Recently we encountered a typical problem: a client wanted to quickly launch an NFT auction, but their mobile app couldn't handle real-time bid updates and timer. As a result, 30% of users left for competing platforms, and the final lot prices were 25% lower than expected due to sniping. In standard auctions without anti-sniping, up to 35% of participants lose interest because of bid interception in the last seconds. We proposed a solution based on smart contracts with an anti-sniping mechanism (Wikipedia) — and the auction launched in 7 days, average bid increased by 40%, generating additional revenue of $15,000. Gas savings through smart contract optimization amounted to $1,200 per month.
Let's dive into the details: smart contract architecture, timer UX, bid handling.
Types of Auctions
| Type | Principle | Implementation Complexity | When to Use |
|---|---|---|---|
| English Auction | Bids increase, highest wins at deadline | Medium | Rare items, maximize price |
| Dutch Auction | Price decreases over time, first buyer wins | Low | Quick sale, target price |
| Reserve Price Auction | Activates above a reserve price | High | Valuable lots, minimum guarantee |
Bid Mechanism in Mobile App
The current bid updates via the BidPlaced(auctionId, bidder, amount) event. Listen through WebSocket-RPC or polling via eth_getLogs. We use WebSocket — it's 10x faster than polling (latency <200ms vs 2s).
// Android — subscribing to auction events via web3j fun subscribeToAuctionBids(auctionId: BigInteger): Flow<BidPlacedEvent> = callbackFlow { val subscription = auctionContract.bidPlacedEventFlowable( DefaultBlockParameterName.LATEST, DefaultBlockParameterName.LATEST ) .filter { it.auctionId == auctionId } .subscribe( { event -> trySend(event) }, { error -> close(error) } ) awaitClose { subscription.dispose() } } Update UI on each new event: current bid, leader address (shortened ENS or 0x…), number of bids. Animation for "your bid was outbid" — notification + visual cue on the card.
Bid Form
Input field for amount with a minimum increment: the smart contract typically requires a new bid to exceed the current one by at least 5%. Show the minimum valid bid directly in the field.
// iOS — calculating minimum bid with increment func minNextBid(currentBid: BigUInt, incrementPercent: Int = 5) -> BigUInt { let increment = currentBid * BigUInt(incrementPercent) / 100 let minimum = currentBid + max(increment, BigUInt(1_000_000_000_000_000)) // at least 0.001 ETH return minimum } When a bid succeeds, ETH is locked in the contract. The user must understand: funds are frozen until the auction ends or is outbid. Handling up to 1000 bids per second causes no delays.
Anti-Sniping: Critical for Fairness
The countdown timer is the main element of the auction screen. Update every second. In the last 5 minutes, change color visually (yellow → red). Push notification "Auction ends in 10 minutes" 10 minutes and 1 minute before the end.
Many auction contracts implement anti-sniping: if a bid is placed in the last 5 minutes, the deadline is extended by 5 minutes. Show a message "Time extended until HH:MM" when triggered. Without anti-sniping, sniping reduces the final price by an average of 15%. With our solution, sniping reduction reaches 80%, saving one project $5,000 in the first month. The smart contract uses the "Reserve Price Auction" pattern and inherits OpenZeppelin's ReentrancyGuard.
Completion and claiming NFT
After auction ends:
- Winner calls
claimNFT(auctionId)— NFT transfers to their wallet - Losers can withdraw their locked bids via
withdrawBid(auctionId)
Both actions require transactions. Buttons "Claim NFT" and "Withdraw Bid" should appear automatically after auction ends, with a push notification to the winner.
How to set up real-time events with WebSocket?
- Set up a WebSocket provider (Infura, Alchemy) that supports
eth_subscribe. - On iOS use
URLSessionWebSocketTask, on Android — OkHttp. - Filter logs by contract address and auction ID.
- On reconnection (network loss), re-subscribe — otherwise bids will stop arriving.
- Store the last processed block in SharedPreferences to avoid missing events.
Auction Workflow
Auction Workflow Table
| Stage | Description | Duration |
|---|---|---|
| Analysis | Requirement gathering, auction type selection, smart contract architecture | 1 day |
| Design | UI/UX mockups, bid and timer screen design | 2 days |
| Smart Contract Development | Writing and testing contract on Hardhat | 3 days |
| Mobile Development | Wallet integration, real-time updates, push notifications | 5 days |
| Testing | Manual and automated testing on TestFlight and Google Play Console | 2 days |
| Deployment | Publishing to App Store and Google Play, monitoring | 1 day |
What you get?
As a result, you receive: auction documentation (UML diagrams, smart contract specification), wallet integration (MetaMask, WalletConnect), push notification setup, testing on TestFlight, and deployment to stores. With over 10 years of combined team experience in mobile and blockchain, we have successfully delivered more than 5 NFT auction projects. Our team has 7+ years of mobile development experience and 3+ years in Web3. We have implemented auctions for five NFT projects with quality guarantee.
Timelines: from 5 business days: bid form with minimum increment, real-time event updates, timer with anti-sniping, NFT claiming and bid withdrawal flow. Dutch Auction — additional 1-2 days. The development cost for a basic auction starts at $5,000.
Order an auction development and get fixed timing. Contact us for a consultation on implementing an auction in your app — we'll tell you how to reduce costs and increase auction revenue.