diff --git a/src/lib/shopifyCollections.ts b/src/lib/shopifyCollections.ts
new file mode 100644
index 0000000..5133df6
--- /dev/null
+++ b/src/lib/shopifyCollections.ts
@@ -0,0 +1,27 @@
+const API_VERSION = '2024-01'
+
+function getConfig() {
+  const domain = process.env.SHOPIFY_STORE_DOMAIN
+  const token = process.env.SHOPIFY_ADMIN_API_TOKEN
+  if (!domain || !token) throw new Error('SHOPIFY_STORE_DOMAIN et SHOPIFY_ADMIN_API_TOKEN requis')
+  return {
+    baseUrl: `https://${domain}/admin/api/${API_VERSION}`,
+    headers: { 'X-Shopify-Access-Token': token, 'Content-Type': 'application/json' },
+  }
+}
+
+export async function addProductToCollection(shopifyProductId: string, collectionId: string): Promise<void> {
+  if (!collectionId?.trim()) return
+  const { baseUrl, headers } = getConfig()
+  const res = await fetch(`${baseUrl}/collects.json`, {
+    method: 'POST',
+    headers,
+    body: JSON.stringify({ collect: { product_id: shopifyProductId, collection_id: collectionId } }),
+  })
+  if (!res.ok) {
+    const err = await res.text()
+    if (!err.includes('already') && !err.includes('taken')) {
+      throw new Error(`Shopify addToCollection error: ${res.status} — ${err}`)
+    }
+  }
+}