diff --git a/apps/api/src/admin.ts b/apps/api/src/admin.ts
index 73de3c5..450496c 100644
--- a/apps/api/src/admin.ts
+++ b/apps/api/src/admin.ts
@@ -29,7 +29,7 @@ export function renderLogin(message = "") {
   );
 }
 
-export function renderAdmin(cards: BoardCard[], options: { storageMode: string }) {
+export function renderAdmin(cards: BoardCard[], options: { storageMode: string; message?: string }) {
   const sorted = [...cards].sort((a, b) => Date.parse(b.updatedAt) - Date.parse(a.updatedAt));
 
   return pageShell(
@@ -52,6 +52,12 @@ export function renderAdmin(cards: BoardCard[], options: { storageMode: string }
           </aside>
         </header>
 
+        ${
+          options.message
+            ? `<section class="noticeBanner">${escapeHtml(options.message)}</section>`
+            : ""
+        }
+
         <section class="workbench">
           <form class="editor" method="post" action="/admin/cards" enctype="multipart/form-data">
             <p class="stamp">New card</p>
@@ -201,7 +207,8 @@ textarea {
 .mast,
 .editor,
 .cardEditor,
-.empty {
+.empty,
+.noticeBanner {
   border: 2px solid var(--color-line);
   background: var(--color-panel);
   box-shadow: var(--shadow-hard);
@@ -283,10 +290,18 @@ h1 {
 
 .editor,
 .cardEditor,
-.empty {
+.empty,
+.noticeBanner {
   padding: 18px;
 }
 
+.noticeBanner {
+  margin-top: 28px;
+  color: var(--color-ink);
+  font-family: var(--font-mono);
+  overflow-wrap: anywhere;
+}
+
 .editor {
   position: sticky;
   top: 18px;
diff --git a/apps/api/src/index.ts b/apps/api/src/index.ts
index 12308f9..c051e44 100644
--- a/apps/api/src/index.ts
+++ b/apps/api/src/index.ts
@@ -104,6 +104,10 @@ async function cardFromForm(form: FormData, existing?: BoardCard): Promise<Board
   };
 }
 
+async function renderAdminWithMessage(message: string, status = 500) {
+  return html(renderAdmin(await readCards(), { storageMode, message }), { status });
+}
+
 const app = new Elysia()
   .use(
     swagger({
@@ -246,17 +250,21 @@ const app = new Elysia()
       return redirect("/admin");
     }
 
-    const form = await request.formData();
-    const cards = await readCards();
-    const id = String(form.get("id") || "");
-    const existing = cards.find((card) => card.id === id);
-    const nextCard = await cardFromForm(form, existing);
-    const nextCards = existing
-      ? cards.map((card) => (card.id === existing.id ? nextCard : card))
-      : [nextCard, ...cards];
+    try {
+      const form = await request.formData();
+      const cards = await readCards();
+      const id = String(form.get("id") || "");
+      const existing = cards.find((card) => card.id === id);
+      const nextCard = await cardFromForm(form, existing);
+      const nextCards = existing
+        ? cards.map((card) => (card.id === existing.id ? nextCard : card))
+        : [nextCard, ...cards];
 
-    await writeCards(nextCards);
-    return redirect("/admin");
+      await writeCards(nextCards);
+      return redirect("/admin");
+    } catch (error) {
+      return renderAdminWithMessage(error instanceof Error ? error.message : "Could not save card.");
+    }
   }, {
     detail: {
       tags: ["admin"],
@@ -269,17 +277,21 @@ const app = new Elysia()
       return redirect("/admin");
     }
 
-    const form = await request.formData();
-    const id = String(form.get("id") || "");
-    const cards = await readCards();
-    const existing = cards.find((card) => card.id === id);
+    try {
+      const form = await request.formData();
+      const id = String(form.get("id") || "");
+      const cards = await readCards();
+      const existing = cards.find((card) => card.id === id);
 
-    if (existing?.imageUrl) {
-      await deleteRemoteImage(existing.imageUrl);
+      if (existing?.imageUrl) {
+        await deleteRemoteImage(existing.imageUrl);
+      }
+
+      await writeCards(cards.filter((card) => card.id !== id));
+      return redirect("/admin");
+    } catch (error) {
+      return renderAdminWithMessage(error instanceof Error ? error.message : "Could not delete card.");
     }
-
-    await writeCards(cards.filter((card) => card.id !== id));
-    return redirect("/admin");
   }, {
     detail: {
       tags: ["admin"],
diff --git a/apps/api/src/store.ts b/apps/api/src/store.ts
index d69f9b1..8ac31e4 100644
--- a/apps/api/src/store.ts
+++ b/apps/api/src/store.ts
@@ -17,10 +17,13 @@ const localDataDir = path.resolve(".data");
 const localUploadsDir = path.join(localDataDir, "uploads");
 const localCardsPath = path.join(localDataDir, "cards.json");
 
-export const storageMode = process.env.BLOB_READ_WRITE_TOKEN ? "Vercel Blob" : "Local file";
+const hasBlobToken = () => Boolean(process.env.BLOB_READ_WRITE_TOKEN?.trim());
+const isVercel = () => process.env.VERCEL === "1";
+
+export const storageMode = hasBlobToken() ? "Vercel Blob" : "Local file";
 
 export async function readCards(): Promise<BoardCard[]> {
-  if (process.env.BLOB_READ_WRITE_TOKEN) {
+  if (hasBlobToken()) {
     try {
       const result = await get(dataBlobPath, { access: "private" });
       if (!result?.stream) {
@@ -47,7 +50,7 @@ export async function readCards(): Promise<BoardCard[]> {
 export async function writeCards(cards: BoardCard[]) {
   const content = JSON.stringify(cards, null, 2);
 
-  if (process.env.BLOB_READ_WRITE_TOKEN) {
+  if (hasBlobToken()) {
     await put(dataBlobPath, content, {
       access: "private",
       contentType: "application/json",
@@ -56,6 +59,7 @@ export async function writeCards(cards: BoardCard[]) {
     return;
   }
 
+  assertWritableLocalStorage();
   await mkdir(localDataDir, { recursive: true });
   await writeFile(localCardsPath, content, "utf8");
 }
@@ -64,7 +68,7 @@ export async function saveImage(file: File) {
   const safeName = safeFileName(file.name || "image");
   const pathname = `pozor/images/${Date.now()}-${safeName}`;
 
-  if (process.env.BLOB_READ_WRITE_TOKEN) {
+  if (hasBlobToken()) {
     const blob = await put(pathname, file, {
       access: "public",
       contentType: file.type || "application/octet-stream"
@@ -72,6 +76,7 @@ export async function saveImage(file: File) {
     return blob.url;
   }
 
+  assertWritableLocalStorage();
   await mkdir(localUploadsDir, { recursive: true });
   const localName = `${Date.now()}-${safeName}`;
   const localPath = path.join(localUploadsDir, localName);
@@ -80,7 +85,7 @@ export async function saveImage(file: File) {
 }
 
 export async function deleteRemoteImage(imageUrl: string) {
-  if (!process.env.BLOB_READ_WRITE_TOKEN || !imageUrl.includes(".blob.vercel-storage.com/")) {
+  if (!hasBlobToken() || !imageUrl.includes(".blob.vercel-storage.com/")) {
     return;
   }
 
@@ -95,6 +100,16 @@ export function localUploadPath(filename: string) {
   return path.join(localUploadsDir, safeFileName(filename));
 }
 
+function assertWritableLocalStorage() {
+  if (!isVercel()) {
+    return;
+  }
+
+  throw new Error(
+    "BLOB_READ_WRITE_TOKEN is not set for the API deployment. Vercel functions cannot write to .data; connect Vercel Blob to the API project and redeploy."
+  );
+}
+
 export function publicCards(cards: BoardCard[]) {
   return cards
     .filter((card) => card.published)