diff --git a/crates/domain/Cargo.toml b/crates/domain/Cargo.toml
index d831a62..39631df 100644
--- a/crates/domain/Cargo.toml
+++ b/crates/domain/Cargo.toml
@@ -9,3 +9,4 @@ uuid.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 time.workspace = true
+utoipa.workspace = true
diff --git a/crates/domain/src/authority.rs b/crates/domain/src/authority.rs
index 7cc550e..aa375e7 100644
--- a/crates/domain/src/authority.rs
+++ b/crates/domain/src/authority.rs
@@ -7,7 +7,7 @@ use crate::{AuthorityId, LocalizedLabel};
 /// NOTE: kept in sync by hand with the
 /// `CHECK (kind IN ('person', 'organisation', 'place'))` constraint in
 /// `crates/db/migrations/0002_vocabularies_authorities.sql` — add a variant in both places.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, utoipa::ToSchema)]
 #[serde(rename_all = "lowercase")]
 pub enum AuthorityKind {
     Person,
diff --git a/crates/domain/src/field_definition.rs b/crates/domain/src/field_definition.rs
index 45d83ef..66fa47f 100644
--- a/crates/domain/src/field_definition.rs
+++ b/crates/domain/src/field_definition.rs
@@ -74,6 +74,23 @@ impl FieldType {
     }
 }
 
+/// The stored `data_type` discriminant of a field definition — mirrors the strings from
+/// [`FieldType::kind_str`]. Exists so the OpenAPI schema can describe `data_type` as a
+/// closed string enum (consumed by the typed web client). Keep in sync with `kind_str`.
+#[derive(
+    Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize, utoipa::ToSchema,
+)]
+#[serde(rename_all = "snake_case")]
+pub enum DataType {
+    Text,
+    LocalizedText,
+    Integer,
+    Date,
+    Boolean,
+    Term,
+    Authority,
+}
+
 /// A registered flexible field, with its multilingual display labels.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct FieldDefinition {
@@ -152,4 +169,18 @@ mod tests {
         );
         assert_eq!(FieldType::from_parts("authority", Some(v), None), None);
     }
+
+    #[test]
+    fn data_type_serde_matches_kind_str() {
+        use serde_json::json;
+        assert_eq!(
+            serde_json::to_value(DataType::LocalizedText).unwrap(),
+            json!("localized_text")
+        );
+        assert_eq!(serde_json::to_value(DataType::Text).unwrap(), json!("text"));
+        assert_eq!(
+            serde_json::to_value(DataType::Authority).unwrap(),
+            json!("authority")
+        );
+    }
 }
diff --git a/crates/domain/src/lib.rs b/crates/domain/src/lib.rs
index fa3f759..e10dc2c 100644
--- a/crates/domain/src/lib.rs
+++ b/crates/domain/src/lib.rs
@@ -11,7 +11,7 @@ mod vocabulary;
 
 pub use audit::{AuditAction, AuditActor, AuditEntry, FieldChange, NewAuditEvent};
 pub use authority::{Authority, AuthorityKind, AuthorityRef, NewAuthority};
-pub use field_definition::{FieldDefinition, FieldType, NewFieldDefinition};
+pub use field_definition::{DataType, FieldDefinition, FieldType, NewFieldDefinition};
 pub use id::{AuthorityId, FieldDefinitionId, ObjectId, OrgId, TermId, UserId, VocabularyId};
 pub use label::{LocalizedLabel, pick_label};
 pub use object::{CatalogueObject, IllegalTransition, ObjectInput, Visibility};
diff --git a/crates/domain/src/object.rs b/crates/domain/src/object.rs
index eb3ded6..6754ef9 100644
--- a/crates/domain/src/object.rs
+++ b/crates/domain/src/object.rs
@@ -4,7 +4,7 @@ use time::{Date, OffsetDateTime};
 use crate::ObjectId;
 
 /// Publication state of a catalogue record.
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default, utoipa::ToSchema)]
 #[serde(rename_all = "lowercase")]
 pub enum Visibility {
     /// Work in progress; not shown anywhere public.