How do I mock the Ethereum JSON-RPC API locally?

Install stunt, add a one-service block to stunt.yaml (adapter: embedded:eth-jsonrpc-style), and run stunt up. You get a local, stateful stand-in for Ethereum JSON-RPC 1.0 — 1 routes over rest — with no remote account, no network, and no bills.

Is the Ethereum JSON-RPC mock data synthetic?

Yes — entirely. The adapter returns generated data only; stunt's adapter lint rejects real-looking secrets and PII at build time. It simulates the shape and behavior of Ethereum JSON-RPC (routes, status codes, pagination, webhooks), never real records.

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eth-jsonrpc-style

simulates Ethereum JSON-RPC 1.0

restadapter v0.1.01 routes

verification

SDKverified with go-ethereum v1.17.5· surface 1 · not implemented 5 · differs 4

use it

# add to stunt.yaml
services:
  eth-jsonrpc:
    adapter: embedded:eth-jsonrpc-style

# then
$ stunt up

The embedded: source extracts this adapter from the binary — no git clone, fully offline.

how to mock the Ethereum JSON-RPC API locally

Install stunt, paste the service block above into stunt.yaml, run stunt up — then point your client at localhost instead of Ethereum JSON-RPC. It works offline, keeps state across requests and restarts, and every response is synthetic: the route shapes, status codes, pagination, and webhook delivery follow the real Ethereum JSON-RPC 1.0 surface — the data is fake, the behavior is real.

backing stores

transactionsreceiptslogsblocks

api surface (1)

generated from the adapter manifest — exactly what boots, nothing more

1 routes

POST/

SDK-verified behaviors (5)

✓ethclient.ChainID + BlockNumber
✓BalanceAt decodes seeded hex-quantity wei
✓CodeAt returns empty (no EVM execution)
✓HeaderByNumber returns the genesis header
✓PendingNonceAt for an untouched account

Not implemented (5)

No EVM execution — eth_getCode always 0x, contracts never run
No eth_getStorageAt, eth_getTransactionByBlock*, or uncle methods
No debug/trace namespaces (debug_traceTransaction, trace_transaction)
No eth_maxPriorityFeePerGas or eth_blobBaseFee methods
No WebSocket subscriptions (eth_subscribe); HTTP POST / only

Differs from the real API (4)

eth_estimateGas fixed at 0x5208 (21000); eth_gasPrice fixed at 1 Gwei
Tx hashes derive from a pseudo-keccak, not real keccak256
Mining delay fixed at 3s; blockNumber advances one block per sent tx
eth_sendRawTransaction accepts simulator-only {simulate_fail: true} for a revert

full scorecard →

want more of the Ethereum JSON-RPC surface? adapters are YAML + Starlark — the authoring guide covers adding routes, fixtures, and state machines. Open an issue for anything big first, or just file a PR — merged routes ship in the next release.