A note before you read: we make Posto, so we're not neutral. We've tried to be fair anyway. Everything about Sidekick below comes from Shopify's own help center and blog, checked on October 2, 2026, and we say plainly where Sidekick is all you need.
The short version
Sidekick is free, already in your Shopify admin, and good at answering a question when you ask it. If you have a few products, buy from one or two suppliers, and remember to check in, it may be enough. Posto is for stores where reordering is a routine: many products, several suppliers with their own rules, and orders that need to be right without someone asking the right question at the right time.
What Sidekick does well
- It's included. Sidekick comes with Shopify, so there's nothing to install or pay for.
- It answers in plain language. Ask "What should I reorder?" and Shopify says it recommends products based on your sales data, what you have left, and a demand forecast.
- It drafts the purchase order. Shopify says Sidekick can create a purchase order pre-filled with products, quantities, and cost prices, and you can adjust it by chatting.
- It covers more than reordering. Sidekick can help with transfers between locations, slow-moving stock, and questions about any of your store data.
Where Posto goes further
- It doesn't wait to be asked. Posto checks every product every day, and optional daily or weekly emails list what's at or below its reorder point.
- Supplier rules are built in. Posto stores each supplier's lead time, minimum order, and case pack, and rounds every order to them. Once 3 orders from a supplier have arrived, it times orders by how long deliveries actually took. Shopify's own migration guide says these details can only live in metafields, which purchase order calculations don't use.
- The math is on the page. Every Posto recommendation shows its working, the same way every time. We couldn't find Shopify documentation describing how Sidekick calculates its recommendations.
- Peaks are planned for. Posto builds in Black Friday and the holiday peak, and leaves stockout days out of demand.
- It sends the order. Posto emails the purchase order to your supplier with the PDF attached. Shopify's guide says you can't email a purchase order from the Shopify admin, only download the PDF.
- It works out what each unit really cost. Posto spreads freight, duty, and fees into a landed cost per unit, and if you turn it on, updates Shopify's cost per item when stock arrives. Shopify's guide says cost per item stays fixed when you receive stock and points to third-party apps for landed cost.
Where Sidekick is ahead
- No extra app, and no extra cost.
- Locations. It can suggest how to rebalance stock between locations. Posto forecasts store-wide.
- Shopify's own purchase orders. Sidekick works with Shopify's built-in purchase orders, transfers, and POS receiving.
- Any question. It can answer questions about sales, products, and customers that a reorder tool doesn't cover.
Can you use both?
Yes. Many stores will keep asking Sidekick questions either way. Just pick one place for purchase orders: Posto keeps its own and doesn't read Shopify's, so running the same order in both means tracking it twice.
Sources
Shopify Help Center, Migrating from Stocky to Shopify inventory management, and the Shopify blog, Managing inventory in Shopify just got easier, checked October 2 and 3, 2026. Shopify updates Sidekick often, so check the linked pages for the latest.