A Shopify back in stock app adds a Notify Me button to sold-out products and messages the shopper when stock returns. Choose by how many alerts you'll send each month, which channels you need (email, SMS, push or WhatsApp) and whether you also want preorders or price-drop alerts.
Six of the eight apps on this page stop their free plan at 10 notifications a month; the other two allow 50 and 100. That one number decides more than any feature list, so start there.
Do the sum before you pick
Here's a worked example with round numbers. Say you sell 120 products, and in a normal month 30 variants sell out. If each sold-out variant collects 15 sign-ups before it comes back, that's 450 people waiting. When the delivery lands, the app needs to send 450 alerts in one go.
A plan capped at 10 alerts a month sends the first 10 and leaves 440 people who asked to hear from you in silence. That's worse than having no button, because you collected their address and then ignored them.
So, before you look at a single app, open Products in your Shopify admin, filter to items with no stock, think back over the last three months, and estimate the waiting list. Then pick a tier that covers your busiest month, not your average one. Tiers in this category step by alert volume (one app runs 100, 1,000 and 3,000 alerts a month before unlimited), so the number you land on tells you which tier to read.
If you don't know how fast things sell out, your stock tool is the place to find out; our guide to Shopify inventory management apps covers tools that report it.
Email, SMS, push or WhatsApp
Every app on this list sends email. The question is whether you need more.
SMS is the channel I'd add for limited drops, where a few hours' delay can mean the stock's gone again. It's billed on top of the plan: one app prices SMS by destination country, and another quotes 5 to 40 cents a message depending on length. If you sell abroad, the same alert costs different amounts to different shoppers, so cap SMS to your main markets or to high-value products.
Push and WhatsApp suit stores whose shoppers already use them with you. If your customers have never opted into browser push or never message you on WhatsApp, adding the channel won't change much.
A sensible rule: email for everyone, SMS only where the margin covers the message, and nothing else until a test shows it pays.
Email-first alert apps
SC Back In Stock
Out-of-stock products get a Notify Me button and the restock email goes out on its own; it comes from the Shop Core group of apps.
Restock Alert by StoreBuddies
Shoppers sign up on the exact variant they want, then receive a branded restock email, and price-drop alerts sit alongside.
Notify-me - Stock and Price
Stores that run Shopify Flow will like this one: back-in-stock and price-drop sign-ups fire Flow events you can build on.
ReStocked
Automates customer restock alerts, adds reporting, and has an SEO booster on its Pro plan for out-of-stock pages.
Alerts across more channels, with waitlists and preorders
Amp Back in Stock & Preorder
One app for email, SMS and push restock alerts that also handles preorders and low-stock badges on the product page.
Notify Me! Back in Stock Alert
Turns a sold-out product into a waiting list, then alerts by email, SMS, push or WhatsApp; preorders and wishlists come in the same app.
Back In Stock Alerts by H3
Restock notifications over email, SMS and WhatsApp for stores whose customers live on their phones.
Appikon Back In Stock
Waitlists plus automatic alerts by email and SMS, connecting to Mailchimp and Klaviyo so sign-ups reach your main list.
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Single-job alert or a wider stock-demand tool?
A few apps here combine back-in-stock with preorders and wishlists. That's a different purchase. You're no longer buying an alert, you're choosing how you handle demand for anything you can't ship today.
Go wide if you regularly take orders before stock arrives, sell made-to-order items or run seasonal launches. Stay narrow if sell-outs are occasional and you'd rather not change how checkout works. Taking money before you can ship brings its own questions about delivery dates and refunds, and our guide to Shopify pre-order apps covers that side.
Price-drop alerts are the other add-on worth knowing about. Some entry plans include them. They're handy if you run sales, but they also teach shoppers to wait, so switch them on deliberately.
Where these apps go wrong
The alert lands in the wrong voice. Whatever the default template looks like, spend ten minutes on it: your logo, the product image, one button straight to the variant, and a subject line naming the product.
Everyone gets told at once for a tiny restock. If 450 people are waiting and you've received 40 units, a blast to all of them creates 410 disappointed shoppers. If your app can't send in batches, keep the product marked sold out until you've got enough to go round.
The list stays in the app. A shopper who asked to hear about a product is warm. If the app doesn't pass them to your email platform, you lose that signal. Check the integrations, and if you're still choosing an email tool, our guide to email marketing for Shopify compares them.
The button sits under the fold. On mobile, a Notify Me button below the description gets missed. Put it where the Add to cart button would be.
Do you make Shopify back in stock apps? Tool makers can ask to be considered for a featured place on this list.
What the bill looks like
Read across the eight listings and the first paid tier lands anywhere from $4 to $19.99 a month. Where a listing states it, that first tier buys between 100 and 500 alerts a month, and higher tiers step up by alert volume. All eight have a free plan, so the only cost of the sum above is twenty minutes.
SMS is the line that moves. Because it's charged per message on top of the plan, a 450-person waiting list on SMS can cost more in one evening than the app does in a month. Price that before you switch it on for everyone.
Four stores, four answers
A candle shop that sells out twice a year. An email-only app on its first paid tier is plenty. The free tier stops being useful the first time more than a handful of people wait for the same scent.
A streetwear brand with weekly drops. Add SMS, cap it to your home market, and keep email for everyone else.
A furniture maker that already takes orders before stock lands. Pick one app that does back-in-stock and preorders together, so customers get one set of emails and you keep one dashboard.
A store running Shopify Flow and a big email platform. Choose on integrations first. The alert is the start of a sequence here, not the end of one.
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