diff --git a/changelogs/client_server/newsfragments/1978.clarification b/changelogs/client_server/newsfragments/1978.clarification
new file mode 100644
index 00000000..bdcce777
--- /dev/null
+++ b/changelogs/client_server/newsfragments/1978.clarification
@@ -0,0 +1 @@
+Clarify formats of string types.
diff --git a/data/api/client-server/support.yaml b/data/api/client-server/support.yaml
index 1598d5d7..b9ca062e 100644
--- a/data/api/client-server/support.yaml
+++ b/data/api/client-server/support.yaml
@@ -54,6 +54,8 @@ paths:
                       properties:
                         matrix_id:
                           type: string
+                          format: mx-user-id
+                          pattern: "^@"
                           description: |-
                             A [Matrix User ID](/appendices/#user-identifiers)
                             representing the administrator.
@@ -66,6 +68,7 @@ paths:
                             required.
                         email_address:
                           type: string
+                          format: email
                           description: |-
                             An email address to reach the administrator.
 
@@ -95,6 +98,7 @@ paths:
                       }
                   support_page:
                     type: string
+                    format: uri
                     description: |-
                       The URL of a page to give users help specific to the
                       homeserver, like extra login/registration steps.
diff --git a/data/string-formats.yaml b/data/string-formats.yaml
index e4ebc523..4ffe219c 100644
--- a/data/string-formats.yaml
+++ b/data/string-formats.yaml
@@ -64,3 +64,7 @@ mx-mxc-uri:
 uri:
   title: URI
   url: https://datatracker.ietf.org/doc/html/rfc3986
+
+email:
+  title: Email Address
+  url: https://datatracker.ietf.org/doc/html/rfc5321#section-4.1.2