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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. 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

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.
Testing relay configuration locally? Solo ships with a JSON-RPC relay as part of its full-stack Kubernetes deployment. Use it to test custom chain IDs, rate limits, and mirror node URL wiring against a local network before deploying to production. See Using Solo with EVM tools for connection details.

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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.