diff --git a/src/networkRequest.ts b/src/networkRequest.ts
index 95fead0..3b4695c 100644
--- a/src/networkRequest.ts
+++ b/src/networkRequest.ts
@@ -6,5 +6,19 @@ export const networkRequest = async (
   url: string,
 ): Promise<Record<string, unknown>> => {
   const result = await fetch(url);
+
+  const { status, headers } = result;
+
+  if (status < 200 || status >= 300) {
+    const body = await result.text();
+    throw new Error(`HTTP request failed (${status}): ${body}`);
+  }
+
+  const contentType = headers.get('content-type');
+  if (contentType?.includes('application/json') === false) {
+    const body = await result.text();
+    throw new Error(`HTTP response is not JSON but ${contentType}: ${body}`);
+  }
+
   return result.json();
 };