diff --git a/example-retrieval-plugin/plugin/src/index.js b/example-retrieval-plugin/plugin/src/index.js
index eba75dc..736cdb6 100644
--- a/example-retrieval-plugin/plugin/src/index.js
+++ b/example-retrieval-plugin/plugin/src/index.js
@@ -65,6 +65,10 @@ async function retrievalPluginQuery(request, env, ctx) {
   /** @type {QueryRequest} */
   const { queries } = await request.json();
 
+  if (queries == null || !Array.isArray(queries)) {
+    throw new Error("unexpected json payload");
+  }
+
   let topKs = await Promise.all(
     queries.map(({ query, top_k: topK }) => queryVectorStore(env, query, topK))
   );
@@ -101,9 +105,17 @@ const CHUNK_TTL = 24 * 60 * 60; // 24 hours
  * @returns {Promise<(Chunk & {similarity: number})[]>}
  */
 async function queryVectorStore(env, query, topK = 3) {
+  if (!query) {
+    throw new Error("query is empty");
+  }
+  if (!env.OPENAI_API_KEY) {
+    throw new Error("OPENAI_API_KEY is not set");
+  }
   const res = await fetchEmbeddings([query], env.OPENAI_API_KEY);
   if (res.error != null) {
-    throw new Error(res.error);
+    const err = new Error(res.error.message || String(res.error));
+    err.cause = res.error;
+    throw err;
   }
   const queryEmbedding = res.data[0].embedding;
 
diff --git a/example-retrieval-plugin/scheduler/src/index.js b/example-retrieval-plugin/scheduler/src/index.js
index 6b3eacc..f1a0f70 100644
--- a/example-retrieval-plugin/scheduler/src/index.js
+++ b/example-retrieval-plugin/scheduler/src/index.js
@@ -14,6 +14,12 @@ const EMBEDDINGS_KEY = "embeddings:v1";
 /** @type {ExportedHandler<Env, EmbeddingMessage>} */
 export default {
   async scheduled(controller, env, ctx) {
+    if (!env.GITHUB_API_KEY) {
+      throw new Error("GITHUB_API_KEY is not set");
+    }
+    if (!env.OPENAI_API_KEY) {
+      throw new Error("OPENAI_API_KEY is not set");
+    }
     ctx.waitUntil(scheduleEmbeddings(env, ctx));
     console.log("scheduled ok");
   },
diff --git a/example-retrieval-plugin/shared/openai.js b/example-retrieval-plugin/shared/openai.js
index 3846a24..eecd9f8 100644
--- a/example-retrieval-plugin/shared/openai.js
+++ b/example-retrieval-plugin/shared/openai.js
@@ -3,7 +3,7 @@ const OPENAI_BASE = "https://api.openai.com/v1";
 /**
  * @param {string[]} chunks
  * @param {string} apiKey
- * @returns {Promise<{data: {embedding: number[]}[], error?: string}>}
+ * @returns {Promise<{data: {embedding: number[]}[], error?: {message: string, type: string}}>}
  */
 export async function fetchEmbeddings(chunks, apiKey) {
   const NUM_RETRIES = 100;