A Shopify back-in-stock alert collects an email for one variant and sends that person an email when the variant's available quantity crosses a stock threshold you set. In SK Back In Stock, that message is email. The catalog does not include SMS, a WhatsApp restock note, or a preorder button. The App Store listing shows the price as Free.
The shopper does not place an order by joining. They leave an address for a size, color, or other variant that is currently unavailable. You get a list of people who asked to hear about that variant, and they get one restock email when inventory crosses the line you configured. The default threshold in the catalog is 1.
What the shopper does
On the product page, a Notify Me button is meant for the variant that is sold out. The App Store listing describes that button taking the place of Add to Cart in the sold-out state. The app catalog describes the button's visibility following the variant selected on the page, updating when the shopper changes size or color, without a full reload.
The signup stores an email. It also stores the shop, the product and variant IDs, the product title, handle, and image, an alert type, a status, and a consent timestamp. Status can be waiting, notified, purchased, or unsubscribed. The catalog does not say the shopper must log into a customer account before joining.
Client-side and server-side checks both validate the email. A second signup from an address that is already waiting can be answered with the popup's already-subscribed message, which you can edit.
- Email only: the catalog's signup field is an email address, not a phone number for a text message.
- One variant: the row keeps both the product ID and the variant ID, so a medium is not the same waitlist as a large.
- Consent time: the signup stores when the person agreed to the alert.
What you configure
You place the button with a theme app block on the product template, or with a global app embed. A configuration can apply to all products, to specific collections, or to specific products, and it can exclude products. More than one configuration can exist on the same shop. Targeting a collection limits which products use that configuration. It is not described as a Notify Me button on the collection grid itself.
Restock detection listens to Shopify's inventory levels update webhook. On each event the app resolves the inventory item to its variant, compares the new available quantity with the last known quantity, and sends only when the quantity crosses your threshold. If a variant is already above that line and you add more units, the catalog says that further restock does not fire another alert. The same crossing idea, inverted, can power an optional low-stock alert. That is a separate alert type, not the back-in-stock email.
The webhook does not send the email itself. It writes a row to an email queue and returns. A worker later renders your subject and body and sends through a rate-limited mail connection. Failed sends retry with backoff, up to five attempts, and then the job is marked permanently failed. You can send yourself a test of the template. The catalog does not promise a delivery time, so do not tell shoppers the note will arrive within a set number of minutes.
The template placeholders documented in the catalog are product name, product URL, new price, and old price. Dynamic values are escaped before they go into the message. There is no documented discount code in that template.
Variant-level demand
Every signup, every inventory check, and every notification target is stored at variant level. The admin list can roll those rows up so you see a product, and you can still open the variant, the email, the subscribed date, the status, and the notified date. Search and status filters sit on that list.
That split matters for apparel and any product with options. Twenty people waiting on one color is a buying signal for that color. It is not a reason to reorder every color on the product. The dashboard's top line shows total signups, alerts sent, and a purchased count. Those three numbers answer different questions. Signups are requests. Alerts sent are emails the queue attempted. Purchased is a later match, not the signup itself.
What this alert is not
An email waitlist does not charge the shopper, reserve a unit, or take a deposit. It does not create a draft order. It does not push the address into Klaviyo, and it does not send the restock note through WhatsApp. SK Back In Stock's catalog is the email path above. If your requirement is a text message, a WhatsApp alert, a preorder, or a Klaviyo flow, this app's current documentation does not cover that job.
The App Store listing shows the price as Free and lists no paid plans. Neither the listing nor the catalog states a monthly email cap, so do not describe the app as unlimited. Check the live listing for any pricing change before you install.
A customer redact request anonymizes matching signup emails and cancels pending notification jobs. That is a privacy task, not a second marketing channel.
How to read it after 30 days
The dashboard includes a 30-day signup growth percentage, a delivery rate of sent versus failed, and revenue recovered. Use the catalog's definition for that revenue figure: it is the sum of line-item value for signups later matched on the orders-create webhook by the same email and the same variant. It is not a second formula, and it does not prove the email caused the order. Someone can buy the variant without opening the message. Someone can open the message and buy a different size, and that purchase would not match this rule.
After a month, ask which variants collected signups, whether alerts failed, and which notified people later bought that same variant. Growth percentage is not a sales forecast.
Questions merchants ask
Does the shopper need an account?
The documented signup is an email for a variant, plus a consent timestamp. The catalog does not describe a customer-account requirement.
Is the restock email instant?
No delivery-time promise is in the catalog. The inventory webhook queues the job. A worker sends it, and a failed send can retry up to five times.
Will adding stock to an in-stock variant email everyone again?
Not by the crossing rule. The alert fires when available quantity crosses your threshold. Stock that is already over the line, and then increases, does not re-trigger the back-in-stock send.
Read the current scope on SK Back In Stock before you install it. The job it documents is a variant email when stock crosses your threshold.