Multi-Chain NFT Marketplace with Auctions

Project overview

We built an NFT marketplace for a startup serving digital artists and collectible brands. Creators set up collections, upload artwork, choose fixed-price or auction sales and set royalties; collectors browse, bid and buy with their own wallets, and resales pay the original creator automatically.

The engagement covered product discovery, marketplace and auction contracts in Solidity, IPFS storage, the Next.js storefront, event indexing and an admin console for curation and moderation. It is part of our blockchain development services and draws on the marketplace patterns we use across multi-vendor platforms.

The client and the challenge

Creators on the client's launch list did not want to pay gas before anything sold, and several wanted to sell on more than one EVM-compatible chain. Collectors needed assurance that artwork and metadata would not vanish if a server went down, and the startup needed a way to handle stolen or infringing uploads without controlling users' assets.

Auctions added their own problems: last-second bids, refunds for outbid users, and keeping listings, bids and ownership in the storefront consistent with what the chain actually recorded. Search also had to stay fast as collections grew, because querying the chain directly for every page view would have been slow and costly.

Solution architecture & delivery

Artwork and metadata are pinned to IPFS and referenced by content identifier, so the token points to a hash of the file rather than a URL we control. Creators can lazy mint: they sign a voucher describing the token, price and royalty off-chain, and the NFT is only minted on-chain when a buyer purchases it, with the buyer's transaction covering gas. The contract verifies the creator's signature and that the voucher has not already been redeemed.

The marketplace contract handles fixed-price sales, offers and English auctions. Bids are held in escrow by the contract; when someone is outbid, their funds become claimable rather than being pushed back automatically, which avoids failed refunds blocking the auction. A bid in the final minutes extends the end time to stop sniping. Royalties follow the common on-chain royalty standard and are paid out in the same transaction as each sale.

Each supported chain has its own deployment of the contracts, and an indexer listens for mint, list, bid, sale and transfer events on every chain and writes them into a single searchable catalogue. The Next.js storefront reads that catalogue for browsing and filtering, but always checks ownership and listing state on-chain before a user signs. Gas estimates, network switching prompts and transaction tracking keep users informed at every step.

Moderation works at the marketplace layer: admins can hide a collection from the storefront, freeze its listings in our contract and mark it for review, but cannot move tokens held in user wallets. Releases and contract deployments went through staged testnets as described in our CI/CD and testing pipeline.

Key features we built

• Collection creation with artwork and metadata pinned to IPFS
• Lazy minting from signed vouchers so creators pay no upfront gas
• Fixed-price listings, offers and timed English auctions
• Escrowed bids with claimable refunds and anti-sniping extensions
• Automatic creator royalties paid on every resale
• Multi-chain deployments with one unified, searchable catalogue
• Gas estimates, network switching and clear transaction status
• Admin console for curation, reports and listing freezes

How we delivered it

1. Discovery. Interviews with launch creators and collectors shaped sale formats, royalty rules, chain choices and moderation policy.
2. Contract design. Voucher, marketplace and auction contracts were specified and tested with unit and fuzz tests, including adversarial bidding scenarios.
3. Build. Two-week sprints delivered the storefront, IPFS upload pipeline, multi-chain indexer and admin console in parallel.
4. Audit and launch. An independent contract audit was completed and findings fixed before launching on one chain, followed by further chains once indexing was proven.
5. Support. Ongoing support covers indexer monitoring, new chain deployments, featured drops and moderation tooling. Creator onboarding guides and a help centre were written alongside the launch.

Technology choices

• Next.js — server-rendered collection and item pages that search engines can index, combined with client-side wallet interactions.
• Solidity — the language of EVM chains, letting one audited contract set be deployed to each supported network.
• IPFS — content-addressed storage so artwork and metadata are referenced by hash and remain retrievable independently of our servers.

Outcomes

• Creators list work without paying gas until a sale happens
• Artwork and metadata are verifiable by content hash rather than tied to a single server
• Creators receive royalties automatically on secondary sales
• Collectors browse one catalogue across chains instead of separate marketplaces
• Auctions handle outbid refunds and late bids without manual intervention
• The team can moderate reported collections without taking custody of user assets

FAQ