Stop multi-size carts before they become size returns
CartProof detects bracketing on Shopify in real time. When a shopper adds 2+ sizes of the same item, it triggers a fast fit check with one recommended size, before checkout.
The moment a shopper adds two sizes to cart
Most sizing tools react after the return has already shipped. CartProof reacts at the moment uncertainty shows up in the cart.
Multi-size carts inflate return exposure
One uncertain shopper can turn into multiple outbound shipments, multiple reverse-logistics events, and a refund instead of an exchange.
Generic fit tools create friction for everyone
Most sizing apps interrupt every shopper, even the ones who already know exactly what they want.
Merchants lack a bracketing KPI
You can see returns after the fact, but most teams can't see bracketing rate by product or size run in a way they can act on.
Detect, guide, reduce waste
CartProof is built around one narrow job: catch bracketing in the cart and help the shopper commit to one size.
Detect the add
Shopper adds 2+ sizes of the same item to cart.
Guide the decision
CartProof triggers a quick fit check and recommends one size with confidence language.
Reduce waste
Fewer multi-size checkouts, fewer size and fit returns, cleaner margin.
What early access gets your brand
CartProof ships as a lightweight pilot, not a long implementation cycle, so you can see results on real traffic fast.
A pilot built for your highest-return SKUs
We start with 1-2 sizing-sensitive products, like denim, bras, or swim, where bracketing is already costing you the most.
A theme snippet and script, not a full app install
V1 runs as a lightweight pilot so you can test before committing to a heavier tool.
A clear read on savings per 1,000 orders
We track bracketing rate, conversion, and size/fit returns so you leave the pilot with a number, not a guess.
A say in what the first reporting looks like
Early-access brands help shape bracketing-rate-by-SKU reporting before it's built for everyone else.
For Shopify apparel brands with sizing-sensitive SKUs
CartProof is built for teams that already feel the cost of shoppers ordering multiple sizes just to try them on at home.
Denim, bras, and swim brands
Categories where fit is unpredictable across cuts and sizes, so bracketing and size returns run highest.
Ecommerce managers tracking return rate
You already know your size/fit return percentage and want a lever that acts before checkout, not after.
Founders protecting margin on high-return SKUs
You want fewer reverse-logistics events without adding friction for shoppers who already know their size.
Questions, answered
Does this replace our size chart or fit widget?
No. CartProof does not act like a generic size chart. It only triggers when a shopper adds 2 or more sizes of the same product to cart, then shows one recommended size with an easy-swap message.
Is this only for denim, bra, and swim brands?
Those categories see the most bracketing because fit varies the most, but any apparel brand with meaningful size/fit returns can pilot CartProof.
What will it cost?
CartProof is expected to be a subscription, priced against your measured return savings. Exact pricing is not set. Early pilot brands help validate that anchor and may get preferred access.
When can we actually start using this?
Pilot spots open in stages, starting with brands on high-return SKUs. Joining the waitlist puts you in line for the first round.
What happens with our email after we sign up?
We use it only to reach out about pilot access and share early results. No spam, no lists sold, unsubscribe any time.
Does it slow down checkout for shoppers who already know their size?
No. CartProof only triggers on multi-size carts, so shoppers who add one size and check out see no change at all.
If multi-size carts are driving your returns, join now
We're looking for Shopify apparel brands ready to test a focused bracketing pilot on their highest-return products.