How Does a Crypto Bridge Work? Lock, Relay, or Mint
How can a token bridge operate? It doesn't usually move the same coin from one blockchain to another: it logs a deposit on the source chain, checks that event, and releases, mints, or draws on liquidity an equivalent asset on the destination chain. The path, bridge design, and finality rule shape what arrives, how quickly it arrives, and who receives each fee.
The main mechanisms behind a bridge system
Many bridges connect distinct networks by moving assets or messages between them, because blockchains cannot directly communicate with one another. Ethereum’s bridge overview puts the key designs into three working models:
- Lock and mint: the starting token is locked in a source-chain contract, while a version is minted on the destination chain.
- Burn and mint: the token is destroyed on the source chain and created again on the destination chain.
- Liquidity transfer: a pool or trading firm pays the recipient on the destination chain, then later settles between chains.
That second asset is often a wrapped token: a token on one network that tracks an asset held elsewhere. It is not the original coin magically crossing a boundary; it is a representation, a newly issued representation, or destination liquidity paid against a verified source event.
Where the fees goes
A bridge transaction can contain several different costs:
- Source gas: paid to the source blockchain for giving the token approval and calling the bridge contract.
- Bridge or routing fee: retained partly by the protocol, relayer, liquidity provider, or route operator.
- Price impact: charged indirectly when the destination pool has low liquidity or the route requires a swap.
- Destination execution cost: paid by the bridge, deducted from the output, or left for the user when claiming funds.
This is why the amount credited can be smaller even when the listed “bridge fee” looks small. A service such as gnosis bridge can fit the experience into one screen, but the actual outcome still rests on which contract receives the deposit, which mechanism supplies the destination asset, and whether the quote includes gas and execution costs.
Why bridges finish at different speeds
A canonical bridge may wait for a message or transaction to become final ahead of releasing funds. A liquidity bridge can send funds first and settle later. Across shows the second with relayers, while Stargate demonstrates shared cross-chain liquidity.
I had this wrong the first time: I treated “sent” as being “arrived.” I never again judge a bridge by the wallet animation; I look at the source transaction, destination asset type, recipient amount, and all fees in the quote.