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zBay revolutionizes online marketplaces by decentralizing eBay, empowering merchants and buyers. It enables seamless data and reputation import from eBay, secure escrow, XMTP chat, and transparent dispute resolution using the Uma optimistic oracle


Created At

ETHGlobal Waterloo

Winner of


🥇 Gnosis Chain — Best Use


🥇 Airstack — Best Use


8️⃣ FVM — Top 8


🏊‍♂️ UMA — Pool Prize


🔗 Sismo — Best Onchain App


🥈 The Graph — Best Use of Existing Subgraph


🥇 XMTP — Best Use


🏆 ETHGlobal Waterloo 2023 Finalist

Project Description

zBay - Democratizing Online Marketplaces

zBay is a project aimed at revolutionizing the online marketplace industry by decentralizing and democratizing the existing eBay platform. Our mission is to empower merchants and buyers by removing intermediaries and providing a secure, transparent, and efficient marketplace for everyone to participate in. Motivated by eBay's staggering $10 billion in fees earned in 2022, we believe it's time to reshape the landscape of online commerce. To achieve this, we have implemented three key components within the zBay platform:

  • Importing Data and Reputation: We recognize the value of established merchants on eBay and understand the importance of reputation in the online marketplace ecosystem. With our decentralized approach, we allow merchants to seamlessly import their existing data and reputation from eBay, ensuring a smooth transition for those who wish to leverage our decentralized marketplace. By preserving and transferring reputation, we aim to build trust among participants, enabling them to benefit from their established track records.
  • Escrow Mechanism: Trust is fundamental to any successful online marketplace. To enhance trust and security, we have implemented an innovative escrow mechanism within zBay. This mechanism acts as a safeguard, ensuring that funds are securely held until both buyers and sellers have fulfilled their obligations. By incorporating this layer of protection, we aim to mitigate fraudulent activities and instill confidence in the decentralized marketplace. To ensure smooth and secure communication between buyer and seller, we have implemented XMTP chat around the product.
  • Dispute Handling: Inevitably, disputes may arise during transactions. To address this challenge, we have integrated the Uma optimistic oracle framework into zBay’s infrastructure. This cutting-edge technology allows for efficient and fair dispute resolution by leveraging decentralized consensus and verifiable off-chain data. With Uma, we ensure that disputes are handled transparently and in a timely manner, promoting an equitable marketplace experience for all participants.

Our vision for zBay is to empower merchants and buyers by providing them with greater control, reduced costs, and improved transparency compared to traditional centralized marketplaces. By democratizing eBay, we aim to foster a thriving ecosystem where participants can interact in a secure and trustless manner.

How it's Made

The suite is deployed on Polygon Mumbai, Ethereum Goerli, and Gnosis Mainnet. Main contracts are verified.

  • Seller
  • Should first verify their reputation with any of the two methods:
    • By using Sismo Connect and submitting a proof of Gitcoin Passport score to be verified on
    • By using an eBay profile importer (via puppeteer) which uses zk-circuit to validate the reputation and verify proof on chain
  • Then sellers can create products manually or via import from eBay (via apify)
  • Product metadata is stored via on ipfs
  • After buyer purchases the product, seller dispatches the shipment and sends an attestation=`hash(secret + trackingNumber + buyerAddress) on chain to be verified via a the proof later by the buyer
  • Seller can communicate with the buyer about the product and delivery via XMTP


  • Buyers browse products using backend endpoint built on thegraph API
  • Buyers can purchase the product they like buy paying its price + insurance deposit based on the reputation calculated using airstack
  • Buyers can communicate with the sellers about the product via XMTP
  • To prove the receipt of the shipment buyer should provide a proof of `hash(secret + trackingNumber + account) to be verified on chain


  • Any party can also dispute the transaction via UMA


  • Sismo for Proof of Gitcoin Passport score
  • zk-snarks for reputation: circom circuit + backend proof generation + on-chain proof verification
  • zk-snarks for attestation: circom circuit + backend proof generation + on-chain proof verification


  • vite + react
  • rainbowkit + wagmi + viem
  • @chakra-ui for layout and UI


  • nest.js
  • Apify to parse ebay product info
  • puppetter to parse ebay profile
  • thegraph for smart contract db
  • airstack for reputation coefficient

Snap (not integrated, though implemented):

  • display reputation of the seller

Smart Contracts:

  • hardhat + solidity
  • unit-tests to simplify development
  • UMA for Optimistic Oracle and dispute resolution
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