diff --git a/agent.md b/agent.md
index 4a25f26..f022f3c 100644
--- a/agent.md
+++ b/agent.md
@@ -132,7 +132,7 @@ On mobile (< 620 px): scan input goes full-width on its own row; user dropdown a
 
 ## Key behaviours
 - **On load**: cookie credentials restored → GET webhook fires → dropdown populated → scan input auto-focused
-- **Enter key**: trims input, POSTs to webhook, prepends result row, clears + re-focuses input
+- **Enter key**: trims input → **duplicate check** → POSTs to webhook, prepends result row, clears + re-focuses input
 - **Clear button**: empties the table, clears the scan input, resets the scan counter
 - **No user selected**: red toast + highlighted dropdown; does not submit
 - **401 on any request**: modal prompts for credentials (pre-filled from cookie), saves to cookie, retries original call
@@ -140,6 +140,15 @@ On mobile (< 620 px): scan input goes full-width on its own row; user dropdown a
 - **Network error**: dismissing error banner; input selected so user can retry
 - **Dropdown error state**: tapping/focusing the dropdown while it shows an error re-triggers `loadUsers()`
 - **NDJSON/array/object**: `parseJson()` normalises all response formats from n8n
+- **Duplicate scan**: `isDuplicate(code)` queries `.col-code` cells in the live table before every POST; if found, shows a warning toast and skips the webhook call entirely
+
+## Table columns (DOM)
+| Visible | Header | CSS class | Content |
+|---------|--------|-----------|---------|
+| ✓ | Country | — | `item.country` wrapped in teal badge |
+| ✓ | Name | `name-cell` | `item.name` |
+| ✓ | Tag | — | `item.producttag` in monospace pill |
+| ✗ | Code | `col-code` | Raw scanned code (`display:none`), used for duplicate detection |
 
 ## How to run
 Open `index.html` directly in a browser (`file://`) — no server needed for local use.
diff --git a/index.html b/index.html
index 7051c61..275adff 100644
--- a/index.html
+++ b/index.html
@@ -396,6 +396,11 @@
                 width: 200px;
             }
 
+            /* Hidden code column — stores raw scan code for duplicate checking */
+            .col-code {
+                display: none;
+            }
+
             tbody tr {
                 border-bottom: 1px solid var(--card);
                 animation: rowIn 0.28s ease-out;
@@ -881,6 +886,7 @@
                             <th>Country</th>
                             <th>Name</th>
                             <th>Tag</th>
+                            <th class="col-code">Code</th>
                         </tr>
                     </thead>
                     <tbody id="tableBody"></tbody>
@@ -1201,6 +1207,15 @@
                 });
             }
 
+            // ── Duplicate check ──────────────────────────────────────────────────────
+            function isDuplicate(code) {
+                const cells = tableBody.querySelectorAll(".col-code");
+                for (const cell of cells) {
+                    if (cell.textContent === code.trim()) return true;
+                }
+                return false;
+            }
+
             // ── Submit Scan ──────────────────────────────────────────────────────────
             async function submitScan(code) {
                 const user = userSelect.value;
@@ -1216,6 +1231,17 @@
                     return;
                 }
 
+                // Duplicate check against already-scanned codes in the table
+                if (isDuplicate(code)) {
+                    showToast(
+                        "⚠️ Already scanned: " + code.trim(),
+                        "fail",
+                        4000,
+                    );
+                    scanInput.select();
+                    return;
+                }
+
                 showBanner("Looking up package…", "loading");
 
                 try {
@@ -1253,7 +1279,7 @@
                         return;
                     }
                     hideBanner();
-                    addRow(item);
+                    addRow(item, code);
                     showToast(
                         "✓ Added: " + (item.name || item.producttag || code),
                         "ok",
@@ -1273,8 +1299,8 @@
                 }
             }
 
-            // ── Table Row ────────────────────────────────────────────────────────────
-            function addRow(item) {
+            // ── Table Row ───────────────────────────────────────────────────────────────────
+            function addRow(item, code) {
                 emptyState.style.display = "none";
                 scanCount++;
                 countPill.textContent =
@@ -1286,6 +1312,7 @@
         <td><span class="country-badge">${esc(item.country || "—")}</span></td>
         <td class="name-cell">${esc(item.name || "—")}</td>
         <td><span class="tag-pill" title="${esc(item.producttag || "")}">${esc(item.producttag || "—")}</span></td>
+        <td class="col-code">${esc(code.trim())}</td>
       `;
                 // Newest row at the top
                 tableBody.insertBefore(tr, tableBody.firstChild);