Rye API Alternatives: 7 Checkout APIs for AI Agents (2026)

Short answer: The closest alternative to the Rye checkout API is Zinc: both let your app or AI agent buy products from retailers that never integrated with you. Rye is strongest on long-tail Shopify merchants. Zinc is built for big-box retailers (Amazon, Walmart, Target, and 20+ others) and adds tracking, returns, and pay-per-order over MPP or x402. If you only need merchants that opted into agent checkout, ACP or Google UCP may be enough.

Disclosure: this is Zinc's blog, and Zinc is on this list. We have tried to describe every option, including Rye, from its own documentation, so you can pick on fit rather than on who wrote the article.

• What Rye does
• Why teams look for a Rye alternative
• The 7 best Rye alternatives
• Comparison table
• How to choose
• FAQ

What Rye does

Rye sells two APIs for buying products from other stores inside your app:

• Universal Checkout API. Send a product URL and Rye returns real pricing, tax, and shipping, then completes checkout. Rye lists "15,000+ merchants," with Shopify as its most reliable surface. Amazon orders are placed through Rye's own Amazon account. Payments are tokenized through Stripe or Prava, and order status comes back by webhook. Rye's docs list it at $149/month after a free first month.
• Sync API. A GraphQL API with full cart support, limited to Shopify stores and Amazon. Amazon orders go through your own Amazon Business account, and pricing is based on GMV with a deposit.

Rye also markets integrations for ChatGPT and OpenClaw, and describes its Universal Checkout as "agentic checkout" for AI agents. Source: Rye's API comparison.

Why teams look for a Rye alternative

The reasons we hear most often:

1. Big-box coverage. Your users buy at Amazon, Walmart, Target, and Best Buy more than at independent Shopify stores.
2. Post-purchase depth. You need tracking numbers pulled from the retailer, split shipments, and a way to return items in code.
3. Payment model. You want per-order pricing, customers paying with their own cards, or an agent paying from its own wallet, rather than a monthly fee or a GMV deposit.
4. Protocol-first. You only need to buy from merchants that support agent checkout protocols, so a protocol is simpler than a checkout API.
5. Vendor risk. Checkout is critical infrastructure, and some teams want a second provider behind the same abstraction.

The 7 best Rye alternatives

1. Zinc: purchasing API for Amazon, Walmart, Target, and 20+ retailers

Zinc is a purchasing API that has been placing orders at retailers since 2014. Your app sends a product, a shipping address, and a max_price, and Zinc checks out as a shopper, then returns the order ID and tracking.

• Coverage: Amazon, Walmart, Target, Best Buy, and 20+ retailers. No merchant opt-in needed.
• After checkout: tracking numbers attached to every order automatically (tracking guide), webhooks, and a returns API.
• Payments: prepaid balance, Stripe Connect (your customer's card is charged per order, and you keep a margin), or per-order agent payments over MPP and x402.
• Agents: REST API, an MCP server, and the Universal Checkout agent skill (npx skills add zincio/skills --skill universal-checkout).
• Best for: gifting, rewards, procurement, and AI shopping agents where users expect the big retailers.

2. OpenAI ACP (Agentic Commerce Protocol)

ACP is the open protocol from OpenAI and Stripe behind Instant Checkout in ChatGPT. Merchants implement four checkout endpoints; agents call them with a Stripe Shared Payment Token.

• Coverage: only merchants that implemented ACP. Amazon, Walmart, and Target have not.
• Best for: merchants who want to sell to agents, and agents that only buy from ACP merchants.

3. Google UCP (Universal Commerce Protocol)

Google's open standard for agent checkout, with Shopify tooling for building commerce agents on top of it. Same model as ACP: the merchant exposes checkout, the agent calls it. Often paired with AP2 for payment authorization.

• Coverage: merchants that adopted UCP.
• Best for: being buyable inside Google's AI shopping surfaces, and agents that buy from UCP merchants.

4. Shopify's agent tooling

If the products your agent buys live on Shopify stores, Shopify's own agent tooling (built on UCP) gives you catalog and checkout without a third party.

• Coverage: Shopify merchants.
• Best for: apps whose catalog is mostly independent Shopify brands. This is the closest overlap with Rye's strongest surface.

5. CartAI

CartAI offers a white-label embeddable cart that supports ACP, UCP, and browser agents, aimed at publishers and AI surfaces that want to turn product mentions into purchases without sending readers away.

• Best for: content sites and AI apps that want an embedded buy flow rather than a raw API.

6. firmly

firmly works on the merchant side: it helps retailers become agent-ready so AI surfaces can check out with them, and it has powered checkout inside Perplexity.

• Best for: retailers who want to be bought by agents. It is a merchant-enablement tool, not a way for your app to buy from any store.

7. Build it yourself with browser agents

You can run your own checkout agent on browser infrastructure such as Browserbase or Kernel (Kernel publishes a case study with Rye). You own every retailer flow, account, CAPTCHA, and failure.

• Best for: teams with a narrow set of stores and engineers to maintain checkout scripts. Most teams find the maintenance cost higher than expected; see web scraping vs ecommerce APIs.

Comparison table

How to choose

• Your users buy everyday products at the big retailers: Zinc.
• Your catalog is mostly independent Shopify brands: Rye or Shopify's agent tooling.
• You only buy from merchants that support agent protocols: ACP or UCP directly.
• You run a content site or AI surface and want an embedded cart: CartAI.
• You are a retailer and want agents to buy from you: firmly, or implement ACP and UCP.
• You need full control and have a small set of stores: browser agents, with eyes open about maintenance.

A practical pattern for critical checkout: put your purchasing provider behind one internal place_order function. Switching or adding a second provider is then a change in one file, not a rewrite.

FAQ

What is the best alternative to Rye's checkout API?

For buying at Amazon, Walmart, Target, and other big retailers, Zinc: one API call places the order, and tracking and returns come back through the same API. For independent Shopify stores, Shopify's agent tooling covers much of the same ground.

Zinc API vs Rye API: what is the difference?

Both let software buy from stores that did not integrate with you. Rye's Universal Checkout emphasizes breadth across Shopify merchants with a product-URL flow and a monthly price. Zinc emphasizes big-box retailers, tracking extracted from the retailer, a returns API, and payment options including Stripe Connect and per-order agent payments over MPP and x402.

Does Rye work with Amazon?

Yes. Per Rye's docs, Universal Checkout places Amazon orders through Rye's own Amazon account, and the Sync API uses your own Amazon Business account.

Can ChatGPT buy products without Rye or Zinc?

Only from merchants that implemented ACP, through Instant Checkout. To buy at retailers that have not, ChatGPT needs a connected tool backed by a purchasing API.

How hard is it to switch from Rye to Zinc?

The core flow is the same: product in, order and tracking out. The work is mapping your order and webhook handling to the new payloads. Start in test mode and run both providers side by side before you switch traffic.

Related reading

• Agentic Checkout API: Let an AI Agent Buy Anywhere
• Universal Checkout API: Accept Payments or Buy Anywhere?
• Best Ecommerce Purchasing APIs for Developers
• What Is ACP?