Best Shopify Back-in-Stock Apps: Top 6 Picks Thoroughly Reviewed

Every time a product goes out of stock, potential revenue walks away with it. A Shopify back-in-stock app helps you capture that lost demand instead of letting it disappear.

Most stores lose sales not because customers aren’t interested, but because there’s no way to bring them back at the right moment. A simple “Notify Me” flow fixes this by collecting emails or phone numbers and sending alerts when inventory returns.

But in reality, the best back-in-stock apps for Shopify are not all the same. Some focus on simple alerts, others on automation, multi-channel messaging, or preorder workflows. From our experience reviewing multiple Shopify back-in-stock app options:

• XFlow stands out for automation
  
• Notify! and STOQ for multi-channel and preorder use cases
• REZ for free all-in-one basics
• Amp is strongest for scale and controlled delivery.

In this blog, we break down the best options so you can quickly find the right Shopify back-in-stock app for your store size and needs.

Top 6 Shopify Back-in-Stock Apps: In-Depth Comparison of Features and Pricing

1. XFlow Back in Stock Automation

Pricing: Currently free

XFlow introduces a totally new logic that lets you build hyper-customized campaigns, design unrestricted email layouts from scratch, and map out unique paths for every single product or inventory scenario. This flexible, workflow-driven framework offers advanced automation capabilities that merchants can currently use entirely free of charge.

Image source: XFlow on Shopify App Store

What Makes XFlow Unique?

XFlow introduces a total new logic to back-in-stock management by separating the entire process into three clear, decoupled layers:

• Campaigns (defining which products or collections are included)
• Workflows (defining what happens behind the scenes when stock returns)
• Emails (defining how the final message is styled and delivered)

Image source: XFlow

To power this ecosystem, XFlow is the only back-in-stock app built entirely around a node-based workflow automation engine (similar to logic structures found in n8n or Shopify Flow). Instead of forcing you into rigid, pre-set alerts, this architecture empowers merchants to construct fully customized communication paths using three simple, intuitive building blocks:

Image source: XFlow App Listing

Core Trigger Types & Marketing Capabilities

By leveraging logic-driven paths, you can easily deploy tailored campaigns across multiple scenarios:

• Trigger 1 Product Restock - Back-in-Stock Alerts: Instantly and automatically dispatch notifications to waitlisted customers the moment inventory refills.
• Trigger 2 New Form Sign-up - New Subscriber Welcome: Automatically drop a welcome email containing a unique discount code right after a shopper interacts with your "Notify Me" form. It goes beyond standard customer alerts by setting up conditions to notify your internal team when VIP customers sign up for restock notifications.

Moving away from rigid, back-in-stock systems doesn't just save time, XFlow completely changes how you capture high-intent buyers. By embedding an advanced automation engine directly into your store, you can replace generic notifications with targeted, behavior-driven paths.

• Hands-Off Efficiency: Once your automated paths are active, the system runs independently without requiring manual list tracking or manual email dispatches.
• Precision Timing: Deliver critical inventory alerts when engagement intent and buying probability are at their highest.
• Tailored Personalization: Deploy conditions to isolate and trigger unique messaging tracks based on user behavior, historical purchases, or preferences.
• Frictionless Scaling: The architecture handles data loads efficiently whether managing 10 or 10,000 active subscribers.
• Full Log Transparency: Audit specific execution logs to review exactly how paths run, track message success, and optimize conversion flaws.

Next-Level Email Design Freedom

Unlike traditional back-in-stock apps that lock you into rigid templates with fixed subject, header, or body inputs, XFlow gives you complete design control. The template editor leaves everything blank by default, empowering you to build fully branded layouts from the ground up using drag-and-drop content blocks.

Streamlined Subscription & Waitlist Management

XFlow includes a dedicated Subscription Management panel that gives you complete visibility and control over your restock data:

• Granular Filtering: Easily sort and filter your subscriber database by specific criteria, such as product variants, specific dates, channel type (Email vs. Web Push), or alert status.
• Manual Notification Overrides: Take manual control over your restock dispatches by instantly executing batch sends or custom alert overrides directly from your waitlist table.
• Demand & Intent Tracking: Gain immediate, actionable insight into which out-of-stock products or specific variants are generating the highest customer demand, allowing you to optimize your manufacturing and restocking priorities.

Image source: XFlow

Best for: Scaling Shopify brands with large SKU catalogs or multi-product collections that have outgrown rigid, store-wide restock rules. It is the ideal choice for high-volume merchants who need precise, product-level control to protect their revenue when hero products go out of stock, as well as established DTC stores looking for an advanced conversion rate optimization (CRO) layer to capture every ounce of earned customer demand.

2. Kbite - Back In Stock, Notify Me

Pricing: Free plan available + paid tiers

• Basic: $5/month
• Starter: $9/month
• Pro: $19/month

Kbite bundles price drop and back-in-stock alerts into a single app, delivering them via both email and SMS, all at a highly economical price point backed by an extensive pool of customer reviews that are 99% positive.

Image source: Kbite on Shopify App Store

Kbite keeps its setup simple but powerful, allowing you to define exactly when and how customers receive "back in stock" alerts. You can customize your entire automated recovery sequence in just a few clicks:

• Design Your Touchpoints: Quickly edit the "Notify Me" button and its pop-up registration form to match your brand's aesthetic perfectly.
• Acknowledge Sign-ups: Customize the "Post-Form Submission" message to immediately thank customers for subscribing.
• Craft the Perfect Alert: Design the automated back-in-stock email template so it is ready to send the moment your shelves are restocked. 

Image source: Kbite

Once your design is ready, Kbite gives you precise control over exactly when those automated alerts are fired. To protect your customer experience and avoid sending confusing emails, KBite handles advanced inventory scenarios with 3 core rules based on your "track quantity" and "continue selling" settings:

Image source: Kbite

Additionally, you can fine-tune your launch timing with the Minimum Stock Threshold Safety Net. This setting lets you choose exactly how many items must be back in stock before an email fires. While setting this to 1 triggers alerts instantly upon restocking a single item, you can set it higher to ensure you have enough inventory to actually meet sudden high demand.

Beyond precise restock timing, you can expand your store's reach and convert high-intent shoppers with other built-in features:

Other features:

• Recover Lost Revenue via Price Drops: Automatically re-engage window shoppers the moment a product goes on sale. This feature targets price-sensitive buyers who showed interest but hesitated at checkout, turning stagnant inventory into quick sales.
• Instantly Reach Buyers via SMS: If you want to cut through crowded email inboxes by sending instant text alerts directly to your customers' phones. SMS boasts massive open rates, making it the perfect channel for flash restocks or limited-edition product runs.
• Understand Your Waitlist at a Glance: The app's clear subscriber dashboard shows you exactly who is waiting for what, giving you real-time, data-driven insights into where your demand is building.
• Build Trust with Custom Domain Sending: Protect your sender reputation and brand image. Your restock and price drop notifications are sent directly from your store’s own email address rather than a generic app domain, resulting in higher deliverability rates and better customer trust.

Best for: KBite is the perfect match for new merchants setting up a customer recovery workflow for the first time. It is a highly intuitive, zero-coding tool that lets you launch automated sequences in minutes without a steep learning curve. This makes it incredibly easy to instantly reach high-intent buyers via automated email and SMS text alerts.

3. Notify! Back in Stock | PreOrder

Pricing: Free plan available + paid plan

• Kickstart: $9.90/month
• Starter: $19.90/month
• Standard: $39.90/month

Notify Me! covers more ground than almost any other recovery tool by combining email, SMS, and push notifications into a single install. While standard apps only handle back-in-stock alerts, Notify! tracks the entire customer journey by seamlessly covering wishlists, pre-orders, and low-stock alerts to capture intent at every stage of the funnel.

Image source: Notify Me! on Shopify App Store

Like most recovery apps, it covers all the essential customer touchpoints right out of the box, including a customizable "Notify Me" button, an intuitive subscriber form, an instant confirmation message, and a friendly thank-you note.

Setting everything up is completely straightforward by simply filling out clear, dedicated text fields for your header and main content, then adjusting the styling button and form to match your brand.

Image source: Notify Me!

What really makes Notify! different is its built-in multi-step flow. Instead of giving up after the initial "First Back in stock" alert, the app lets you automatically send a Reminder Notification via email, SMS and push notification if the customer hasn't purchased yet. This gives you a second chance to capture their attention, combat busy inboxes, and recover lost revenue from high-intent buyers who simply forgot to check out the first time.

Image source: Notify Me!

Besides standard restock alerts, it packs a robust set of features to maximize your sales potential and streamline your operations:

• Advanced Configurations: Level up your logic by setting minimum inventory thresholds so alerts only trigger when stock fully recovers, sending notifications even when Shopify's "track quantity" is turned off, or overriding settings to send alerts while "Continue selling when out of stock" is active (from Rocket plan).
• Advanced Sales Boosters: Drive urgency and capture early revenue with built-in low-stock counters, B2B presales, and preorders.
• Frictionless Wishlist: Lower the barrier to buy with a rare, no-login wishlist that lets customers save items without creating an account, significantly boosting your conversion rates.
• AI-Powered Campaigns: Save time with the built-in "Notify me assist" AI tool, which tracks request freshness and distribution data to identify high-interest items and maximize restock ROI.
• Shopify POS Integration: Never miss a sale in the physical world. It bridges your online and offline retail by turning in-person inquiries into trackable demand data, letting you know exactly what to restock for your next in-store event.
• Flexible Checkout Options: Secure sales upfront and improve cash flow by accepting partial payments, a feature available starting right from their standard plan (from Standard plan).
• Seamless Tech Stack Connections: Keep your workflow running smoothly with native links to the marketing tools you already use, including Klaviyo, Omnisend, Mailchimp, PushOwl, PageFly.

Best for: Notify Me! is ideal for multi-channel Shopify merchants bridging online and offline retail with Shopify POS integration. It is perfect for store owners wanting to maximize conversions by sending automated follow-up reminder alerts to busy shoppers rather than relying on a basic, one-and-done notification. If you want to consolidate your app stack by managing email, SMS, push, B2B preorders, and wishlists under a single system, Notify Me! is the perfect fit.

4. Preorder, Back In Stock - STOQ

Pricing: Free plan + paid plan

• Lite: $10/month
• Pro: $29/month
• Unlimited: $69/month

Stoq is a dual-engine back-in-stock app for Shopify that combines hyper-targeted restock alerts with a flexible pre-order and deposit system. It optimizes conversions by localizing alerts to specific Shopify Markets and letting shoppers request exact item quantities upfront. Best of all, it seamlessly connects with your existing marketing stack like Klaviyo and keeps your subscriber data clean using built-in double opt-in verification. 

Source: STQD on Shopify App Store

Stoq gives you proactive control over your supply chain and customer data. Here is exactly what sets it apart from standard notification tools on the market:

• Forecast exact demand volume: Shoppers can specify the exact quantity they want right inside the alert form. This gives you clear, upfront data on true restock demand before you place your next inventory order.
• Rescue broken form submissions: When customers make a typo in their email or phone number, Stoq displays a custom error message on-screen to guide them to fix it immediately, instead of letting them walk away frustrated.
• Keep your subscriber data clean: A built-in double opt-in setting requires shoppers to confirm their registration via email. This filters out fake bots and ensures you only collect high-quality, high-intent lead data.

Source: STOQ

• Match your existing marketing stack: You can send alerts instantly using Stoq's native setup or route subscriber data directly through Klaviyo or Shopify Flow to unlock advanced customer segmentation.
• Avoid confusing your global customers: Fully integrated with Shopify Markets. If an item restocks in a US warehouse, Stoq tracks location data and only alerts US buyers, ensuring UK or EU shoppers aren't notified by mistake.

Stoq boosts merchant revenue by doubling as a highly flexible pre-order engine. Instead of losing sales on out-of-stock items, you can swap your buy button with a pre-order widget to capture immediate upfront payments, or lower the purchase barrier by offering partial payments and fixed deposits.

Best for: International brands using Shopify Markets who need hyper-localized restock alerts, fast-growing stores running limited or viral product drops that require automated follow-up reminders, and merchants scaling their pre-order strategy through flexible customer deposits and partial payments.

5. REZ Preorders, Back In Stock

Pricing: Complimentary at this time

REZ stands out as an incredibly cost-effective powerhouse because it is currently completely free. If your priority is maximizing your store's functionality at zero cost, REZ delivers back-in-stock, preorders and partial payments, which are almost always locked behind expensive upgrades in other apps. 

Image source: REZ on Shopify App Store

REZ also offers a free preorder feature with deposits and partial payments, which reduces the barrier to purchase for high-ticket or long-lead-time preorder items. Instead of demanding the full amount upfront, this feature allows you to collect flexible deposits or partial down-payments from customers to lock in their upcoming inventory.

When looking at what's missing, REZ offers fewer links to third-party apps compared to its paid competitors. For users, this means you may have to handle customer data transfers manually or miss out on syncing your subscriber lists directly with your primary email marketing platforms like Klaviyo or Omnisend.

Best for: REZ is ideal for budget-conscious or growing Shopify merchants looking to maximize their features at zero cost while managing high-value items, custom waitlists, or long production times. It is particularly perfect for businesses that need advanced capabilities like preorders and partial payments without paying a premium monthly subscription.

6. Amp Back in Stock | PreOrder

Pricing: Free plan + paid plan

• Lite Plan: $19/month
• Startup: $29/month
• Small Business: $49/month

Despite its simple setup, AMP is a powerhouse that has delivered hundreds of millions of alerts for over 25,000 brands, making it one of the most thoroughly tested and battle-proven options on the Shopify App Store. 

Image source: Amp on Shopify App Store

AMP makes multi-channel restock alerts simple and highly scalable, allowing you to send back-in-stock notifications seamlessly through email, SMS, and web push notifications. Setting up your alerts is completely straightforward, you just fill out the default content fields like any standard app to get your campaigns live in minutes.

Image source: Amp on Shopify App Store

While it scales effortlessly for high-volume catalogs, AMP's absolute greatest strength is ultimate control

• Build sequence: Add an extended sequence of up to 4 follow-up notifications combined with automated discount codes (Upgrade to Lite plan or higher).
• Precision Widget Controls: Define exactly when and where buttons appear, automatically hide them for specific tagged products, or turn them off for items where inventory is not tracked by Shopify.
• Smart Delivery & Batching: Delay alerts for a set period after restocking, establish a minimum stock threshold before triggers fire, choose peak hours for maximum engagement, and throttle delivery by controlling how many customers are notified at a time.
• Multi-Location Targeting: Select exactly which fulfillment or retail locations connect to your back-in-stock logic to keep localized inventory accurate.
• Webhooks & API: Scale your operations with API token access and HTTP callbacks to stream live notification events directly into custom systems or databases.

Best for: AMP is best for high-volume Shopify merchants needing total control over restock logic, delivery pacing, and multi-location inventory. Additionally, its robust API and webhook support make it the ideal fit for stores requiring advanced developer tools to connect with custom tech stacks. 

How to Choose the Right Shopify Back in Stock App for Your Store

Not every store has the same needs, so there’s no single “best” Shopify back-in-stock app. Instead, focus on the key factors that actually matter before you spend money on one.

1. Notification Channels

Think about where your customers actually are.

• Start with email if you're new to restock alerts or selling everyday products. It works for any business, supports rich content like images and pricing blocks, and opens the door to broader email marketing later. All apps in this list support email notifications.
• Add SMS when products sell out fast. Flash drops and limited releases need immediate action. SMS gets seen in minutes, not hours. Supported by: Kbite, Notify!, STOQ, Amp, and Appikon.
• Add WhatsApp if you're selling to Latin America, Southeast Asia, Middle East, or India. It's the primary communication channel in these regions, and works best when customers need to ask questions before buying. Only Notify! and Duck offer this channel.
• Use push notifications only if you already have a mobile app with strong adoption. Don't build an app just for restock alerts. It's not worth it. Notify! and Amp both support push.

Start with email. Add channels based on what your analytics show, where traffic comes from, and what devices customers use. Test one at a time and track cost per conversion, not just open rates.

If you want all four channels without testing one by one, Notify! is the only app in this list covering email, SMS, push, and WhatsApp - activate what works, pause what doesn't.

2. Automation Capabilities 

Most back-in-stock apps send one alert to everyone the moment a product restocks. That works for stable inventory, but some stores need more control.
XFlow uses a workflow builder for scenario-based alerts. Instead of a single global alert, you build logic around your specific inventory situation.

• Tag VIP customers based on purchase history: Automatically tag new subscribers as VIP if they have made more than 5 orders or spent more than a threshold amount.

Image source: Workflow template by XFlow

• Follow-Up Sequences: Send the initial alert. If a customer doesn't purchase within 48 hours, trigger a follow-up with a reminder or a limited-time discount to push them over the line.

Image source: Follow-up sequences created by using XFlow

Amp offers delivery policy controls for batch sending. Instead of notifying all subscribers at once when a product restocks, you can control how many customers get alerted and when based on inventory levels, time zones, and waitlist size.

Source image: Amp help docs

If you just need basic restock alerts, any app works. For limited drops or customer prioritization, XFlow and Amp are the only options in this list. XFlow offers deeper control with triggers and conditions. Amp keeps it simple with batch timing.

3. Customization and Branding

Your "Notify Me" button and restock emails should feel like part of your store, not a third-party app tacked on.

Most apps handle the basics well. You can customize the notification button - change colors, logo, adjust text, control placement. The same goes for the success message customers see after they subscribe. Nearly every app in this list supports this level of customization.

XFlow goes deeper with a drag-and-drop email builder. You're not locked into a rigid template-you can add sections, rearrange layouts, include product recommendations or customer reviews, and design emails that actually match your brand. XFlow also lets you send from your own domain instead of a generic app address, which helps with both trust and deliverability.

Image source: Email template by XFlow

4. Integrations

Using Klaviyo, Omnisend, or Mailchimp? Make sure your app connects to it. Notify!, STOQ, Amp, and Duck all support Klaviyo. For Shopify Flow, Amp has the deepest integration. Need restock data in an ERP or data warehouse? Amp is the only app with a Webhook and API.

For stores with physical locations, Notify! and STOQ are the only two apps here with Shopify POS support.

Image source: STOQ

5. Pricing

Most apps have a free plan for basic use. Here's a quick breakdown:

• Currently free: XFlow, REZ
• Most affordable paid: STOQ ($10/mo)
• Higher entry price: Notify! ($19.90/mo), Amp ($19/mo)
• Good free plans for small stores: Kbite, REZ, STOQ

If price is the top priority, start with XFlow or REZ. Each has its strengths:

XFlow - Better email design and automation. Run multiple campaigns, track demand, and recover lost sales from stockouts.

REZ - Combines Preorders and Back in Stock in one app. Email design is basic.
For growing brands, price isn't everything. Better design, automation, and segmentation can drive higher conversions - which often outweighs a lower monthly fee.

6. Extra Features Beyond Restock Alerts

Not every store needs the same tools. Some run simple restock campaigns. Others manage preorders, price drops, and inventory across multiple scenarios. Here's what each app offers:

Simple Add-Ons (Easy to Implement)

• Price drop alerts (Kbite): Notify customers when products go on sale, not just restock
• Wishlist + low stock urgency (Notify Me!): Let customers save products they want and signal scarcity to drive conversions

Advanced Features (Require Planning)

• Preorder & backorder management (STOQ, Notify!, REZ): Collect orders before inventory arrives
• Deposit & partial payment options (STOQ, REZ): Collect revenue upfront with flexible payment schedules

Which Features Actually Matter for Your Store?

• Wishlist features give you demand signals early; when customers save products before restock, you know what to order more of.
• Preorder and deposit features require more planning. They change your cash flow, fulfillment workflow, and customer communication. If you're collecting revenue before stock arrives, payment flexibility matters. Essent provides the most control: set exact deposit amounts, create multi-stage payment schedules, or collect percentage-based payments. STOQ, REZ, and Globo support deposits but offer fewer customization options-you're locked into preset structures.
• Avoid feature creep: Extra functionality means more to configure, more customer questions, and operational complexity. Choose features that solve real problems in your business.

7. SKU Volume and Scale

Running hundreds or thousands of SKUs? Not all apps handle high catalog volume equally well. Amp is built for scale. It has sent hundreds of millions of alerts across 25,000+ brands-more real-world proof than any other app here. When you're managing a large catalog, you need infrastructure that won't slow down during high-traffic restocks or choke when processing thousands of simultaneous alerts.

What to look for at scale:

• Performance under load - Can the app handle 10,000 waitlist subscribers for a single product? What happens when 50 products restock at once?
• Bulk management - You can't configure alerts product-by-product. You need rules at the collection level or store-wide settings with the ability to override for specific products.
• Reporting clarity - More SKUs mean more data. You need dashboards that quickly show which products have the most demand, which alerts convert, and where inventory gaps cost you sales.
• API reliability - High-volume stores often integrate with inventory management systems or ERPs. Mature infrastructure matters.
• If you're running a small catalog (under 100 SKUs), any app will work. For large stores with frequent restocks across multiple categories, proven scale matters.

8. Report

Knowing which products have the longest waitlists helps you reorder smarter. Appikon excels at this with demand reports that rank products by waitlist size. STOQ and Amp also offer solid dashboards for tracking subscriber interest.

XFlow goes further by showing which restock campaigns actually generated sales. You see order attribution - how much revenue each campaign drove, conversion rates, and exactly which products sold after alerts went out. XFlow also tracks variant-level subscription data (which sizes and colors have the most demand), so you know exactly what to restock before ordering.

Image Source: XFlow

Frequently Asked Questions about Choosing The Best Back-in-stock App

1. What basic features should I look for in a back-in-stock app?

A basic back-in-stock app should cover three core areas:

• Notification channels: Email is standard across all apps. More advanced tools also support SMS, WhatsApp, and push notifications, which are useful depending on your customer base and sales urgency.
• Customization options: The app should let you adjust key brand elements such as the “Notify Me” button, email design, logo, product image, and subject line. This ensures the experience feels native to your store.
• Demand reporting: Basic analytics that show waitlist size and product-level demand help you understand what customers actually want and improve restocking decisions.

2. What’s the difference between back-in-stock alerts and preorder features?

Back-in-stock alerts notify customers after a product becomes available again, while preorder features let customers purchase before inventory arrives. Back-in-stock captures existing demand, whereas preorders generate revenue in advance. Some apps support both, but they serve different stages of the buying journey.

3. Do I need a developer to set up a back-in-stock app?

No. Most Shopify back-in-stock apps are designed for no-code setup and can be installed in minutes. Basic features like “Notify Me” buttons and email alerts are typically plug-and-play. However, advanced capabilities such as APIs, webhooks, or custom workflows may require technical setup or developer support.

4. Which types of businesses need partial payment (deposit) features?

Partial payment or deposit features are most useful for businesses selling high-value, made-to-order, or inventory-constrained products. This includes stores that want to secure revenue before full fulfillment is possible or reduce purchase friction on expensive items.

Common use cases include:

• High-ticket products (e.g., furniture, electronics, luxury goods)
• Custom or made-to-order items
• Preorder-based product launches
• Limited production runs with long lead times

Final Thoughts

If you only manage a few stable products, manual tracking might seem doable. But as your catalog grows, manual work quickly becomes impossible.

A dedicated back-in-stock app shifts you from guesswork to automated precision. It saves hours of admin work, ensures no high-intent buyer slips through the cracks, and provides clear demand reports so you know exactly what to restock.

With that data in hand, the next step is selecting the software to execute your strategy. Choosing the right tool simply comes down to your store's scale:

• For small stores: Plug-and-play tools like REZ or Kbite handle basic email and SMS alerts with zero setup complexity. You can also leverage XFlow, which is currently free yet offers advanced product-level control right out of the gate.
• For scaling brands: One-size-fits-all rules aren't enough. High-volume stores need the precise, product-level logic of XFlow or the heavy-duty delivery infrastructure of Amp.

By matching the tool to your operational size, you turn unavoidable stockouts from a revenue leak into a hands-off, high-converting recovery engine.