diff --git a/crates/api/src/admin.rs b/crates/api/src/admin.rs
index 07587c7..bf02cbe 100644
--- a/crates/api/src/admin.rs
+++ b/crates/api/src/admin.rs
@@ -32,7 +32,6 @@ pub(crate) struct UserView {
 /// Desired visibility for a publish/unpublish request.
 #[derive(Deserialize, ToSchema)]
 pub(crate) struct VisibilityRequest {
-    #[schema(value_type = String)]
     pub visibility: Visibility,
 }
 
diff --git a/crates/api/src/admin_authorities.rs b/crates/api/src/admin_authorities.rs
index 87d3fba..58fc79d 100644
--- a/crates/api/src/admin_authorities.rs
+++ b/crates/api/src/admin_authorities.rs
@@ -20,6 +20,7 @@ use crate::{
 #[derive(Serialize, ToSchema)]
 pub(crate) struct AuthorityView {
     pub id: String,
+    #[schema(value_type = domain::AuthorityKind)]
     pub kind: String,
     pub external_uri: Option<String>,
     pub labels: Vec<LabelView>,
diff --git a/crates/api/src/admin_objects.rs b/crates/api/src/admin_objects.rs
index 1b2d1b6..72ea003 100644
--- a/crates/api/src/admin_objects.rs
+++ b/crates/api/src/admin_objects.rs
@@ -40,9 +40,10 @@ pub(crate) struct AdminObjectView {
     /// `YYYY-MM-DD` or null.
     pub recording_date: Option<String>,
     /// "draft" | "internal" | "public".
+    #[schema(value_type = domain::Visibility)]
     pub visibility: String,
     /// Flexible field values (key -> value).
-    #[schema(value_type = Object)]
+    #[schema(value_type = std::collections::HashMap<String, serde_json::Value>)]
     pub fields: serde_json::Value,
 }
 
@@ -162,7 +163,6 @@ pub(crate) struct ObjectCreateRequest {
     pub recorder: Option<String>,
     pub recording_date: Option<String>,
     /// "draft" | "internal" (public is rejected — publish via the visibility endpoint).
-    #[schema(value_type = String)]
     pub visibility: Visibility,
 }
 
@@ -360,8 +360,10 @@ pub(crate) async fn delete_object(
 pub(crate) struct FieldDefinitionView {
     pub key: String,
     /// "text" | "localized_text" | "integer" | "date" | "boolean" | "term" | "authority".
+    #[schema(value_type = domain::DataType)]
     pub data_type: String,
     pub vocabulary_id: Option<String>,
+    #[schema(value_type = Option<domain::AuthorityKind>)]
     pub authority_kind: Option<String>,
     pub required: bool,
     pub group: Option<String>,
diff --git a/crates/api/src/openapi.rs b/crates/api/src/openapi.rs
index e40d9ba..ea75cbc 100644
--- a/crates/api/src/openapi.rs
+++ b/crates/api/src/openapi.rs
@@ -59,7 +59,10 @@ use crate::{
         admin_search::SearchHitView,
         admin_search::SearchResultsView,
         admin_authorities::AuthorityView,
-        admin_authorities::NewAuthorityRequest
+        admin_authorities::NewAuthorityRequest,
+        domain::Visibility,
+        domain::AuthorityKind,
+        domain::DataType
     )),
     info(title = "Collection Management System", version = "0.0.0")
 )]
diff --git a/web/src/api/schema.d.ts b/web/src/api/schema.d.ts
index e372e04..e0095dc 100644
--- a/web/src/api/schema.d.ts
+++ b/web/src/api/schema.d.ts
@@ -326,7 +326,9 @@ export interface components {
             current_location?: string | null;
             current_owner?: string | null;
             /** @description Flexible field values (key -> value). */
-            fields: Record<string, never>;
+            fields: {
+                [key: string]: unknown;
+            };
             id: string;
             /** Format: int32 */
             number_of_objects: number;
@@ -336,12 +338,21 @@ export interface components {
             /** @description `YYYY-MM-DD` or null. */
             recording_date?: string | null;
             /** @description "draft" | "internal" | "public". */
-            visibility: string;
+            visibility: components["schemas"]["Visibility"];
         };
+        /**
+         * @description The kind of authority record.
+         *
+         *     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.
+         * @enum {string}
+         */
+        AuthorityKind: "person" | "organisation" | "place";
         AuthorityView: {
             external_uri?: string | null;
             id: string;
-            kind: string;
+            kind: components["schemas"]["AuthorityKind"];
             labels: components["schemas"]["LabelView"][];
         };
         CreatedField: {
@@ -354,11 +365,18 @@ export interface components {
         CreatedObject: {
             id: string;
         };
+        /**
+         * @description 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`.
+         * @enum {string}
+         */
+        DataType: "text" | "localized_text" | "integer" | "date" | "boolean" | "term" | "authority";
         /** @description Field-definition descriptor for the UI to render forms. */
         FieldDefinitionView: {
-            authority_kind?: string | null;
+            authority_kind?: null | components["schemas"]["AuthorityKind"];
             /** @description "text" | "localized_text" | "integer" | "date" | "boolean" | "term" | "authority". */
-            data_type: string;
+            data_type: components["schemas"]["DataType"];
             group?: string | null;
             key: string;
             labels: components["schemas"]["LabelView"][];
@@ -419,7 +437,7 @@ export interface components {
             recorder?: string | null;
             recording_date?: string | null;
             /** @description "draft" | "internal" (public is rejected — publish via the visibility endpoint). */
-            visibility: string;
+            visibility: components["schemas"]["Visibility"];
         };
         /**
          * @description Inventory-minimum fields for update. Visibility is intentionally absent — it changes
@@ -488,9 +506,14 @@ export interface components {
             id: string;
             role: string;
         };
+        /**
+         * @description Publication state of a catalogue record.
+         * @enum {string}
+         */
+        Visibility: "draft" | "internal" | "public";
         /** @description Desired visibility for a publish/unpublish request. */
         VisibilityRequest: {
-            visibility: string;
+            visibility: components["schemas"]["Visibility"];
         };
         VocabularyView: {
             id: string;