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# Relay

## Overview

A **Relay** sits between a client and the **Tempo (Execution) RPC**. It acts as a
sidecar to the chain, providing offchain services that are impractical onchain
because of storage growth, cost, or operational requirements.

```mermaid
flowchart LR
  client[Client] --> relay
  subgraph relay[Relay RPC]
    direction TB
    multisig[Multisig]
    feePayer[Sponsorship]
    feeToken[Best Fee Tokens]
    simulate[Balance Diffs]
    funding["🚧 Funding"]
    accessKeyState["🚧 Access Key State"]
    multisig ~~~ simulate ~~~ accessKeyState
    feePayer ~~~ feeToken ~~~ funding
  end
  relay --> rpc["Tempo (Execution) RPC"]
```

The node behind the execution RPC executes transactions and enforces authorization.
A Relay prepares transactions and coordinates offchain state; it cannot bypass
chain rules. Clients rely on it for service availability and persistence.

## Plugins

Compose plugins to sponsor transactions, resolve fee tokens, simulate
balance changes, and coordinate multisig approvals. The transaction plugins share
the same object-based hook contract as custom plugins. Requests enter plugins in array
order, and responses return in reverse order.

Funding and access-key state plugins are planned.

<Cards>
  <Card icon="lucide:wallet" title="Fee Payer" description="Sponsor transaction fees with a local account or an external relay." to="/tempo/relay/plugins/fee-payer" />

  <Card icon="lucide:coins" title="Fee Token" description="Choose a funded fee token using the sender's preference and balances." to="/tempo/relay/plugins/fee-token" />

  <Card icon="lucide:scan" title="Simulate" description="Preview token balance changes and estimate fees before sending a transaction." to="/tempo/relay/plugins/simulate" />

  <Card icon="lucide:users" title="Multisig" description="Coordinate owner approvals and share pending multisig transactions." to="/tempo/relay/plugins/multisig" />
</Cards>

## See More

<Cards>
  <Card icon="lucide:workflow" title="Run a Relay" description="Host a Fetch endpoint with plugins for transaction preparation and coordination." to="/tempo/guides/relay/run" />

  <Card icon="lucide:network" title="Connect to a Relay" description="Connect your client to a remote relay or run plugins in your application." to="/tempo/guides/relay/connect" />
</Cards>