Primer

Primer is a Chrome extension that makes crypto payments on Amazon feel completely seamless. Since Amazon doesn’t actually support digital assets, we built a smarter bridge that preserves the checkout experience users already know. The insight was realizing that gift cards could serve as an invisible settlement layer.

Here is how it works: our extension injects a “Checkout with Crypto” button directly into the Amazon order page, styled in Amazon’s own design system so the experience feels native. When clicked, users connect a wallet such as Coinbase Wallet, MetaMask, or Phantom. They send USDC or another supported asset to our merchant address, and the transaction is verified instantly using Coinbase’s CDP Data API. The moment the funds are confirmed, our backend automatically purchases and applies Amazon gift cards to the order.

The brilliance of the workaround is that the user never touches a gift card code or even knows this is happening. There is no copy-paste, no switching platforms, no interruption in the flow. The conversion from crypto to gift card value happens entirely in the background, so the shopper experiences a checkout flow that feels identical to paying with a credit card. Installation is incredibly simple as well! Add our Chrome extension with one click, and you instantly unlock Primer’s benefits.

As a result, our design makes crypto spending on Amazon not only possible but frictionless. The global e-commerce market exceeds $1.7 trillion, and there are more than 1.7 billion unbanked individuals worldwide who struggle with access to traditional financial rails. We believe that mainstream adoption of crypto payments requires abstracting away all the visible edges of crypto UX. Primer does this by embedding Web3 rails into a Web2-native flow, giving users the benefits of digital assets without forcing them to change their habits.

Our Chrome extension is built using TypeScript, React, SQLite and Chrome Extension APIs, with Webpack 5 handling the build process.

The core integration involves the Coinbase Wallet SDK, which handles wallet connections, transaction signing, and USDC balance management. We've also integrated MetaMask and Phantom wallets using wagmi connectors, and using the curl commands from CDP Data API for blockchain interactions like tracking USDC transactions and verifying confirmations when the merchant address gets an amount that is just a little above the product value.

The most sophisticated integration is with Coinbase CDP (Customer Data Platform), which creates an automatic bridge between crypto payments and gift card fulfillment. When a user completes a crypto payment, the CDP tracks the transaction and automatically triggers the gift card application process on Amazon, eliminating manual intervention.

Our backend uses Node.js and Express.js with SQLite for gift code inventory management and webhook processing.

The automation system is built with custom DOM manipulation code rather than external libraries, using a sophisticated selector system that adapts to Amazon's dynamic page structure. We use multiple communication channels including postMessage, localStorage, and custom listener events to maintain reliable data flow between the extension's isolated contexts.

Since crypto confirmations can be slow/unpredictable, we built a polling solution with our webhook-based backend listener that tracks wallet with payment confirmation and Amazon gift card triggers, and purchases the item then.

Our project started with an analysis of all the other ideas that were possible ranging from banking/ACH solution with Coinbase offramp, creation of virtual card, other non-custodial approach, etc. Through this process, we identified the recurring shortcomings in existing “crypto-to-Web2” payment projects: reliance on custodial intermediaries, latency in settlement, and brittle checkout integrations that break with minor UI changes. By dissecting these models and stress-testing alternatives, we designed a leaner flow where the transaction verification, wallet integration, and fulfillment logic are coupled tightly together, eliminating the common points of failure and making the crypto-to-Amazon checkout bridge technically robust.