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Relayer

An off-chain actor or service that observes one blockchain and submits messages or proofs to another system.

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Definition

An off-chain actor or service that observes one blockchain and submits messages or proofs to another system.

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Why it matters

Interoperability allows assets, messages, and applications to operate across otherwise separate networks.

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How it works

Relayers continuously listen to events on a source blockchain via its API or RPC nodes. Once an event is detected, they package the transaction proof and broadcast it to the destination blockchain, where a smart contract verifies the proof against the source chain’s known state.

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Real-world example

In the Cosmos ecosystem, anyone can run a relayer process to help pass packets between networks like Cosmos Hub and Osmosis.

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Advantages

  • Facilitates permissionless message transport
  • Decentralized operation models
  • Essential for protocol connectivity

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Limitations

  • Relayers may require economic incentives
  • Risk of censorship if not diverse
  • Maintenance intensive for operators

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Common misconceptions

  • Relayers are the ones moving the funds. Relayers only move proof of funds; the smart contracts on both chains handle the actual asset management.
  • Relayers can forge transaction data. Relayers cannot change data because the target chain always verifies the cryptographic proof against the source chain’s state.
Canonical knowledge ID: glossary:relayer