Case Study: Transforming Shopify Collection Filters for True Inventory Accuracy

Overview

A Shopify merchant using a premium theme approached me with a recurring pain point: the default "Availability" filters and product stock messaging on collection pages did not reflect the real-time inventory situation. Their goal was to offer a more transparent shopping experience and give customers better tools to find what's actually in stock.

The Challenge

• Shopify's native availability filter treats products with "Continue selling when out of stock" enabled as in-stock—even when inventory is zero.
• Product pages showed accurate inventory messages, but collection pages didn't.
• The merchant wanted consistent messaging across product and collection pages and a truly accurate "In Stock"/"Out of Stock" filter.
• The solution needed to be fast, scalable, and integrate seamlessly with their heavily customized Shopify theme.

Solution Design

To overcome Shopify's limitations, I proposed a hybrid approach combining theme customization, Shopify's Storefront API, and a lightweight JavaScript app.

Key Features Delivered:

• Accurate stock messaging on collection pages using the same logic as product pages.
• Custom inventory filter that ignores the "Continue selling" flag and uses true inventory counts.
• Real-time UI updates on filter selection, reflecting correct product counts.
• Pagination and filter persistence using cookies for consistent UX across browsing sessions.

Technical Highlights

• Storefront API Integration: Fetched complete product lists to determine actual inventory levels.
• Custom Filtering Logic: Overrode Shopify's default logic to reflect only real stock.
• Dynamic Messaging: Matched collection page stock messages to those on the product pages (e.g., "Currently out of stock", "We have 3 in stock").
• Filter Persistence: Used cookies to retain filter state across pagination and filter selections.
• Search Template Extension: Later extended this functionality to the search results page for consistency across the storefront.
• Edge Case Handling: Resolved issues with Vendor Collection pages, variant inventory mismatches, and dynamic product counts.

Tech Stack

Results

• Fully accurate "In Stock" and "Out of Stock" filters based on live inventory.
• Consistent and clear stock messages across collection and product pages.
• Improved customer trust and reduced friction in product discovery.
• Seamless integration with the merchant's theme and future-proof architecture.
• Follow-on work from the client to replicate the same filters on their second store.

Why It Matters to eCommerce Managers

As an eCommerce Manager, you're constantly looking for ways to:

• Increase trust and reduce returns from stock-related surprises
• Streamline the product discovery process
• Improve site usability without sacrificing theme integrity

This project proves that it's possible to overcome Shopify's default limitations and build a more transparent, conversion-optimized storefront—without waiting for a feature update from Shopify.