
diff --git a/data/api/client-server/message_pagination.yaml b/data/api/client-server/message_pagination.yaml
index 4d5c94e1..c26f461d 100644
--- a/data/api/client-server/message_pagination.yaml
+++ b/data/api/client-server/message_pagination.yaml
@@ -37,6 +37,8 @@ paths:
           example: "!636q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
         - in: query
           name: from
           x-changedInMatrixVersion:
diff --git a/data/api/client-server/old_sync.yaml b/data/api/client-server/old_sync.yaml
index 1f97341a..b07c73f1 100644
--- a/data/api/client-server/old_sync.yaml
+++ b/data/api/client-server/old_sync.yaml
@@ -148,6 +148,8 @@ paths:
                       properties:
                         room_id:
                           type: string
+                          format: mx-room-id
+                          pattern: "^!"
                           description: The ID of this room.
                         membership:
                           type: string
@@ -337,6 +339,8 @@ paths:
           example: $asfDuShaf7Gafaw:matrix.org
           schema:
             type: string
+            format: mx-event-id
+            pattern: "^\\$"
       responses:
         "200":
           description: The full event.
diff --git a/data/api/client-server/redaction.yaml b/data/api/client-server/redaction.yaml
index 53f45bc5..0e9ff7f9 100644
--- a/data/api/client-server/redaction.yaml
+++ b/data/api/client-server/redaction.yaml
@@ -43,13 +43,17 @@ paths:
           example: "!637q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
         - in: path
           name: eventId
-          description: The ID of the event to redact
+          description: The ID of the event to redact.
           required: true
-          example: bai2b1i9:matrix.org
+          example: $bai2b1i9:matrix.org
           schema:
             type: string
+            format: mx-event-id
+            pattern: "^\\$"
         - in: path
           name: txnId
           description: |-
@@ -82,6 +86,8 @@ paths:
                 properties:
                   event_id:
                     type: string
+                    format: mx-event-id
+                    pattern: "^\\$"
                     description: A unique identifier for the event.
               examples:
                 response:
diff --git a/data/api/client-server/relations.yaml b/data/api/client-server/relations.yaml
index c4b0228c..c59c5cb0 100644
--- a/data/api/client-server/relations.yaml
+++ b/data/api/client-server/relations.yaml
@@ -233,6 +233,8 @@ components:
       example: "!636q39766251:matrix.org"
       schema:
         type: string
+        format: mx-room-id
+        pattern: "^!"
     eventId:
       in: path
       name: eventId
@@ -241,6 +243,8 @@ components:
       example: $asfDuShaf7Gafaw
       schema:
         type: string
+        format: mx-event-id
+        pattern: "^\\$"
     from:
       in: query
       name: from
diff --git a/data/api/client-server/room_event_by_timestamp.yaml b/data/api/client-server/room_event_by_timestamp.yaml
index 1ab52cb9..c47c301e 100644
--- a/data/api/client-server/room_event_by_timestamp.yaml
+++ b/data/api/client-server/room_event_by_timestamp.yaml
@@ -56,6 +56,8 @@ paths:
           example: "!636q39766251:matrix.org"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
         - in: query
           name: ts
           description: |-
@@ -86,6 +88,8 @@ paths:
                 properties:
                   event_id:
                     type: string
+                    format: mx-event-id
+                    pattern: "^\\$"
                     description: The ID of the event found
                   origin_server_ts:
                     type: integer
diff --git a/data/api/client-server/room_initial_sync.yaml b/data/api/client-server/room_initial_sync.yaml
index e9ad7a63..b9ab45ec 100644
--- a/data/api/client-server/room_initial_sync.yaml
+++ b/data/api/client-server/room_initial_sync.yaml
@@ -27,6 +27,8 @@ paths:
           example: "!636q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
       responses:
         "200":
           description: The current state of the room
@@ -38,6 +40,8 @@ paths:
                 properties:
                   room_id:
                     type: string
+                    format: mx-room-id
+                    pattern: "^!"
                     description: The ID of this room.
                   membership:
                     type: string
diff --git a/data/api/client-server/room_send.yaml b/data/api/client-server/room_send.yaml
index 7393d440..a9e35ba5 100644
--- a/data/api/client-server/room_send.yaml
+++ b/data/api/client-server/room_send.yaml
@@ -49,6 +49,8 @@ paths:
           example: "!636q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
         - in: path
           name: eventType
           description: The type of event to send.
@@ -86,6 +88,8 @@ paths:
                 properties:
                   event_id:
                     type: string
+                    format: mx-event-id
+                    pattern: "^\\$"
                     description: A unique identifier for the event.
                 required:
                   - event_id
diff --git a/data/api/client-server/room_state.yaml b/data/api/client-server/room_state.yaml
index 015f8f9d..d2b14bfe 100644
--- a/data/api/client-server/room_state.yaml
+++ b/data/api/client-server/room_state.yaml
@@ -49,6 +49,8 @@ paths:
           example: "!636q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
         - in: path
           name: eventType
           description: The type of event to send.
@@ -86,6 +88,8 @@ paths:
                 properties:
                   event_id:
                     type: string
+                    format: mx-event-id
+                    pattern: "^\\$"
                     description: A unique identifier for the event.
                 required:
                   - event_id
diff --git a/data/api/client-server/rooms.yaml b/data/api/client-server/rooms.yaml
index 3716b6a4..d4c080de 100644
--- a/data/api/client-server/rooms.yaml
+++ b/data/api/client-server/rooms.yaml
@@ -34,6 +34,8 @@ paths:
           example: "!636q39766251:matrix.org"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
         - in: path
           name: eventId
           description: The event ID to get.
@@ -41,6 +43,8 @@ paths:
           example: $asfDuShaf7Gafaw:matrix.org
           schema:
             type: string
+            format: mx-event-id
+            pattern: "^\\$"
       responses:
         "200":
           description: The full event.
@@ -89,6 +93,8 @@ paths:
           example: "!636q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
         - in: path
           name: eventType
           description: The type of state to look up.
@@ -158,6 +164,8 @@ paths:
           example: "!636q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
       responses:
         "200":
           description: The current state of the room
@@ -211,6 +219,8 @@ paths:
           example: "!636q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
         - in: query
           name: at
           description: |-
@@ -305,6 +315,8 @@ paths:
           example: "!636q39766251:example.com"
           schema:
             type: string
+            format: mx-room-id
+            pattern: "^!"
       security:
         - accessTokenQuery: []
         - accessTokenBearer: []
diff --git a/data/api/client-server/sync.yaml b/data/api/client-server/sync.yaml
index 8186dde5..c7791940 100644
--- a/data/api/client-server/sync.yaml
+++ b/data/api/client-server/sync.yaml
@@ -209,6 +209,8 @@ paths:
                                       field may be omitted.
                                     items:
                                       type: string
+                                      format: mx-user-id
+                                      pattern: "^@"
                                   m.joined_member_count:
                                     type: integer
                                     description: |-
diff --git a/data/event-schemas/schema/components/signed_third_party_invite.yaml b/data/event-schemas/schema/components/signed_third_party_invite.yaml
index b231c978..9e9ba81e 100644
--- a/data/event-schemas/schema/components/signed_third_party_invite.yaml
+++ b/data/event-schemas/schema/components/signed_third_party_invite.yaml
@@ -20,10 +20,13 @@ properties:
       The signatures are calculated using the process described at
       [Signing JSON](/appendices/#signing-json).
     type: object
-    additionalProperties:
-      type: object
-      additionalProperties:
-        type: string
+    patternProperties:
+      "":
+        x-pattern-format: mx-server-name
+        type: object
+        additionalProperties:
+          type: string
+          format: mx-unpadded-base64
     example: {
       "magic.forest": {
         "ed25519:3": "fQpGIW1Snz+pwLZu6sTy2aHy/DYWWTspTJRPyNp0PKkymfIsNffysMl6ObMMFdIJhk6g6pwlIqZ54rxo8SLmAg"
diff --git a/data/event-schemas/schema/core-event-schema/room_event.yaml b/data/event-schemas/schema/core-event-schema/room_event.yaml
index 2df24e61..921c577f 100644
--- a/data/event-schemas/schema/core-event-schema/room_event.yaml
+++ b/data/event-schemas/schema/core-event-schema/room_event.yaml
@@ -11,5 +11,7 @@ allOf:
         The ID of the room associated with this event. Will not be present on events
         that arrive through `/sync`, despite being required everywhere else.
       type: string
+      format: mx-room-id
+      pattern: "^!"
   required:
   - room_id
diff --git a/data/event-schemas/schema/core-event-schema/stripped_state.yaml b/data/event-schemas/schema/core-event-schema/stripped_state.yaml
index 6493d35b..e27ba9f1 100644
--- a/data/event-schemas/schema/core-event-schema/stripped_state.yaml
+++ b/data/event-schemas/schema/core-event-schema/stripped_state.yaml
@@ -39,6 +39,8 @@ properties:
   sender:
     description: The `sender` for the event.
     type: string
+    format: mx-user-id
+    pattern: "^@"
 required:
   - type
   - state_key
diff --git a/data/event-schemas/schema/core-event-schema/sync_room_event.yaml b/data/event-schemas/schema/core-event-schema/sync_room_event.yaml
index 2e3c0f65..bf36d18f 100644
--- a/data/event-schemas/schema/core-event-schema/sync_room_event.yaml
+++ b/data/event-schemas/schema/core-event-schema/sync_room_event.yaml
@@ -29,9 +29,13 @@ allOf:
     event_id:
       description: The globally unique event identifier.
       type: string
+      format: mx-event-id
+      pattern: "^\\$"
     sender:
       description: Contains the fully-qualified ID of the user who sent this event.
       type: string
+      format: mx-user-id
+      pattern: "^@"
     origin_server_ts:
       description: Timestamp in milliseconds on originating homeserver
         when this event was sent.
diff --git a/data/event-schemas/schema/m.room.canonical_alias.yaml b/data/event-schemas/schema/m.room.canonical_alias.yaml
index f505693a..ef67179c 100644
--- a/data/event-schemas/schema/m.room.canonical_alias.yaml
+++ b/data/event-schemas/schema/m.room.canonical_alias.yaml
@@ -16,6 +16,8 @@ properties:
           The canonical alias for the room. If not present, null, or empty the
           room should be considered to have no canonical alias.
         type: string
+        format: mx-room-alias
+        pattern: "^#"
       alt_aliases:
         description: |
           Alternative aliases the room advertises. This list can have aliases
@@ -23,6 +25,8 @@ properties:
         type: array
         items:
           type: string
+          format: mx-room-alias
+          pattern: "^#"
     type: object
   state_key:
     description: A zero-length string.
diff --git a/data/event-schemas/schema/m.room.create.yaml b/data/event-schemas/schema/m.room.create.yaml
index ed25d6d0..da8ca68e 100644
--- a/data/event-schemas/schema/m.room.create.yaml
+++ b/data/event-schemas/schema/m.room.create.yaml
@@ -12,6 +12,8 @@ properties:
           The `user_id` of the room creator. **Required** for, and only present in, room versions 1 - 10. Starting with
           room version 11 the event `sender` should be used instead.
         type: string
+        format: mx-user-id
+        pattern: "^@"
       m.federate:
         description: Whether users on other servers can join this room. Defaults to `true` if key does not exist.
         type: boolean
@@ -32,9 +34,13 @@ properties:
         properties:
           room_id:
             type: string
+            format: mx-room-id
+            pattern: "^!"
             description: The ID of the old room.
           event_id:
             type: string
+            format: mx-event-id
+            pattern: "^\\$"
             deprecated: true
             x-changedInMatrixVersion:
               "1.16": |-
@@ -51,6 +57,8 @@ properties:
         type: array
         items:
           type: string
+          format: mx-user-id
+          pattern: "^@"
           description: Additional user ID to consider a creator of the room, if supported by the room version.
         x-addedInMatrixVersion: "1.16"
         description: |-
diff --git a/data/event-schemas/schema/m.room.join_rules.yaml b/data/event-schemas/schema/m.room.join_rules.yaml
index 1bec90fc..b87e5b28 100644
--- a/data/event-schemas/schema/m.room.join_rules.yaml
+++ b/data/event-schemas/schema/m.room.join_rules.yaml
@@ -55,6 +55,8 @@ properties:
               enum: ['m.room_membership']
             room_id:
               type: string
+              format: mx-room-id
+              pattern: "^!"
               description: |-
                 Required if `type` is `m.room_membership`. The room ID to check the
                 user's membership against. If the user is joined to this room, they
diff --git a/data/event-schemas/schema/m.room.member.yaml b/data/event-schemas/schema/m.room.member.yaml
index 75510d51..aa52fae0 100644
--- a/data/event-schemas/schema/m.room.member.yaml
+++ b/data/event-schemas/schema/m.room.member.yaml
@@ -76,6 +76,8 @@ properties:
       join_authorised_via_users_server:
         x-addedInMatrixVersion: "1.2"
         type: string
+        format: mx-user-id
+        pattern: "^@"
         description: |-
           Usually found on `join` events, this field is used to denote which homeserver (through
           representation of a user with sufficient power level) authorised the user's join. More
@@ -127,6 +129,8 @@ properties:
       `join`, the user ID sending the event does not need to match the user ID in the `state_key`,
       unlike other events. Regular authorisation rules still apply.
     type: string
+    format: mx-user-id
+    pattern: "^@"
   type:
     enum:
       - m.room.member
diff --git a/data/event-schemas/schema/m.room.redaction.yaml b/data/event-schemas/schema/m.room.redaction.yaml
index 06ad8602..de6150eb 100644
--- a/data/event-schemas/schema/m.room.redaction.yaml
+++ b/data/event-schemas/schema/m.room.redaction.yaml
@@ -10,6 +10,8 @@ properties:
       redacts:
         description: The event ID that was redacted. Required for, and present starting in, room version 11.
         type: string
+        format: mx-event-id
+        pattern: "^\\$"
       reason:
         description: 'The reason for the redaction, if any.'
         type: string
@@ -17,6 +19,8 @@ properties:
   redacts:
     description: Required for, and only present in, room versions 1 - 10. The event ID that was redacted.
     type: string
+    format: mx-event-id
+    pattern: "^\\$"
   type:
     enum:
       - m.room.redaction
diff --git a/data/string-formats.yaml b/data/string-formats.yaml
index fca325b9..9d41c402 100644
--- a/data/string-formats.yaml
+++ b/data/string-formats.yaml
@@ -66,6 +66,11 @@ mx-mxc-uri:
   url: client-server-api#matrix-content-mxc-uris
   # regex: "^mxc:\\/\\/"
 
+mx-unpadded-base64:
+  title: Unpadded Base64
+  url: appendices#unpadded-base64
+  # no regex
+
 uri:
   title: URI
   url: https://datatracker.ietf.org/doc/html/rfc3986