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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 middleware 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>