battles / Checkout
FastSpring vs Rebuy
FastSpring ($750/mo/mo, vibe code 3/10) vs Rebuy ($285/mo/mo, vibe code 5/10). Rebuy is the easier one to rebuild yourself — here is what you lose either way.
Checkout
$750/mo/mo
- MVP
- 2 weeks
- Full replacement
- Never (Requires global tax entities, banking rails, legal indemnification)
Checkout
$285/mo/mo
- MVP
- 1-2 weeks
- Full replacement
- 6-12 months
easier to rebuild
get the build prompt →price gap / year
$5,580/mo
running both / year
$12,420/mo
our call
Start with Rebuy — highest vibe code, weakest moat.
FastSpring
FastSpring is not just checkout software; it assumes legal and financial liability as the Merchant of Record. Rebuilding the checkout UI in React is trivial, but self-hosting global VAT/GST compliance, localized payment acquirers, and fraud liability requires massive legal infrastructure.
you can rebuild
- Embeddable checkout UI modal and hosted payment pages
- Basic subscription management and recurring billing webhooks
- License key generation and digital file fulfillment triggers
- Customer portal for invoice downloads and subscription cancellations
- Multi-currency storefront price conversion displays
what you lose
- Merchant of Record legal status and cross-border indirect tax liability assumption
- Automated VAT/GST calculation, collection, and filing across 200+ global jurisdictions
- Global payment gateway routing, localized payment methods (iDEAL, Pix, Alipay), and acquirer optimization
- Merchant-level chargeback and fraud liability protection
- Payer of record status handling international currency conversion payouts
real moats
- Global legal and tax registration network with local tax authority filings
- Underwritten acquiring bank relationships and payment processing infrastructure
- Financial liability indemnification for chargebacks, VAT audits, and sanctions checks
open source escape hatches
- Kill Bill Apache-2.0
- Lago AGPL-3.0
- Hyperswitch Apache-2.0
Rebuy
You can easily build a custom slide-out cart and a basic Shopify Checkout UI Extension using modern AI coding agents in a weekend. However, duplicating Rebuy's cross-app integrations, ML recommendation graphs, and cross-channel merchandising flows requires significant long-term maintenance.
you can rebuild
- Slide-out Smart Cart drawer with progress bars and dynamic item injection
- Basic merchandise cross-sell and upsell widgets on product and cart pages
- Shopify Checkout UI extension upsell blocks
- Post-purchase upsell modals using standard Shopify APIs
- Rule-based product recommendation flows (if product X is in cart, show Y)
what you lose
- Built-in ML product recommendation engine trained on millions of store orders
- Native deep integrations with subscription platforms like Recharge and Stay AI
- Rebuy Monetize revenue share network on thank-you pages
- Smart Search and smart collections engine
- A/B testing infrastructure for checkout and cart upsells
real moats
- Dataset of cross-store co-occurrence data across billions of e-commerce checkout events.
- Pre-built app-to-app integrations with Recharge, Klaviyo, Attentive, Route, and Okendo.
- Rebuy Monetize publisher network that pays merchants revenue-share on third-party offers.
open source escape hatches
Questions people ask
Which is easier to rebuild with AI, FastSpring or Rebuy?
Rebuy. It scores 5/10 on vibe code with a moat of 6/10, so an AI-assisted MVP takes about 1-2 weeks and a full replacement about 6-12 months.
Which one costs less, FastSpring or Rebuy?
Rebuy at $285/mo/mo for a typical mid-market store. The gap between the two is about $5,580/mo a year.
What do I lose if I replace FastSpring?
Merchant of Record legal status and cross-border indirect tax liability assumption Automated VAT/GST calculation, collection, and filing across 200+ global jurisdictions Global payment gateway routing, localized payment methods (iDEAL, Pix, Alipay), and acquirer optimization
What do I lose if I replace Rebuy?
Built-in ML product recommendation engine trained on millions of store orders Native deep integrations with subscription platforms like Recharge and Stay AI Rebuy Monetize revenue share network on thank-you pages
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