Technically, an NFT marketplace on Harmony is straightforward: the chain is EVM-compatible, so standard ERC-721 (HRC-721) and ERC-1155 contracts deploy as on Ethereum. The harder question is whether you should. Harmony's ecosystem shrank sharply after its Horizon bridge was hacked in 2022, and a marketplace needs users and liquidity that are now scarce there.
What Harmony is
Harmony is a proof-of-stake layer-1 that launched its mainnet in 2019 with a sharded design. Its consensus, Fast Byzantine Fault Tolerance (FBFT), aimed for fast finality, and its Effective Proof-of-Stake (EPoS) scheme was designed to spread stake across validators. Shard 0 acts as the beacon chain and is where nearly all smart-contract activity, including NFTs, takes place. The network has since reduced its number of active shards. Gas is paid in ONE, and addresses can be shown in Harmony's one1… format or the familiar 0x… format. The Harmony documentation covers current network details.
The Horizon bridge hack and its aftermath
In June 2022, attackers drained roughly $100 million from Harmony's Horizon bridge to Ethereum by compromising enough of the keys on its multisig, which reportedly required only two of five signatures. US authorities later attributed the attack to North Korea's Lazarus Group. Bridged assets on Harmony, such as bridged stablecoins, lost their backing and traded far below their face value. Recovery proposals were contested, and developer and user activity declined steeply.
For anyone building on any chain, the lesson is concrete: a bridge secured by a small multisig is a single point of failure for every asset that depends on it. Marketplaces that accepted bridged tokens as payment were directly exposed.
If you still build on Harmony
There are legitimate reasons: an existing community or game that already lives there, or a project for which the remaining ecosystem is enough. In that case, the build looks like this.
- Confirm infrastructure. Check that reliable RPC endpoints, a working block explorer with source verification, and an indexer or NFT API covering Harmony are available. Several services that once supported Harmony have dropped it.
- Deploy standard contracts. ERC-721 or ERC-1155 with EIP-2981 royalties, written and tested with Foundry or Hardhat pointed at Harmony's RPC.
- Use an audited exchange contract for signed listings and offers rather than custom matching code.
- Accept native ONE for payment and avoid assets whose backing depends on the old bridge.
- Run your own indexer if no hosted provider covers your needs; Harmony's RPC is Ethereum-compatible, so standard EVM indexing tools work.
- Plan an exit. Store metadata on IPFS or Arweave and keep a holder snapshot process so the collection can migrate if the network's outlook worsens.
Comparison with alternatives
| Chain | EVM-compatible | NFT ecosystem today | Notable risk |
|---|---|---|---|
| Harmony | Yes | Small and quiet | Ecosystem decline; limited infrastructure |
| Polygon PoS | Yes | Established, brand-friendly | Sidechain security model |
| BNB Smart Chain | Yes | Large retail base, thinner NFT culture | Validator centralization, scams |
| Ethereum L2s (Base, Arbitrum) | Yes | Growing, strong tooling | Sequencer centralization, fragmentation |
Because all of these are EVM-compatible, the same contracts and most of the same front end can move between them. That makes the chain decision lower-stakes than it looks, as long as you avoid chain-specific dependencies. See Polygon, BSC and Ethereum layer 2 guides for those paths.
Migrating an existing Harmony collection
If you run a collection on Harmony and want to move, you have two main options. You can snapshot current holders and airdrop an equivalent collection on the new chain, then declare the new contract canonical. Or you can let holders burn or lock tokens on Harmony and claim on the new chain, which proves intent but leaves inactive holders behind. Either way, communicate the canonical contract clearly and ask marketplaces to update listings. The mechanics overlap with cross-chain NFT marketplace design and multi-chain NFT support.
What the Harmony story teaches marketplace builders
- Pick chains by ecosystem durability, not only by fees and throughput.
- Treat every bridge as a trust assumption; prefer canonical rollup bridges or well-audited messaging with strong validator sets.
- Keep contracts standard and data portable so a chain move is possible.
- Do not price listings in bridged assets you cannot verify.
Frequently asked questions
Is Harmony still running?
The network continues to produce blocks, but activity, developer support and NFT trading are far below their 2021 levels. Check current explorer data and infrastructure support before committing.
What is HRC-721?
Harmony's name for the ERC-721 standard. Because Harmony is EVM-compatible, ERC-721 contracts work on it unchanged.
Can a Harmony NFT marketplace be moved to another chain?
Yes, largely. The contracts and front end are standard EVM code; the work is redeploying, migrating holders and rebuilding liquidity.