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The Hiero JSON-RPC Relay is an open-source service that speaks the Ethereum JSON-RPC protocol on top of the Hedera network. EVM tools (Hardhat, Foundry, Ethers.js, Viem, MetaMask) speak JSON-RPC; Hedera consensus nodes speak gRPC. The relay translates between the two, plus pulls historical state from a mirror node. Repository: hiero-ledger/hiero-json-rpc-relay. License: Apache-2.0.

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Three ways to get an RPC endpoint

For most teams, “running the relay” means picking one of three options based on the use case.
OptionWhen it fitsCost
Hashio (free public relay, development use only)Development, hobby projects, low-volume readsFree, throttled
Third-party managed provider (Arkhia, Validation Cloud, Hgraph, QuickNode, thirdweb)Production traffic with SLAsPaid, varies by provider
Self-hostedProduction workloads where you control config, retention, and rate limitsInfra cost only
Hashio is the easiest path for “I just need a testnet endpoint right now.” It’s not intended for production traffic.

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Public endpoints

NetworkChain IDHashio endpoint
Mainnet295https://mainnet.hashio.io/api
Testnet296https://testnet.hashio.io/api
Previewnet297https://previewnet.hashio.io/api
Drop one of these into MetaMask, Hardhat, or Foundry as your RPC URL with the matching chain ID. You’re done. For production, replace Hashio with your own relay or a commercial provider.

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When to run your own

Self-hosting makes sense when you need any of:
  • Higher throughput than community endpoints throttle to
  • Custom rate-limiting rules per consumer
  • Tighter control over which mirror node the relay reads from
  • An RPC endpoint inside a private VPC, not on the public internet
  • Specific log retention, metrics, or audit requirements
If none of these apply, a managed provider is almost always less operational work.

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Next steps

Setup

Install and run the relay locally or in a container orchestrator.

Configuration

Environment variables, chain ID, mirror node URL, caching, rate limits.