NFT Aggregator Development: Order Indexing, Sweeps and Routing

An NFT aggregator shows listings from many marketplaces in one place and lets a buyer purchase across those marketplaces in one transaction. This guide explains the two hard parts: an up-to-date index of other marketplaces' orders and a safe router contract. It also covers features, revenue, risks and cost.

How NFT aggregators changed NFT trading

Gem and Genie were two early, large NFT aggregators. In 2021 and 2022, both let traders sweep the cheapest items in a collection from several marketplaces in one transaction, which saved time and gas. OpenSea bought Gem in 2022, and Uniswap bought Genie the same year.

OpenSea and other large marketplaces then added aggregation as a built-in feature, so a new aggregator needs a reason to exist beyond "all listings in one place". Typical reasons are a chain or niche with no good aggregator, tools for one type of trader, or aggregation inside another product such as a wallet or game.

Blur and the NFT marketplace aggregator model

Blur launched in late 2022 as a marketplace for professional traders with aggregation built in. The Blur NFT marketplace lets traders sweep listings from several marketplaces, advertises zero marketplace fees and pays BLUR token rewards for listing and bidding. The Blur Foundation documentation lists three parts of the ecosystem: the marketplace, its aggregation features and Blend, a protocol for loans backed by NFTs.

Blur's token rewards pulled a large share of Ethereum NFT volume in 2023. Much of that volume came from traders farming rewards, and it fell when Blur changed the rules of its reward periods, which it calls seasons.

Core features

• Unified feed: shows every active listing for a collection, with price, fees and expiry in one format.
• Price comparison: shows the total cost per item, including marketplace fees, creator royalties and gas.
• Cart and sweep: buys many selected items, or the cheapest N items, across marketplaces in one transaction.
• Search and filters: filters by trait, rarity, price, marketplace and listing age.
• Cross-listing: lists one item on several marketplaces at once, with the seller signing an order in each venue's format.
• Collection bids: shows the best offer across venues and lets an owner of an NFT in that collection accept it.
• Portfolio: shows holdings, estimated values, profit and loss, and activity.
• Payments: accepts ETH, stablecoins or other tokens and swaps them in the same transaction, and a card on-ramp serves buyers without crypto.
• Royalty display: shows each venue's royalty policy, and a buyer can choose to pay the full royalty where the venue makes it optional.

Architecture

The router contract

The router receives a list of purchase instructions, one per order, each naming a marketplace contract. For each instruction, the router calls that venue's fill function with the payment and sends the NFT to the buyer. The design has four main parts:

• All-or-nothing or partial fills: another buyer may purchase one item of a 20-item sweep just before the sweep transaction is confirmed. All-or-nothing routing then reverts the whole sweep, while partial-fill routing skips that item and refunds its funds, which most traders prefer.
• No standing approvals: buyers should not give the router broad token approvals, so the router takes exact payments, Permit2-style signatures or the chain's native currency.
• No custody: the router holds user NFTs or funds only inside one transaction, and any leftover balance goes back to the user in the same transaction.
• Venue adapters: each marketplace integration sits in its own module, so a new venue does not change the core logic.

A router calls many outside contracts, so attackers target it. A full smart contract audit and tight upgrade controls are required before launch.

Cross-listing

To list on several venues, the seller signs an order for each venue's protocol. Many EVM marketplaces use OpenSea's Seaport protocol, and Seaport 1.6 is deployed at the same contract address on Ethereum, Base, Polygon, Arbitrum and many other chains, so one token approval for Seaport can serve several venues. Each venue still sets its own fee recipients, so the aggregator must build each order with that venue's fee terms.

A sale on one venue moves the item to the buyer's wallet, and because the seller no longer owns it, the other listings fail on-chain. The interface should hide those listings at once, so buyers do not send transactions that fail.

Details traders notice

Professional traders switch tools quickly when these details are missing:

• All-in prices: the list sorts by price with marketplace fee, royalty and estimated gas included, not by the listing price.
• Freshness: each listing shows when it was last checked, and items disappear the moment they sell anywhere.
• Gas warnings: the app estimates gas before signing and warns when a sweep may hit the block gas limit.
• Private submission: large sweeps go through private relays, so bots cannot see them in the public mempool before they land.
• Bulk actions and keyboard shortcuts: a trader can list fifty items in one action.
• Source labels: each order shows its marketplace and royalty policy, so the buyer knows who gets paid.

How to build an NFT aggregator

1. Choose the chains and the niche. On Ethereum and its Layer 2 networks, most volume runs through Seaport-based venues and Blur, while Solana uses different venues and standards, as the Solana NFT marketplace guide explains.
2. Connect the order sources: marketplace APIs where they exist and on-chain events elsewhere. Get API terms in writing, because a venue can rate-limit or block an aggregator.
3. Build the normalized order book with continuous validation.
4. Build the router with venue adapters, partial fills and refunds, and test it against a fork of mainnet state.
5. Build the front end: collection pages, trait filters, cart, sweep, bids and portfolio.
6. Add token swaps for payment and, if needed, card checkout.
7. Audit the router, launch with a few venues and add venues over time.

Revenue models

• Aggregator fee on purchases, though competition pushed this fee to zero at many aggregators. Blur's marketplace, which also aggregates, charges no marketplace fee.
• Referral fees that some venues pay for routed volume.
• Paid tools such as analytics, alerts, faster data and bidding bots.
• Your own marketplace fees, if you also run a venue and route some volume to it.
• Featured collections and ads, labeled as paid placements.
• A native token, although reward tokens tend to attract wash trading and volume that leaves when rewards end.

Risks to plan for

• Source dependence: a major marketplace can block your API access and leave a gap in the feed, which on-chain fallbacks reduce.
• Provider churn: several NFT data and order-routing providers have shut down or changed prices since 2023, so wrap each integration behind your own interface so you can switch.
• Stale data: a buyer who pays gas for a failed purchase of a sold item often leaves, so measure data freshness and show it.
• Scams: many sources bring many fake collections, so keep a verified-collection list, flag lookalike contracts and never let listing metadata insert links or scripts into the page.
• Router exploits: one router bug can expose every user who gave the router a token approval, so keep approvals minimal, put upgrades behind a timelock and run a bug bounty from launch.
• Low volume: NFT trading volume is far below its 2021–2022 peak, so build revenue plans on the real volume in your niche.

Cost and timeline

These ranges are estimates based on the scope in each row, not quotes.

The NFT marketplace development guide covers a single marketplace with its own listings, and the cross-chain marketplace guide covers the messaging and bridge layer for trading across chains.

Frequently asked questions