The "Notify me when back in stock" button is not a standard feature in Shopify. Many articles have covered this point.

What's more complicated is that Shopify Flow has the Product variant back in stock trigger, which was added on August 25, 2023. This trigger fires when the inventory of a variant goes from negative to positive. Merchants who find this trigger might naturally think, "Then, I can use Flow to set it up."

However, they can't. The reason is not a functional deficiency but a more structural issue. The data that identifies "customers waiting for the product" is not stored anywhere in Shopify. The trigger fires, but there is no recipient to send to.

This article will identify the points at which custom solutions fail by checking the official documentation for Flow, Shopify Forms, Shopify Messaging, and the Dawn theme. It will also clarify the issue of inconsistent pricing denominators when comparing back-in-stock notification apps. The investigation was conducted on September 1, 2026, with all prices in USD as listed on the Shopify App Store.

Conclusion

If your store experiences stockouts only a few times a month or has a limited number of SKUs, you don't need an app. You can use the Product variant back in stock trigger in Flow and the Send internal email action to notify the relevant staff, and handle it manually.

If you operate backorders (selling while out of stock), consider redesigning your process as a pre-order. Klaviyo's Back in Stock does not work as intended in stores that allow sales while out of stock.

If you are already using Klaviyo, Klaviyo's Back in Stock flow can handle everything. Adding a dedicated app is generally unnecessary. However, Klaviyo's Back in Stock form can only be created once per account, and A/B testing is not possible.

If you want a back-in-stock notification app in Japanese UI and at a low cost, consider Back In Stock, Notify Me: Kbite ($5 for 500 emails, $9 for 2,500 emails). For a monthly notification volume exceeding a few thousand emails, consider SC Back in Stock Notify Me ($10 for unlimited emails). For combining back-in-stock notifications and pre-orders, consider Preorder, Back In Stock - STOQ. For notifications via LINE, consider Amp Back in Stock & Preorder + CRM PLUS on LINE or Privacy Back in Stock.

In all cases, you need to have your store's numbers ready before comparing. The reasons are explained in the latter part of the article.

What Shopify Can Do: Detection Only

First, let's accurately identify what can be done.

The Product variant back in stock trigger in Shopify Flow fires when the inventory of a variant goes from negative to positive, regardless of the reason. It can be triggered by order cancellations, manual changes in the admin, or updates from inventory management apps. If you want to track by location, there is also the Product variant inventory quantity changed trigger.

After the trigger fires, there are still things you can do. You can automatically relist the product, add tags, add it to a collection, or update metadata. And you can send an internal email to staff.

In other words, you can fully automate the detection of stock restoration without any additional costs. For stores with stockouts only a few times a month, stopping here and handling it manually is the most reasonable approach.

Two Points Where Custom Solutions Fail

Failure Point 1: Trigger Does Not Have a Customer List

The Shopify Help Center page for the Product variant back in stock trigger lists the data it passes to the workflow. The only data passed is productVariant.

The list does not include a list of email addresses of customers waiting for the product to be restocked. This is because the data that records when a customer has clicked "Notify me when back in stock" on the product page does not exist in Shopify's standard features.

The trigger fires, but there is no recipient.

Failure Point 2: Flow Does Not Have an Action to Send Emails to Customers

Even if you have a subscriber list, the next hurdle is that Flow's action list does not include an action to send marketing emails to any customer. The only action available is Send internal email.

And the official documentation for this action states the following:

You can't use variables to customize the email address to which the message is sent.

This means the recipient address is fixed, and individual segmentation is not possible.

The Send internal email action is best used to send emails to staff. To automate emails to customers, create a marketing automation.

It also states that marketing automation should be used for customer emails.

As a side note, the Flow template library has a "Get notified when demand increases for out-of-stock products" template. However, its description is "an out of stock item has 10 customers waiting for it to be restocked through Back in Stock," which assumes that a third-party app is holding the subscribers and notifies the merchant. Even official templates assume that "subscribers are held by the app."

Shopify Forms and Shopify Messaging Do Not Fill the Gap

Following Flow's advice to use "marketing automation," we can look at Shopify Messaging (formerly Shopify Email). However, it also stops here.

The automation you can create with Shopify Messaging, as documented, falls into four categories: abandoned cart, welcome, post-purchase (thank you, upsell, win back), and special occasions (birthday, VIP). There is no automation based on stock levels.

Shopify Forms also do not help. Forms are available in two types: pop-ups and inline. Their uses include marketing sign-ups, B2B lead applications, customer data collection, and inquiries. There is no concept of triggering a send based on stock status. Additionally, there are limitations: up to 25 forms per store, 31 fields per form, no branching, and no multi-step forms.

Even if you place a Forms on an out-of-stock product page, you can collect email addresses. However, there is no association between who is waiting for which product variant, and no automatic send at restock. After collecting, you will need to manually match and send.

Another common misconception is that "Dawn has a back-in-stock notification button." Searching locales/en.default.json in the Dawn official repository shows no translation keys for notify, back_in_stock, or restock. The only keys are sold_out (Sold out) and unavailable, which display labels, not buttons.

Note that with a plan above Grow, you can use the Send HTTP Request action in Flow to send a restock event to an external service. However, you will need to create your own UI for collecting subscribers, storing them, sending emails, handling opt-outs, and multi-language support. This is equivalent to creating a back-in-stock notification app.

The Real Comparison Problem Is the Billing Metric, Not the Price

This is the most important part of this article.

There are already many articles comparing back-in-stock notification apps. However, most of them use the phrase "A has a free plan, B starts at $19." This comparison is invalid because the pricing denominators are different for each app.

As of September 1, 2026, there are 282 apps in the "Stock alerts" category on the Shopify App Store. When categorized by pricing denominator, at least six types can be identified.

App	Denominator	Free Plan Cap	Minimum Paid Plan
Back In Stock, Notify Me: Kbite	Number of sent email notifications per month	30 emails/month (subscribers have unlimited)	$5 = 500 emails/month
Amp Back in Stock & Preorder +	Number of sent notifications per month	10 notifications/month (sign-ups are unlimited)	$19 = 500 emails/month
SC Back in Stock Notify Me	Unlimited emails, SMS only by volume	50 emails/month (requests are unlimited)	$10 = unlimited emails
Swym Back in Stock Alerts	Number of registration requests per month	None	$19.99 = 1,000 requests/month
Preorder, Back In Stock - STOQ	Number of preorders and emails/SMS	10 preorders + 30 emails/month	$10 = 100 preorders + 1,000 emails
Notify Me! Back in Stock Alert	Number of notifications, preorders, and wish list actions	10 notifications + 5 preorders + 50 actions	$9.90 = 500 notifications + 500 preorders + 2,000 actions
Preorder Now Presale Timesact (Fixed)	Shopify plan hierarchy	—	Basic $23 / Grow $47 / Advanced $73 / Plus $117
XFlow Back in Stock Alert	Revenue generated through the app	5 orders (emails and sign-ups are unlimited)	$9 = revenue up to $1,000, +$7/$1,000 over
Klaviyo	Active profiles multiplied by sent emails	250 profiles / 500 emails/month	$20 = 500 profiles / 5,000 emails
Back-in-Stock Notification	Email quota and SMS/Line quota (separate)	None	$9 = 1,500 emails / 50 SMS/Line

Four key points can be derived from the table:

"Free plan" designation is useless for horizontal comparison. The free plan cap ranges from "30 emails/month" (Kbite) to "unlimited emails" (XFlow, Timesact), differing by two orders of magnitude. Every time you see a number like 10, you must determine whether it refers to 10 notifications, 10 sign-ups, or 10 pre-orders to make a comparison.

The point of charging is either at the entrance or at the exit. Swym charges based on "alert requests = sign-up registration requests," while Kbite and Amp charge based on "number of sent notifications." These two methods can result in different calculations even for the same monthly volume. For stores with limited products or seasonal items, where sign-ups accumulate but restocks are rare, the Swym model is less advantageous. Conversely, for stores with frequent restocks and large individual notifications, the exit model is less advantageous.

Apps with pre-order features have multiple-axis denominators. STOQ, Notify Me!, REZ, and Timesact may require paying for the pre-order slot even if you only use restock notifications. You must estimate which slot will run out first.

Only the TIMESACT CORE Fixed plan is priced based on the store's Shopify plan hierarchy. The same functionality and usage can result in a price difference of about 5 times between a Basic store ($23) and a Plus store ($117). No other app in the checked range uses this pricing method.

Three Numbers Needed to Compare Apps with Different Denominators

To make a fair comparison, you need to provide the following three numbers for your store:

• A: Monthly "Back in Stock registration" count (entrance volume) – Swym model denominator
• B: Monthly "sent notifications" count (part of A, only for those who restocked that month) – Kbite, Amp, SC model denominator
• C: Monthly sales revenue through restock notifications (exit amount) – XFlow model denominator

A and B do not match. If restocks are delayed, A accumulates while B remains at 0. Without these three numbers, a monthly-only comparison is meaningless.

What Are You Paying For?

Another perspective to consider is that Shopify Messaging allows up to 10,000 emails per month for free, with an additional cost of $1 per 1,000 emails. Thus, sending emails is essentially free within Shopify.

The monthly cost paid to back-in-stock notification apps is not for sending emails. It is for the system that retains which customers are waiting for which product variants, detects restocks, and sends notifications to those customers only. Understanding this structure clarifies why the free plan cap can be "30 emails" or "unlimited emails" depending on the app.

Japanese UI and Japanese Support Are Separate Issues

In the Stock Alerts category, all top 24 apps are developed overseas. Kbite (India), STOQ (US), Timesact (Romania), and REZ (Vietnam) provide Japanese UI management interfaces, but whether they offer Japanese support is a separate issue. In this survey, we could not confirm the Japanese support status for these apps.

Three apps developed in Japan were confirmed: Back In Stock Japanese Version: Restock Notification Supporter (Netyear Group Corporation, 4.0/3 reviews), Privacy Restock Notification (Wilico, Inc., 5.0/10 reviews), and StoreCRM (GroovyMedia Inc., 5.0/16 reviews). All are Japanese-only apps, and Japanese support is expected. However, the low number of reviews (3, 10, 16) should be considered when compared to top apps (over 3,000 reviews).

Important note on StoreCRM

For StoreCRM, one important note is that back-in-stock notifications are only available on the Pro plan at $100+/month or the LINE plan at $65+. Back-in-stock notifications are not available on the free-to-install plan.

For back-in-stock notifications via LINE, the Social PLUS "CRM PLUS on LINE" does not collect requests on its own. The official manual states that "it must be linked with the Shopify app 'AMP - Back in Stock' to send back-in-stock notifications via LINE." A two-app installation is required. Privacy Restock Notification has separate email and SMS/Line quotas from the start.

All apps checked in this survey were priced in USD. No app with a yen pricing plan was found, including those developed in Japan.

Using Klaviyo

There is no explicit minimum plan requirement for Klaviyo Back in Stock, as stated in the official documentation. The only prerequisite is "Shopify or BigCommerce."

The practical constraint is not the plan but the capacity. The free plan allows 250 active profiles and 500 emails/month. The first paid tier is $20/month (500 profiles/5,000 emails).

On the other hand, there are three clear functional constraints:

• Only one Back in Stock form can be created at a time (including drafts). You cannot differentiate by multiple brands or designs.
• No A/B testing is possible.
• Notification control settings (how many items to notify, how many people per item, batch intervals) are set at the account level and apply to all Back in Stock flows.

The most overlooked technical requirement is that you must disable "Continue selling when out of stock." If enabled, the app treats out-of-stock items as in stock, hiding the "Notify Me" button and form, and no notifications are sent. This conflicts with back-order operations.

However, there are also benefits. Klaviyo retains synced profiles even if the app is uninstalled or disabled. You do not have to worry about handling subscriber data when you cancel the app.

What Happens to Subscriber Data When You Uninstall?

This varies by app and is not mentioned on the App Store page. You need to check the privacy policy.

Swym states that it may retain personal data for up to 365 days after the client stops using the service unless a deletion request is made. This is the most explicit statement. It also notes that manual deletion of swym-related code in the theme's layouts/snippets is required after uninstallation.

Notify Me! states that it may retain personal data indefinitely after the client stops using the service unless a deletion request is made.

For STOQ and Amp, the number of days of retention after uninstallation could not be confirmed.

A common misconception to correct is the "48-hour rule" that app data will be deleted. The correct interpretation is that 48 hours is the timing for the shop/redact webhook to be sent to the app. The developer's deletion obligation is to complete it within 30 days of receiving the webhook. The data does not automatically delete within 48 hours.

Case-by-Case Selection

Apps are not needed: For stores with a few stockouts per month, a small number of SKUs, or no stockouts at all (made-to-order). Use Flow to notify staff manually.

Already using Klaviyo: Use Klaviyo's Back in Stock flow. However, it must meet the conditions of one form, no A/B testing, and "Continue selling when out of stock" must be off.

Only back-in-stock notifications, Japanese UI, and low cost: Back In Stock, Notify Me: Kbite. $5 for 500 emails, $9 for 2,500 emails. All plans have unlimited subscribers. However, it does not include preorder functionality.

Monthly notifications in the thousands to tens of thousands, email-centric: SC Back in Stock Notify Me. $10 for unlimited emails. However, consider the lower rating of 4.5 (158 reviews) compared to the top apps' 4.9-5.0.

One app for back-in-stock notifications and preorders (deposits, installment payments): Preorder, Back In Stock - STOQ. It has a Japanese UI, supports both Checkout and POS extensions, and offers the most payment options. However, CSV export is a paid feature.

Back-in-stock notifications, wish lists, B2B preorders, and new customer account integration: Notify Me! Back in Stock Alert. However, the free plan is limited to 10 notifications, and pricing depends on three metrics.

Using Bloomreach, Ometria, Sailthru, or Listrak? The most integrations with external ESPs are with Swym Back in Stock Alerts. There is no free plan.

With Noshi-like Japanese-specific operations, and LINE delivery required: The combination of Amp Back in Stock & Preorder + and CRM PLUS on LINE, or Klaviyo back-in-stock notifications.

Pre-Installation Checklist

• Count the frequency of stockouts and SKU numbers to determine if an app is necessary.
• Calculate the monthly registration count (A), monthly send count (B), and sales through notifications (C).
• Determine which of A, B, or C is the denominator for the app under consideration.
• Confirm the number of free plans (X) for the app.
• Ensure that the subscription order does not include a charge for preorder slots if the app does not require preorders.
• Verify the cost per transaction for SMS/LINE if using them.
• Ensure that the setting to continue selling even when out of stock does not conflict with the app's functionality (especially for Klaviyo).
• Confirm how subscriber data is handled upon uninstallation in the privacy policy.
• Evaluate the app with separate consideration for Japanese UI and Japanese support.
• Confirm whether widget reconfiguration is needed when changing themes.

Summary

When it comes to back-in-stock notifications, there are four key criteria to consider.

1. Shopify's native feature only allows the store to know when stock is back in. Structurally, it cannot send notifications because there is no place to store subscriber data. The fact that a trigger exists in Flow does not mean it can be done.
2. Before comparing monthly costs, ensure the denominators are aligned. There are over five different denominators: send count, registration count, pre-order count, sales, and your Shopify plan tier.
3. Present your store's A (registration count), B (send count), and C (sales through notifications) first. Without these, it's impossible to determine which denominator is most advantageous.
4. Japanese UI and Japanese support are separate considerations. Most apps with a Japanese UI are developed overseas, and we were unable to confirm the availability of Japanese support.

The next step is to count the number of stockouts in the last three months and the number of those that actually restocked. At this point, the number of candidates will naturally be reduced to two or three.

Note that the cost, number of reviews, and official app names can vary. The numbers in this article are based on direct confirmation from the Shopify App Store and official pages of each developer as of September 1, 2026. Please check the latest information before installation.