diff --git a/changelogs/client_server/newsfragments/1979.clarification b/changelogs/client_server/newsfragments/1979.clarification
new file mode 100644
index 000000000..bdcce7771
--- /dev/null
+++ b/changelogs/client_server/newsfragments/1979.clarification
@@ -0,0 +1 @@
+Clarify formats of string types.
diff --git a/data/api/client-server/definitions/m.login.terms_params.yaml b/data/api/client-server/definitions/m.login.terms_params.yaml
index 67001c189..50c9da43e 100644
--- a/data/api/client-server/definitions/m.login.terms_params.yaml
+++ b/data/api/client-server/definitions/m.login.terms_params.yaml
@@ -50,6 +50,7 @@ properties:
               arbitrary string with no specified maximum length.
           url:
             type: string
+            format: uri
             description: |
               A link to the text of this document, in the appropriate
               language. MUST be a valid URI with scheme `https://` or