FeeLayer vs. legacy surcharge apps
Most Shopify surcharge apps were built before Cart Transform Functions existed. They rely on JavaScript injection or Checkout UI Extensions alone — both of which get bypassed by Shop Pay, Apple Pay, and Google Pay. Here's how FeeLayer is different.
Everything the leaders offer — at 20% of the price
Compared against the top surcharge apps on the Shopify App Store. Feature checks are based on publicly documented behavior and pricing as of April 2026.
Cart Transform Functions
Checkout Validation Functions (2nd enforcement layer)
Bypass-proof on Shop Pay, Apple Pay, Google Pay
US state compliance auto-waive
Card-brand caps enforced (Visa 3% / MC 4%)
POS + online parity
Theme App Extension (storefront disclosure)
Abandoned-cart safe (no draft orders)
Built in the USA
Pricing model
Monthly price (entry plan)
Source: Shopify App Store listings, vendor websites, and user-review analysis, April 2026. Features reflect default behavior on each app's entry-level plan; higher-tier plans may add capabilities that are only listed on paid tiers. Pricing shown is the lowest public plan, excluding free trials.
Most fee apps get bypassed at checkout.
Apps that rely on JavaScript injection or Checkout UI Extensions alone get stripped by Shop Pay, Apple Pay, and Google Pay. FeeLayer runs inside Shopify's infrastructure as two WebAssembly functions, so fees are enforced server-side.
JS injection + UI extensions
What most Shopify surcharge apps are running today.
- Express checkout (Shop Pay, Apple Pay, Google Pay) skips the UI extension
- Customers can strip the line-item fee from cart
- Cart Transform collisions when bundles are installed
- Mobile browser inconsistency (Android / iOS Safari)
Cart Transform + Validation Functions
Shopify's newest architecture — adopted here, not retrofitted.
- Server-side recalc on every cart mutation
- Checkout Validation rejects orders with tampered totals
- Express-checkout safe — Functions run before payment auth
- Theme App Extension for storefront disclosure
What to evaluate
Whichever surcharge app you're considering, run these questions against each option:
- Does it survive express checkout? Shop Pay, Apple Pay, and Google Pay skip most legacy fee injection paths. The app needs server-side enforcement — Cart Transform Functions — to apply the fee consistently.
- Is there a second enforcement layer? Checkout Validation Functions reject any order where totals have been tampered with. Without this, a motivated customer can strip the fee before paying.
- Does it handle state compliance? Surcharging is prohibited in Connecticut, Massachusetts, and Maine. Card-brand rules cap fees at 3% (Visa) and 4% (Mastercard), and debit surcharging is prohibited under the Durbin Amendment.
- Is it POS + online? If you run a physical store, make sure the same rules apply at the register and online — inconsistent fees confuse customers and staff.
- Pricing model. Flat-rate, volume-capped, or tiered? Tiered apps punish growth. Flat-rate keeps your costs predictable at any volume.
Try FeeLayer on your store
Install FeeLayer from the Shopify App Store and compare it against your current setup.