diff --git a/web/src/api/queries.fields.test.tsx b/web/src/api/queries.fields.test.tsx
new file mode 100644
index 0000000..6ed0f4c
--- /dev/null
+++ b/web/src/api/queries.fields.test.tsx
@@ -0,0 +1,40 @@
+import { expect, test } from "vitest";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { renderHook, waitFor } from "@testing-library/react";
+import { http, HttpResponse } from "msw";
+import { server } from "../test/server";
+import { useCreateFieldDefinition } from "./queries";
+
+function wrapper({ children }: { children: React.ReactNode }) {
+  const qc = new QueryClient({ defaultOptions: { queries: { retry: false }, mutations: { retry: false } } });
+
+  return <QueryClientProvider client={qc}>{children}</QueryClientProvider>;
+}
+
+test("useCreateFieldDefinition POSTs the request body", async () => {
+  let body: unknown;
+
+  server.use(
+    http.post("/api/admin/field-definitions", async ({ request }) => {
+      body = await request.json();
+
+      return HttpResponse.json({ key: "technique" }, { status: 201 });
+    }),
+  );
+
+  const { result } = renderHook(() => useCreateFieldDefinition(), { wrapper });
+
+  result.current.mutate({
+    key: "technique",
+    data_type: "term",
+    vocabulary_id: "v-technique",
+    authority_kind: null,
+    required: false,
+    group: "Provenance",
+    labels: [{ lang: "en", label: "Technique" }],
+  });
+
+  await waitFor(() => expect(result.current.isSuccess).toBe(true));
+  expect((body as { key: string }).key).toBe("technique");
+  expect((body as { data_type: string }).data_type).toBe("term");
+});
diff --git a/web/src/api/queries.ts b/web/src/api/queries.ts
index 668f6f2..0825ec9 100644
--- a/web/src/api/queries.ts
+++ b/web/src/api/queries.ts
@@ -315,6 +315,23 @@ export function useSearch(q: string, visibility: string | null) {
   });
 }
 
+type NewFieldDefinitionRequest = components["schemas"]["NewFieldDefinitionRequest"];
+
+export function useCreateFieldDefinition() {
+  const qc = useQueryClient();
+
+  return useMutation({
+    mutationFn: async (body: NewFieldDefinitionRequest) => {
+      const { data, response } = await api.POST("/api/admin/field-definitions", { body });
+
+      if (response.status !== 201 || !data) throw new Error("failed to create field definition");
+
+      return data;
+    },
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["field-definitions"] }),
+  });
+}
+
 type Visibility = "draft" | "internal" | "public";
 
 /** Error carrying the HTTP status so callers can branch 422-gate vs 409-illegal. */
diff --git a/web/src/test/handlers.ts b/web/src/test/handlers.ts
index 81d0d89..f6dcfba 100644
--- a/web/src/test/handlers.ts
+++ b/web/src/test/handlers.ts
@@ -68,4 +68,8 @@ export const handlers = [
   http.post("/api/admin/logout", () => new HttpResponse(null, { status: 204 })),
 
   http.post("/api/admin/objects/:id/visibility", () => new HttpResponse(null, { status: 204 })),
+
+  http.post("/api/admin/field-definitions", () =>
+    HttpResponse.json({ key: "new_field" }, { status: 201 }),
+  ),
 ];