Field notes

What we learned building the thing, written down.

Notes on Shopify carts, checkout systems and storefront performance, from the team that ships four apps on the App Store. Mechanisms and primary sources. New notes land as we hit something worth writing down.

01 · Latest

1 note · Atom feed

Cart & Checkout · 4 August 2026 · 12 min read

Adding a fee to the Shopify cart, without a product

Shopify has no primitive for “charge a bit extra.” Here is what merchants build instead, why the usual workaround quietly breaks four other things, and what the Cart Transform API actually changed.

Onik G., Engineering Read the note

02 · Writing next

On the bench

The cart-fee note is the first of a cluster. These are the ones already on the bench. No dates, because we publish when the thing is actually true.

Cart Transform expand, operation by operationApp engineering
Credit-card surcharges: where they're legal and what the card networks requireCart & Checkout
Shipping protection without giving away a revenue shareCart & Checkout
Theme app extensions vs script tags: what actually changedStorefront

Normalize · Commerce software studio

We write these because we ship the code.

Four apps on the Shopify App Store, plus cart, checkout and storefront engineering for merchants worldwide. If a note here describes a problem you have, we can probably fix it.

Start a project See the apps