When you use the Shopify recommended upsell type, Cartly doesn't guess what to recommend — it asks Shopify. Shopify has two different ways of deciding which products go together, and Cartly now lets you choose which one to use.
Table of contents:
The two recommendation algorithms
Both algorithms are cart-aware: they look at what's already in the shopper's cart and recommend products based on it. The difference is who decides which products go together.
Related — Shopify decides automatically
Shopify picks the products for you using its own recommendation logic: real order history, product descriptions, related collections, and product types in your store.
No configuration needed — it works the moment you enable it
Recommendations improve on their own as your store collects more orders
You don't control which products appear
This is the behavior Cartly used before the algorithm selector was introduced, so if you don't change anything, nothing changes for your store.
💡 Want upsells without any manual work? Choose Related. It's the only one of the two that Shopify generates automatically — no product pairing, no maintenance, nothing to keep up to date as your catalogue grows.
Complementary — you decide manually
You tell Shopify which products go with which, product by product, in Shopify's free Search & Discovery app. Cartly then shows exactly the products you paired.
Full control over every recommendation
Ideal for genuine accessories and add-ons — a case for a phone, a filter for a jug, batteries for a toy
Requires manual setup for each product you want upsells for. Shopify does not generate complementary pairings automatically — this is documented on Shopify's side, and it's the main trade-off to weigh against Related.
How to choose an algorithm in Cartly
In your Cartly dashboard, go to Custom Cart → Upsell → Upsells and cross-sells and make sure the feature is enabled.
Tick Shopify recommended as the upsell type.
Choose the recommendation algorithm: Related or Complementary.
If you chose Complementary, use the link to open Search & Discovery and pair your products there (see the next section).
Check the preview and click Save.
How to set up complementary products in Search & Discovery
Complementary recommendations live in Shopify, not in Cartly — Cartly reads whatever you configure there. Search & Discovery is a free app built by Shopify and is already installed on most stores. If yours doesn't have it, you can install it from the Shopify App Store: Shopify Search & Discovery.
Step 1. Open the Search & Discovery app in your Shopify admin, or use the link in Cartly's upsell settings.
Step 2. Go to Product recommendations. You'll see a list of your products — select the one you want to configure upsells for.
Step 3. Under Complementary products, click Browse and select the products you want to recommend alongside it. Save your changes.
Step 4. Repeat for every product you want to drive upsells.
Example: you add Yoga Mat Strap and Cork Yoga Block as complementary products for Yoga Mat. From then on, whenever a shopper has the Yoga Mat in their cart, Cartly's upsell block shows the strap and the block.
Changes you make in Search & Discovery apply to your storefront — you don't need to re-save anything in Cartly for them to take effect.
Which algorithm should I use?
Pick Related if you have a large catalogue, a steady order history, or simply want upsells running without ongoing maintenance.
Pick Complementary if your products have clear, obvious partners, or if you want to push specific high-margin add-ons — and you're willing to pair them yourself.
New store with few orders? Complementary usually performs better at first, because Shopify's automatic recommendations need order data to become accurate.
Good to know
Complementary shows nothing for unconfigured products. If a product in the cart has no complementary products set in Search & Discovery, there's nothing for Cartly to show for it. If your upsell block looks empty, that's the first thing to check.
The block always follows the cart. If the shopper removes a product, the recommendations update to match whatever is still in the cart.
Up to 10 products can be displayed in a Shopify recommended upsell block.
Products already in the cart, out-of-stock products, gift cards, and products priced at 0 are never recommended — that's Shopify's own rule and applies to both algorithms.
You can combine this with manual rules. When both upsell types are enabled, your manual rules are applied first and Shopify recommendations fill the remaining slots. See Creating upsell cart drawers.
Need Help?
If you have any questions, please contact our support team.
📩 Contact Support: Reach out to us via live chat or send an email to [email protected]