Best Shopify Back-in-Stock Apps for Size Restocks

The best Shopify back-in-stock app for a clothing store is one that alerts shoppers per size variant, not per product. This guide compares three options from the Shopify App Store (checked November 2026) and shows what to test before you commit.

Size restocks are different from other restocks. A shopper who wants a medium does not care that the large is back. If you also run a virtual try-on app on Shopify, shoppers will often find their size first and discover it is sold out second, which makes size-level alerts more important.

Why do size restocks need their own alerts?

Clothing sells out unevenly. The middle sizes go first, and the extremes sit on the shelf. A generic "notify me" button that tracks the whole product sends the wrong message to many people.

A good size restock flow does three things:

• It records which variant the shopper asked for.
• It sends the alert only when that variant has stock again.
• It gives you a count of waiting shoppers per size, so you can plan reorders.

That last point is the most useful for a fashion store. Waiting lists are demand data you did not have to buy.

Which back-in-stock apps are worth comparing?

The three listings below were read on the Shopify App Store in November 2026. Plans and prices change, so confirm them on each listing before you install.

App	Alert channels (per listing)	Free plan	Variants
Amp Back in Stock & Preorder +	Email, SMS and push	Yes, 10 notifications a month	Reviewers say it works well with variants
Notify-me - Stock and Price	Email, SMS, WhatsApp or custom, through Shopify Flow	Yes, 100 alerts a month	Not stated on the listing
Klaviyo: Email Marketing & SMS	Email and SMS	Yes, up to 250 active profiles	Not stated on the listing

Prices and limits come from each app's own listing page. Checked November 2026.

Amp Back in Stock & Preorder +

The listing says the app sends back-in-stock alerts by email, SMS and push, supports preorders, and shows low stock badges. It offers a free plan, and paid plans start at $19 a month on the listing, with higher tiers adding more notifications and integrations. The listing says it is built for high-SKU catalogs, which suits stores with many size and color variants.

Notify-me - Stock and Price

The listing describes back-in-stock and price-drop alerts that connect to Shopify Flow, so you can send alerts by email, SMS, WhatsApp or other automations. Paid plans start at $9.90 a month. It is a newer listing with no reviews yet, and it does not say whether variants are supported, so test that yourself first.

Klaviyo: Email Marketing & SMS

Klaviyo is a full email and SMS platform, and the listing names back-in-stock emails among its campaign types. It makes sense if you already send your campaigns there. If you do not, a dedicated restock app is usually quicker to set up.

What should you test before installing?

Run this checklist on a development store or a single product:

1. Mark one size of a test product as out of stock.
2. Sign up for an alert on that size from a phone.
3. Restock a different size and confirm no alert is sent.
4. Restock the size you signed up for and confirm the alert arrives, with a link to the right variant.
5. Check that the report shows waiting shoppers by size.

If an app passes steps 3 and 4, it handles sizes properly. If it sends an alert for any restock, shoppers will start to ignore your emails.

How do you pair restock alerts with accurate sizing?

Restock alerts only help if the shopper picks the right size in the first place. A shopper who buys the wrong size and returns it costs you twice.

A body-scan size recommendation shortens that path. The size chart matching setup shows how the recommendation uses your own labels, so the size a shopper is told about is the same size they can subscribe to on the restock form. For the wider question of tools, see size charts versus size recommendations.

Plus-size ranges often sell out at the edges first, so it helps to design for them from the start. The guide on Shopify themes for plus-size fashion covers how themes show extended ranges.

How should you word a size restock message?

Keep the message short and specific. The shopper asked about one size of one product, so say exactly that.

A good restock message includes:

• The product name and the size, such as "Linen shirt, size M".
• A direct link to that variant, so the size is already selected.
• A plain line on how limited the stock is, only if it is true.
• Your fit note, if the item runs small or large.

Avoid inventing urgency. If you have no real stock count, do not claim the size is almost gone. A fashion store depends on trust, and one false "last chance" message costs more than it gains.

How do you use waiting-list data to plan reorders?

Every sign-up is a shopper telling you which size they wanted and could not buy. That is useful demand data, even before a single sale.

Once a month, look at the waiting list by size:

1. List the products with the most sign-ups.
2. Check which sizes those shoppers asked for.
3. Compare that to your next production or reorder run.
4. Note any size that always has a long list, since your size run may be too narrow there.

If one size always sells out, your size chart or ordering plan may need a fix. The same sizes may also be the ones with the most fit-related returns, so look at both lists together.

How do you decide which app to choose?

Pick on the answers to these questions, not the star rating:

• Does it track alerts per variant?
• Can the shopper choose email, SMS or WhatsApp?
• Is the monthly alert limit enough for your busiest launch week?
• Does it show waiting shoppers per size?
• Does it work with the theme you run now?

Start on a free plan if one is offered. Move up only when you hit the alert limit.

FAQs

Can a back-in-stock app alert shoppers for one size only?

Yes, if the app tracks variants. Test it as in the checklist above, because not every listing states variant support.

Do back-in-stock apps work with preorders?

Some do. The Amp listing, for example, says it supports preorders. Check the listing of any app you consider.

Should I use SMS or email for restock alerts?

Email is cheaper and fine for most stores. SMS is faster for popular sizes that sell out again quickly, but the cost depends on the app and the country.

Does ZeDaq.ai send restock alerts?

No. ZeDaq.ai is an AI virtual try-on and size recommendation app, so it does not replace a back-in-stock app. It helps shoppers choose the right size before they order.