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Relayers

Relayers keep the light-client bridge in sync with Bitcoin by submitting Bitcoin block headers to the bridge's Relay contract on the destination chain. The Relay verifies each header against Bitcoin's consensus rules, so the inclusion proofs that wraps, unwraps, and slashing rely on are always checkable.

What a relayer does​

  • Retrieves data (block headers) from Bitcoin (the source chain).
  • Submits them to the Relay contract, which validates and stores valid headers and rejects invalid ones.

Permissionless & collateral-free​

This is a key difference from validator-based bridges:

  • Anyone can run a relayer — the relayer script is lightweight and runs on a small server.
  • No collateral required. Relayers only provide input; the contract independently rejects anything invalid, so there's nothing to slash.
  • One honest relayer is enough for safety — as long as at least one honest relayer submits the latest headers within a reasonable time, the bridge stays correct and live.
  • Submitting invalid data is simply unprofitable: it earns no reward while still costing the relayer the destination-chain gas.

Incentives​

Relayers are paid from bridge fees that querying apps/users pay on the destination chain. The model (per the TeleSwap light-client protocol):

BridgeReward = K × SubmissionGas × GasPrice
BridgeFee    = K × SubmissionGas × GasPrice × EpochBlocks / PrevEpochQueries
  • The first relayer to submit a header that becomes finalized on the Relay earns the reward — covering its gas plus a margin.
  • The per-query fee falls as usage rises (more queries in the previous epoch → lower fee).

Relayers are the foundation the other roles build on — Teleporters and Lockers submit proofs that are only verifiable because relayers supplied the headers.